# [LONG] Theoretical estimates for film-equivalent digital s..

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Last response: in Digital Camera

Anonymous

March 6, 2005 11:50:36 AM

Archived from groups: rec.photo.digital (More info?)

This or similar topics appear quite often, but most treatments avoid

starting "from first principles". In particular, the issues of

photon Poisson noise are often mixed up with electron Poisson noise,

thus erring close to an order of magnitude. Additionally, most people

assume RGB sensors; I expect that non-RGB can give "better" color

noise parameters than (high photon loss) RGB. [While I can easily

detect such errors in calculations of others, I'm in no way a

specialist, my estimates may be flawed as well... Comments welcome.]

Initial versions of this document were discussed with Roger N Clark;

thanks for a lot of comments which lead to major rework of

calculations; however, in order of magnitude the conclusions are the

same as in the beginning of the exchange... [I do not claim his

endorsement of what I write here - though I will be honored if he does

;-]

I start with conclusions, follow with assumptions (and references

supporting them), then conclude by calculations, and consideration of

possible lenses.

CONCLUSIONS:

~~~~~~~~~~~

Theoretical minimal size of a color sensor of sensitivity 1600ISO,

(which is equivalent to Velvia 50 36x24mm in resolution and noise)

is 13mm x 8.7mm. Similar B&W sensor can be 12x8mm. Likewise,

theoretical maximum sensitivity of 3/4'' 8MP color sensor is

1227 ISO.

[All intermediate numbers are given with quite high precision; of

course, due to approximations in assumptions, very few significant

digits are trustworthy.]

These numbers assume QE=1, and non-RGB sensor (to trade non-critical

chrominance noise vs. critical luminance noise). For example, in a

2x2 matrix one can have 2 cells with "white" (visible-transparent)

filter, 1 cell with yellow (passes R+G) filter, another with cyan

(passes G+B) filter.

ASSUMPTIONS:

~~~~~~~~~~~

a) Photopic curve can be well approximated by Gaussian curve

V(lambda) = 1.019 * exp( -285.4*(lambda-0.559)^2 )

see

http://home.tiscali.se/pausch/comp/radfaq.html

b) Solar irradiation spectrum on the sea level can be well approximated

by const/lambda in the visible spectrum (at least for the purpose

of integration of photopic curve). See

http://www.jgsee.kmutt.ac.th/exell/Solar/Intensity.html

http://www.clas.ufl.edu/users/emartin/GLY3074S03/images...

In the second one lower horizontal axis is obviously in nm, and the

upper one complete junk. Sigh...)

c) Sensitivity of the sensor is noise-bound. Thus sensitivity of

a cell of a sensor should be measured via certain noise level

at image of 18% gray at normal exposure for this sensitivity.

d) The values of noise given by Velvia 50 film and Canon 1D Mark II

at 800ISO setting at image of 18% gray are "acceptable". These

two are comparable, see

http://clarkvision.com/imagedetail/digital.signal.to.no...

Averaging 15 and 28 correspondingly, one gets 21.5 as the "acceptable"

value of S/N in the image of 18% gray.

e) Noise of the sensor is limited by the electron noise (Poisson noise

due to discrete values of charge); other sources of noise are

negligeable (with exposition well below 40sec). See

http://www.astrosurf.com/buil/d70v10d/eval.htm

f) The AE software in digital cameras is normalizing the signal so

that the image of 100% reflective gray saturates the sensor.

[from private communication of Roger Clark; used in "d"]

g) Normal exposure for 100ISO film exposes 18% gray at 0.08 lux-sec.

See

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00...

h) The color "equivalent resolution" numbers in

http://clarkvision.com/imagedetail/film.vs.digital.1.ht...

may be decrease by 25% to take into account recent (as of

2005) improvements in demosaicing algorithms. E.g., see

http://www.dpreview.com/reviews/konicaminoltaa200/page1...

Taking largest numbers (Velvia 50 again, and Tech Pan), this gives

16MP B&W sensor, and 12MP color sensor.

i) Eye is much less sensitive to the chrominance noise than to

luminance noise. Thus it makes sense to trade chrominance

noise if this improves luminance noise (up to some limits).

In particular, sensors with higher-transparency filter mask give

much lower luminance noise; the increased chrominance noise (due

to "large" elements in the to-RGB-translation matrix) does not

"spoil" the picture too much.

j) To estimate Poisson noise is very simple: to get S/N ratio K, one

needs to receive K^2 particles (electrons, or, assuming QE=1,

photons).

METAASSUMPTION

~~~~~~~~~~~~~~

In any decent photographic system the most important component

of performance/price ratio is the lenses. Since the price of the

lens scales as 4th or 5th power of its linear size, decreasing

the size of the sensor (while keeping S/N ratio) may lead to

very significant improvements of performance/price.

Details in the last section...

[This ignores completely the issue of the price of accumulated

"legacy" lenses, so is not fully applicable to professionals.]

Since sensor is purely electronic, so (more or less) subject to

Moore law, the theoretical numbers (which are currently an order

of magnitude off) have a chance to be actually relevant in not

so distant time. ;-)

PHOTON FLOW OF NORMAL EXPOSURE

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

First, we need to recalculate 0.08 lux-sec exposure into the the

photon flow.

Assume const/lambda energy spectral density (assumption b),

integration of photonic curve gives const*0.192344740294

filtered flow. With constant spectral density at

1 photon/(sec*mkm*m^2), const = h * c, so the eye-corrected energy

flow is 3.82082403851941e-20 W/m^2 = 2.60962281830876e-17 lux.

Thus 0.08 lux-sec corresponds to (constant) spectral density

3065.57711860622 photon/(mkm*mkm^2). This is the total photon flow

of the image of 18% gray normally exposed for 100ISO film.

B&W SENSOR

~~~~~~~~~~

One can imagine (among others) 3 different theoretical types of B&W

sensor: one giving "physiologically correct" response of the

photopic curve, one accepting all photons in the "extended visible"

range of the spectrum 380 to 780nm, and an intermediate one, one

accepting all photons in the "normal visible" range of the spectrum

400 to 700nm. See

http://en.wikipedia.org/wiki/Visible_light

To cover the first case, one needs to multiply the value obtained in

the previous section by the integral of the photopic curve,

0.106910937 mkm; for the other, one needs to multiply by the width

of the window, 0.4 mkm, and 0.3 mkm. Resulting values are

327.7437, 1226.23, and 919.673 photon/mkm^2 as the flow of 18% gray

normally exposed for 100ISO film.

However, since photopic curve should not produce any particularly

spectacular artistic effect, it makes sense to have the sensor

of maximal possible sensitivity, and achieve the photopic response

(if needed) by application of a suitable on-the-lens filter. So we

ignore the first value, and use the other two. For example, the

smaller value gives photon Poisson noise S/N ratio of 21.5 with a

square cell of 0.70896 mkm. The larger value of the window,

0.4 mkm, results in a square cell of 0.613977 mkm. These are

smallest possible sizes of the cell which can provide the required

S/N ratio at exposure suitable for 100ISO film.

To have 1600ISO sensor, these numbers should be quartupled; 16MP

3:2 ratio sensor based on the 0.4mkm spectral window results in

12x8mm sensor.

OPTIMIZING THE COLOR MASK

~~~~~~~~~~~~~~~~~~~~~~~~~

For color sensor, theoretical estimates are complicated by the

following issue: different collections of spectral curves for the

filter mask can result in identical sensor signal after suitable

post-processing. (This ignores noise, and de-mosaicing artefacts.)

Indeed, taking a linear combination of the R,G,B cells is equivalent

to substituting the transparency curves for mask filters by the

corresponding linear combination. (This assumes the linear

combination curve fits between 0 and 1.)

As we saw in B&W SENSOR section, a more transparent filter results

in higher S/N at the cell; if the filter is close to transparent,

cell's signal is close to luminance, thus higher transparency

results in improvement of luminance noise.

To estimate color reproduction, take spectral sensitivity curves

of the different types of sensors cells. Ideally, 3 linear

combinations of these curves should match the spectral sensitivity

curves of cones in human eyes. Assuming 3 different types of sensor

cells, this shows that spectral curves of cells should be linear

combinations of spectral sensitivity curves of cones. In

principle, any 3 independent linear combinations can be used for

sensors curves; recalculation to RGB requires just application of

a suitable matrix. However, large matrix coefficients will result

in higher chrominance noise. (Recall that we assume that [due to

high transparency] the luminance is quite close to signals

of the sensors, thus matrix coefficents corresponding to luminance

can't be large; thus all that large matrix coefficients can do is

to give contribution to CHROMINANCE noise.)

Without knowing exactly how eye reacts to chrominance and luminance

noise it is impossible to optimize the sensor structure; however,

one particular sensor structure is "logical" enough to be close to

optimal: take 2 filters in a 2x2 filter matrix to be as transparent

as possible while remaining a linear combination of cone curves.

This particular spectral curve is natural to call the W=R+G+B curve.

Take two other filters to be as far as possible from W (and

from each other) while keeping high transparency; in particular,

keep the most powerful (in terms of photon count) G channel, and

remove one of R and B channels; this may result, for example, in

the following filter matrix

W Y W Y W Y W Y

C W C W C W C W

W Y W Y W Y W Y

C W C W C W C W

here C=G+B, Y=R+G. Since the post-processing matrix R=W-C, B=W-G,

G=C+Y-W does not have large matrix coefficients, the increase in

chrominance noise is not significant.

Above, W means the combination of the cone sensitivity curves with

maximal integral among (physically possible) combinations with

"maximal transparency" being 1. While we cannot conclude that this

results in the optimal mask, recall the following elementary fact:

to estimate the maximal *value* f(x) one can make quite large errors

in the *argument* x, and still get good approximation for f(xMAX).

Thus choosing the matrix above gives a pessimistic estimate, AND one

should expect that it is not very far of the correct one.

TRANSPARENCY OF THE COLOR MASK

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Actually, what is R, G, B in colorimetry are in turn linear

combinations of responses of cones. Use cones sensitivity curves

from

http://www.rwc.uc.edu/koehler/biophys/6d.html

Now use RR, GG, and BB to denote *these* curves, not "usual" R, G, B

of colorimetry. Since I could not find these data in table form,

the values below are not maximal possible, but just first

opportunities which come to mind.

Using 0.9RR+0.35GG, one gets a quite flat curve; one may assume that

in range 0.42--0.65nm the sensitivity is above 0.9. with one at

700nm going down to 0.6, and 400nm going down to 0.8. So the

filter "compatible" with cone sensitivity curves can easily achive

0.9 transparency in the range 400--700nm, which would give photon

count 827.705822 photon/mkm^2 in the W (R+G+B) type cell. Taking

GG and 0.9RR+0.35BB curves as other types of sensors, one gets

average transparency about 0.8 and 0.85. Taking average

transparency of the filter over a 2x2 WCWY matrix cell 0.85, one

gets photon count averaged over different kinds of color-sensitive

cells as 781.722165 photon/mkm^2.

As above, we assume that this average photon count is the count

giving contribution into luminance noise.

FINAL ESTIMATES

~~~~~~~~~~~~~~~

With above average photon count at a cell, to get S/N ratio 21.5

one needs a square cell of 0.768975 mkm. Recall that this is the

the smallest possible cell which can provide the required S/N ratio

at exposure suitable for 100ISO film.

Quadrupling to get sensitivity 1600ISO, and taking 12MP equivalent

of 36x24mm Velvia 50, one gets the 13 x 8.7 mm sensor.

HOW GOOD CAN 36x34mm SENSOR GO?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In other direction, 36x24 mm color sensor at sensitivity 1600ISO can

(theoretically) be equivalent (or better) than 10 x 6.6 cm Velvia 50

film; that is 1/2 frame of 4x5 in film. In yet other words, take

36x24mm sensor with resolution and noise better than 4x5 Velvia 50

film; it has theoretical maximum of sensibility at 800ISO.

Likewise, to achieve resolution and noise of 8x10in Velvia 50 film,

the maximal sensibility of 36x24mm sensor is 200ISO.

THE QUESTION OF LENSES

~~~~~~~~~~~~~~~~~~~~~~

Of course, preceeding section completely ignores the issue of

lenses; on the other hand, a cheap prosumer zoom lens with

28--200mm equivalent paired with a digital sensor easily gives

resolution of 3.3mkm per single line (with usable image diameter

about 11mm, see

http://www.dpreview.com/reviews/konicaminoltaa200/page1...

); so we know it is practically possible to create a lens which

saturates the theoretical resolution of 1600ISO sensor (but probably

not 800ISO and 200ISO sensor!). It is natural to expect that a

non-zoom lens could saturate resolution of 800ISO sensor.

This gives theoretical resolution limit of a "practical" lens +

800ISO digital 36x24mm sensor: it is equivalent to best 4x5in 50ISO

film (with non-zoom lens). With zoom lense, one can achieve quality

of 2.5x4in 50ISO film; sensor is at 1600ISO, lense is 28-200mm zoom.

Some more estimates of how practical is "practical": the zoom

mentioned above is bundled with $600 street price camera which

weights about 580g. Assume the lens takes 1/2 of the price, and

1/4 of the weight. Rescaling from 11mm diagonal image size to the

36x24mm image size will increase price to $70K--$280K (assuming that

price is proportional to 4th-5th power of the size [these numbers

were applicable 20 years ago, I do not know what holds today]), and

will increase the weight to 9kg.

On the other hand, the 4:3 aspect ratio sensor of the same area as

the mentioned above 13 x 8.6 mm sensor (1600ISO sensor equivalent

in quality to Velvia 50 at 36x24mm) is 12.2 x 9.17mm, diagonal is

15.26mm. It is 0.9'' sensor (in the current - silly - notation).

Rescaling the mentioned above lens to this size gives lens price

$1100--$1500, and weight about 750g; both quite "reasonable".

Recall that this 28--200 equivalent zoom lens will saturates resolution

of an equivalent of Velvia 50 36x24mm film.

This or similar topics appear quite often, but most treatments avoid

starting "from first principles". In particular, the issues of

photon Poisson noise are often mixed up with electron Poisson noise,

thus erring close to an order of magnitude. Additionally, most people

assume RGB sensors; I expect that non-RGB can give "better" color

noise parameters than (high photon loss) RGB. [While I can easily

detect such errors in calculations of others, I'm in no way a

specialist, my estimates may be flawed as well... Comments welcome.]

Initial versions of this document were discussed with Roger N Clark;

thanks for a lot of comments which lead to major rework of

calculations; however, in order of magnitude the conclusions are the

same as in the beginning of the exchange... [I do not claim his

endorsement of what I write here - though I will be honored if he does

;-]

I start with conclusions, follow with assumptions (and references

supporting them), then conclude by calculations, and consideration of

possible lenses.

CONCLUSIONS:

~~~~~~~~~~~

Theoretical minimal size of a color sensor of sensitivity 1600ISO,

(which is equivalent to Velvia 50 36x24mm in resolution and noise)

is 13mm x 8.7mm. Similar B&W sensor can be 12x8mm. Likewise,

theoretical maximum sensitivity of 3/4'' 8MP color sensor is

1227 ISO.

[All intermediate numbers are given with quite high precision; of

course, due to approximations in assumptions, very few significant

digits are trustworthy.]

These numbers assume QE=1, and non-RGB sensor (to trade non-critical

chrominance noise vs. critical luminance noise). For example, in a

2x2 matrix one can have 2 cells with "white" (visible-transparent)

filter, 1 cell with yellow (passes R+G) filter, another with cyan

(passes G+B) filter.

ASSUMPTIONS:

~~~~~~~~~~~

a) Photopic curve can be well approximated by Gaussian curve

V(lambda) = 1.019 * exp( -285.4*(lambda-0.559)^2 )

see

http://home.tiscali.se/pausch/comp/radfaq.html

b) Solar irradiation spectrum on the sea level can be well approximated

by const/lambda in the visible spectrum (at least for the purpose

of integration of photopic curve). See

http://www.jgsee.kmutt.ac.th/exell/Solar/Intensity.html

http://www.clas.ufl.edu/users/emartin/GLY3074S03/images...

In the second one lower horizontal axis is obviously in nm, and the

upper one complete junk. Sigh...)

c) Sensitivity of the sensor is noise-bound. Thus sensitivity of

a cell of a sensor should be measured via certain noise level

at image of 18% gray at normal exposure for this sensitivity.

d) The values of noise given by Velvia 50 film and Canon 1D Mark II

at 800ISO setting at image of 18% gray are "acceptable". These

two are comparable, see

http://clarkvision.com/imagedetail/digital.signal.to.no...

Averaging 15 and 28 correspondingly, one gets 21.5 as the "acceptable"

value of S/N in the image of 18% gray.

e) Noise of the sensor is limited by the electron noise (Poisson noise

due to discrete values of charge); other sources of noise are

negligeable (with exposition well below 40sec). See

http://www.astrosurf.com/buil/d70v10d/eval.htm

f) The AE software in digital cameras is normalizing the signal so

that the image of 100% reflective gray saturates the sensor.

[from private communication of Roger Clark; used in "d"]

g) Normal exposure for 100ISO film exposes 18% gray at 0.08 lux-sec.

See

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00...

h) The color "equivalent resolution" numbers in

http://clarkvision.com/imagedetail/film.vs.digital.1.ht...

may be decrease by 25% to take into account recent (as of

2005) improvements in demosaicing algorithms. E.g., see

http://www.dpreview.com/reviews/konicaminoltaa200/page1...

Taking largest numbers (Velvia 50 again, and Tech Pan), this gives

16MP B&W sensor, and 12MP color sensor.

i) Eye is much less sensitive to the chrominance noise than to

luminance noise. Thus it makes sense to trade chrominance

noise if this improves luminance noise (up to some limits).

In particular, sensors with higher-transparency filter mask give

much lower luminance noise; the increased chrominance noise (due

to "large" elements in the to-RGB-translation matrix) does not

"spoil" the picture too much.

j) To estimate Poisson noise is very simple: to get S/N ratio K, one

needs to receive K^2 particles (electrons, or, assuming QE=1,

photons).

METAASSUMPTION

~~~~~~~~~~~~~~

In any decent photographic system the most important component

of performance/price ratio is the lenses. Since the price of the

lens scales as 4th or 5th power of its linear size, decreasing

the size of the sensor (while keeping S/N ratio) may lead to

very significant improvements of performance/price.

Details in the last section...

[This ignores completely the issue of the price of accumulated

"legacy" lenses, so is not fully applicable to professionals.]

Since sensor is purely electronic, so (more or less) subject to

Moore law, the theoretical numbers (which are currently an order

of magnitude off) have a chance to be actually relevant in not

so distant time. ;-)

PHOTON FLOW OF NORMAL EXPOSURE

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

First, we need to recalculate 0.08 lux-sec exposure into the the

photon flow.

Assume const/lambda energy spectral density (assumption b),

integration of photonic curve gives const*0.192344740294

filtered flow. With constant spectral density at

1 photon/(sec*mkm*m^2), const = h * c, so the eye-corrected energy

flow is 3.82082403851941e-20 W/m^2 = 2.60962281830876e-17 lux.

Thus 0.08 lux-sec corresponds to (constant) spectral density

3065.57711860622 photon/(mkm*mkm^2). This is the total photon flow

of the image of 18% gray normally exposed for 100ISO film.

B&W SENSOR

~~~~~~~~~~

One can imagine (among others) 3 different theoretical types of B&W

sensor: one giving "physiologically correct" response of the

photopic curve, one accepting all photons in the "extended visible"

range of the spectrum 380 to 780nm, and an intermediate one, one

accepting all photons in the "normal visible" range of the spectrum

400 to 700nm. See

http://en.wikipedia.org/wiki/Visible_light

To cover the first case, one needs to multiply the value obtained in

the previous section by the integral of the photopic curve,

0.106910937 mkm; for the other, one needs to multiply by the width

of the window, 0.4 mkm, and 0.3 mkm. Resulting values are

327.7437, 1226.23, and 919.673 photon/mkm^2 as the flow of 18% gray

normally exposed for 100ISO film.

However, since photopic curve should not produce any particularly

spectacular artistic effect, it makes sense to have the sensor

of maximal possible sensitivity, and achieve the photopic response

(if needed) by application of a suitable on-the-lens filter. So we

ignore the first value, and use the other two. For example, the

smaller value gives photon Poisson noise S/N ratio of 21.5 with a

square cell of 0.70896 mkm. The larger value of the window,

0.4 mkm, results in a square cell of 0.613977 mkm. These are

smallest possible sizes of the cell which can provide the required

S/N ratio at exposure suitable for 100ISO film.

To have 1600ISO sensor, these numbers should be quartupled; 16MP

3:2 ratio sensor based on the 0.4mkm spectral window results in

12x8mm sensor.

OPTIMIZING THE COLOR MASK

~~~~~~~~~~~~~~~~~~~~~~~~~

For color sensor, theoretical estimates are complicated by the

following issue: different collections of spectral curves for the

filter mask can result in identical sensor signal after suitable

post-processing. (This ignores noise, and de-mosaicing artefacts.)

Indeed, taking a linear combination of the R,G,B cells is equivalent

to substituting the transparency curves for mask filters by the

corresponding linear combination. (This assumes the linear

combination curve fits between 0 and 1.)

As we saw in B&W SENSOR section, a more transparent filter results

in higher S/N at the cell; if the filter is close to transparent,

cell's signal is close to luminance, thus higher transparency

results in improvement of luminance noise.

To estimate color reproduction, take spectral sensitivity curves

of the different types of sensors cells. Ideally, 3 linear

combinations of these curves should match the spectral sensitivity

curves of cones in human eyes. Assuming 3 different types of sensor

cells, this shows that spectral curves of cells should be linear

combinations of spectral sensitivity curves of cones. In

principle, any 3 independent linear combinations can be used for

sensors curves; recalculation to RGB requires just application of

a suitable matrix. However, large matrix coefficients will result

in higher chrominance noise. (Recall that we assume that [due to

high transparency] the luminance is quite close to signals

of the sensors, thus matrix coefficents corresponding to luminance

can't be large; thus all that large matrix coefficients can do is

to give contribution to CHROMINANCE noise.)

Without knowing exactly how eye reacts to chrominance and luminance

noise it is impossible to optimize the sensor structure; however,

one particular sensor structure is "logical" enough to be close to

optimal: take 2 filters in a 2x2 filter matrix to be as transparent

as possible while remaining a linear combination of cone curves.

This particular spectral curve is natural to call the W=R+G+B curve.

Take two other filters to be as far as possible from W (and

from each other) while keeping high transparency; in particular,

keep the most powerful (in terms of photon count) G channel, and

remove one of R and B channels; this may result, for example, in

the following filter matrix

W Y W Y W Y W Y

C W C W C W C W

W Y W Y W Y W Y

C W C W C W C W

here C=G+B, Y=R+G. Since the post-processing matrix R=W-C, B=W-G,

G=C+Y-W does not have large matrix coefficients, the increase in

chrominance noise is not significant.

Above, W means the combination of the cone sensitivity curves with

maximal integral among (physically possible) combinations with

"maximal transparency" being 1. While we cannot conclude that this

results in the optimal mask, recall the following elementary fact:

to estimate the maximal *value* f(x) one can make quite large errors

in the *argument* x, and still get good approximation for f(xMAX).

Thus choosing the matrix above gives a pessimistic estimate, AND one

should expect that it is not very far of the correct one.

TRANSPARENCY OF THE COLOR MASK

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Actually, what is R, G, B in colorimetry are in turn linear

combinations of responses of cones. Use cones sensitivity curves

from

http://www.rwc.uc.edu/koehler/biophys/6d.html

Now use RR, GG, and BB to denote *these* curves, not "usual" R, G, B

of colorimetry. Since I could not find these data in table form,

the values below are not maximal possible, but just first

opportunities which come to mind.

Using 0.9RR+0.35GG, one gets a quite flat curve; one may assume that

in range 0.42--0.65nm the sensitivity is above 0.9. with one at

700nm going down to 0.6, and 400nm going down to 0.8. So the

filter "compatible" with cone sensitivity curves can easily achive

0.9 transparency in the range 400--700nm, which would give photon

count 827.705822 photon/mkm^2 in the W (R+G+B) type cell. Taking

GG and 0.9RR+0.35BB curves as other types of sensors, one gets

average transparency about 0.8 and 0.85. Taking average

transparency of the filter over a 2x2 WCWY matrix cell 0.85, one

gets photon count averaged over different kinds of color-sensitive

cells as 781.722165 photon/mkm^2.

As above, we assume that this average photon count is the count

giving contribution into luminance noise.

FINAL ESTIMATES

~~~~~~~~~~~~~~~

With above average photon count at a cell, to get S/N ratio 21.5

one needs a square cell of 0.768975 mkm. Recall that this is the

the smallest possible cell which can provide the required S/N ratio

at exposure suitable for 100ISO film.

Quadrupling to get sensitivity 1600ISO, and taking 12MP equivalent

of 36x24mm Velvia 50, one gets the 13 x 8.7 mm sensor.

HOW GOOD CAN 36x34mm SENSOR GO?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In other direction, 36x24 mm color sensor at sensitivity 1600ISO can

(theoretically) be equivalent (or better) than 10 x 6.6 cm Velvia 50

film; that is 1/2 frame of 4x5 in film. In yet other words, take

36x24mm sensor with resolution and noise better than 4x5 Velvia 50

film; it has theoretical maximum of sensibility at 800ISO.

Likewise, to achieve resolution and noise of 8x10in Velvia 50 film,

the maximal sensibility of 36x24mm sensor is 200ISO.

THE QUESTION OF LENSES

~~~~~~~~~~~~~~~~~~~~~~

Of course, preceeding section completely ignores the issue of

lenses; on the other hand, a cheap prosumer zoom lens with

28--200mm equivalent paired with a digital sensor easily gives

resolution of 3.3mkm per single line (with usable image diameter

about 11mm, see

http://www.dpreview.com/reviews/konicaminoltaa200/page1...

); so we know it is practically possible to create a lens which

saturates the theoretical resolution of 1600ISO sensor (but probably

not 800ISO and 200ISO sensor!). It is natural to expect that a

non-zoom lens could saturate resolution of 800ISO sensor.

This gives theoretical resolution limit of a "practical" lens +

800ISO digital 36x24mm sensor: it is equivalent to best 4x5in 50ISO

film (with non-zoom lens). With zoom lense, one can achieve quality

of 2.5x4in 50ISO film; sensor is at 1600ISO, lense is 28-200mm zoom.

Some more estimates of how practical is "practical": the zoom

mentioned above is bundled with $600 street price camera which

weights about 580g. Assume the lens takes 1/2 of the price, and

1/4 of the weight. Rescaling from 11mm diagonal image size to the

36x24mm image size will increase price to $70K--$280K (assuming that

price is proportional to 4th-5th power of the size [these numbers

were applicable 20 years ago, I do not know what holds today]), and

will increase the weight to 9kg.

On the other hand, the 4:3 aspect ratio sensor of the same area as

the mentioned above 13 x 8.6 mm sensor (1600ISO sensor equivalent

in quality to Velvia 50 at 36x24mm) is 12.2 x 9.17mm, diagonal is

15.26mm. It is 0.9'' sensor (in the current - silly - notation).

Rescaling the mentioned above lens to this size gives lens price

$1100--$1500, and weight about 750g; both quite "reasonable".

Recall that this 28--200 equivalent zoom lens will saturates resolution

of an equivalent of Velvia 50 36x24mm film.

More about : long theoretical estimates film equivalent digital

Anonymous

March 6, 2005 11:50:37 AM

A very nice write up, I will admit I have not gone through all of it

yet in detail. One thing to consider is that CCD have a read out noise

of around 10 electrons, whereas this noise level will not greatly

effect the signal to noise when looking at 400 detected photons with an

noise level of 20 electrons it will start to dominate in darker parts

of the scene. For instance by the time you are down 5 stops from full

white the readout noise will be larger then the photon noise, by a

small amount.

The idea of using non-RGB filters is sound and a number of CCD sensors

have used filters more like C, Y and M. Why RGB is used on digital

cameras I am not sure.

Scott

Anonymous

March 9, 2005 3:52:16 AM

[A complimentary Cc of this posting was sent to

Scott W

<biphoto@hotmail.com>], who wrote in article <1110125916.657251.135140@z14g2000cwz.googlegroups.com>:

> A very nice write up, I will admit I have not gone through all of it

> yet in detail. One thing to consider is that CCD have a read out noise

> of around 10 electrons, whereas this noise level will not greatly

> effect the signal to noise when looking at 400 detected photons with an

> noise level of 20 electrons it will start to dominate in darker parts

> of the scene. For instance by the time you are down 5 stops from full

> white the readout noise will be larger then the photon noise, by a

> small amount.

This is a very valid remark. However, note that these were

*theoretical* estimates; after translation into this language your

remark becomes:

Readout noise should be decreased too; otherwise shadows noise is

going to be well above Poisson noise.

Thanks,

Ilya

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Anonymous

March 9, 2005 3:18:13 PM

Scott W <biphoto@hotmail.com> wrote:

> The idea of using non-RGB filters is sound and a number of CCD sensors

> have used filters more like C, Y and M. Why RGB is used on digital

> cameras I am not sure.

My guess is that to do otherwise would increase the chroma noise too

much. Chroma noise in digital cameras at high ISO is already

intrusive, and anything that increases it may be unwelcome, even if

sensitivity improved. Without direct experimental data it's hard to

say.

The other issue is how well non-RGB filters could be made to

approximate the colour matching functions of typical display systems.

Red and green are quite well matched by sensors of a typical camera,

but the blue is quite a way off because its spectral sensitivity is

too broad.[1] It would be a matter of measuring some physically

realizable filters and seeing what colour matching functions resulted.

Andrew.

[1] The Reproduction of Colour, 6th Edition, Robert Hunt, p556.

Anonymous

March 9, 2005 11:10:39 PM

Ilya Zakharevich wrote:

> PHOTON FLOW OF NORMAL EXPOSURE

> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

>

> First, we need to recalculate 0.08 lux-sec exposure into the the

> photon flow.

>

> Assume const/lambda energy spectral density (assumption b),

> integration of photonic curve gives const*0.192344740294

> filtered flow. With constant spectral density at

> 1 photon/(sec*mkm*m^2), const = h * c, so the eye-corrected energy

> flow is 3.82082403851941e-20 W/m^2 = 2.60962281830876e-17 lux.

What unit is 'mkm', wavenumber?

-- Hans

Anonymous

March 10, 2005 12:28:43 PM

[A complimentary Cc of this posting was sent to

<andrew29@littlepinkcloud.invalid>], who wrote in article <112tqc5260hi724@news.supernews.com>:

> My guess is that to do otherwise would increase the chroma noise too

> much. Chroma noise in digital cameras at high ISO is already

> intrusive, and anything that increases it may be unwelcome, even if

> sensitivity improved. Without direct experimental data it's hard to

> say.

When I look on the digital images of a gray surface (those of "compare

two cameras" kind), it looks like my perception of noise is not

related to chrominance noise at all. At least a camera with higher

measured individual-channel R/G/B noise can produce much lower visible

noise if its noise reduction algorithm favors luminance noise (as

confirmed by luminance noise graph). Of course, it is in no way

scientific conclusion, but I may have seen about ten such

comparisons...

> The other issue is how well non-RGB filters could be made to

> approximate the colour matching functions of typical display

> systems.

AFAIU, this has nothing to do with display (output) system, but only

with input system (cones). As far as the filters match cones, you can

postprocess colors into *any* display system (if the initial color is

in the gamut of the display system).

And if you do not match the cone sensitivity, colors which look the

same will get different when stored. After this no amount of

post-processing will be able to fix this.

Hope this helps,

Ilya

Anonymous

March 10, 2005 12:32:28 PM

[A complimentary Cc of this posting was sent to

HvdV

<nohanz@svi.nl>], who wrote in article <3059$422f4a27$3e3aaa83$633@news.versatel.net>:

> > filtered flow. With constant spectral density at

> > 1 photon/(sec*mkm*m^2), const = h * c, so the eye-corrected energy

> > flow is 3.82082403851941e-20 W/m^2 = 2.60962281830876e-17 lux.

> What unit is 'mkm', wavenumber?

Yes (?); Wavelength. IIRC, wavenumber is 1/wavelength (or some such;

2pi comes to mind...).

[BTW, because of non-linearity of wavelength vs wavenumber, spectral

density which constant per wavelength becomes very non-constant when

measured per wavenumber.]

Yours,

Ilya

Anonymous

March 11, 2005 6:39:49 AM

andrew29@littlepinkcloud.invalid writes:

>[1] The Reproduction of Colour, 6th Edition, Robert Hunt, p556.

I didn't realize that the 6th edition was out. Does it say how it

differs from the previous edition (e.g. in a preface?).

I do have the 3rd, 4th, and 5th editions already, but they don't cover

digital imaging much.

Dave

Anonymous

March 12, 2005 12:37:57 AM

Hi Ilya,

>

>

> Yes (?); Wavelength. IIRC, wavenumber is 1/wavelength (or some such;

> 2pi comes to mind...).

Yes, wavenumber is 2 * pi / lambda, units m^-1

>

> [BTW, because of non-linearity of wavelength vs wavenumber, spectral

> density which constant per wavelength becomes very non-constant when

> measured per wavenumber.]

Yes, but the choice is arbitrary. Since wavenumber which is proportional to

photon energy, an interesting quantity for many applications, spectroscopy

people tend towards wavenumber whereas optical people like wavelength since

resolving power scales with that.

BTW, can you substantiate your interesting assumption:

----

In any decent photographic system the most important component

of performance/price ratio is the lenses. Since the price of the

lens scales as 4th or 5th power of its linear size, decreasing

the size of the sensor (while keeping S/N ratio) may lead to

very significant improvements of performance/price.

---

with some examples?

The tradeoff of lens aperture and expense vs sensor size determines

ultimately the size and shape of the digital camera. After the 'fashion

factor' of course.

-- hans

Anonymous

March 12, 2005 10:12:34 PM

[A complimentary Cc of this posting was sent to

<andrew29@littlepinkcloud.invalid>], who wrote in article <112tqc5260hi724@news.supernews.com>:

> Scott W <biphoto@hotmail.com> wrote:

> > The idea of using non-RGB filters is sound and a number of CCD sensors

> > have used filters more like C, Y and M. Why RGB is used on digital

> > cameras I am not sure.

>

> My guess is that to do otherwise would increase the chroma noise too

> much. Chroma noise in digital cameras at high ISO is already

> intrusive, and anything that increases it may be unwelcome, even if

> sensitivity improved. Without direct experimental data it's hard to

> say.

Judge for yourself: visit

http://ilyaz.org/photo/random-noise

Yours,

Ilya

Anonymous

March 12, 2005 10:26:06 PM

[A complimentary Cc of this posting was sent to

HvdV

<nohanz@svi.nl>], who wrote in article <7ac8b$4232019c$3e3aaa83$3472@news.versatel.net>:

> In any decent photographic system the most important component

> of performance/price ratio is the lenses. Since the price of the

> lens scales as 4th or 5th power of its linear size, decreasing

> the size of the sensor (while keeping S/N ratio) may lead to

> very significant improvements of performance/price.

> ---

> with some examples?

> The tradeoff of lens aperture and expense vs sensor size determines

> ultimately the size and shape of the digital camera. After the 'fashion

> factor' of course.

a) First of all, my assumption on how rescaling the lense affects

image quality was "incomplete" (read: wrong ;-). Part of fuzziness

due to difraction does not change; but part of fuzziness due to

optical imperfection scales up with the lense linear size (since

all the light rays passing through the system scale up, the spot in

the focal plane which is the diffraction-less image of a

point-source will scale up as well).

This has two effects: sweet spot (in F-stops) scales up (i.e., to

the worse) as sqrt(size); and best resolution scales down as

1/sqrt(size). So my estimates for "perfect lense" for an ideal

36x24mm sensor were wrong, since I erroneously assumed that the

sweet spot does not change.

b) One corollary is that when you scale sensor size AND LENSE up n

times, it makes sense to scale up the size of the pixel sqrt(n)

times. In other words, you should increase the sensitivity of the

sensor and number of pixels both the same amount - n times.

Interesting...

c) The estimages on price vs. size: IIRC, this was from a review in a

technical magazine on optical production ("Scientific publications

of LOMO" or some such) in end of 80s. Since technology could have

changed meanwhile (digitally-controlled machinery?), the numbers

could have changed...

Hope this helps,

Ilya

Anonymous

March 12, 2005 10:27:17 PM

Ilya Zakharevich wrote:

[]

> Judge for yourself: visit

>

> http://ilyaz.org/photo/random-noise

>

> Yours,

> Ilya

Grey is one colour to test this on - what about a more sensitive colour

like skin-tones?

Cheers,

David

Anonymous

March 12, 2005 11:46:33 PM

[A complimentary Cc of this posting was sent to

David J Taylor

<david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk>], who wrote in article <poHYd.3079$QN1.2097@text.news.blueyonder.co.uk>:

> > Judge for yourself: visit

> >

> > http://ilyaz.org/photo/random-noise

> Grey is one colour to test this on - what about a more sensitive colour

> like skin-tones?

The script is there. Feel free to edit it to change the base value.

Or just modify the .png by adding a constant bias...

Yours,

Ilya

Anonymous

March 13, 2005 4:22:13 AM

[A complimentary Cc of this posting was sent to

Scott W

<biphoto@hotmail.com>], who wrote in article <1110125916.657251.135140@z14g2000cwz.googlegroups.com>:

> A very nice write up, I will admit I have not gone through all of it

> yet in detail. One thing to consider is that CCD have a read out noise

> of around 10 electrons, whereas this noise level will not greatly

> effect the signal to noise when looking at 400 detected photons with an

> noise level of 20 electrons it will start to dominate in darker parts

> of the scene. For instance by the time you are down 5 stops from full

> white the readout noise will be larger then the photon noise, by a

> small amount.

On the second thought, maybe this issue is not as crucial as it may

sound. Remember that 12 electrons noise is present on Mark II, and

its 800ISO setting is "considered nice". It has S/N=28 at Zone V; so

the electron noise at Zone III should be about 13 electrons; while 12

electrons readout noise will increase this to total about 17

electrons, we must conclude that such a noise (S/N=9) at Zone III is

not very bad. Likewise for Zones II and I.

So: either Mark II produces noticable noise in zones I--III, or

readout noise 12 electrons is already small enough to be "not

important".

Yours,

Ilya

Anonymous

March 13, 2005 4:30:37 AM

[A complimentary Cc of this posting was NOT [per weedlist] sent to

Ilya Zakharevich

<nospam-abuse@ilyaz.org>], who wrote in article <d0vkf9$1io5$1@agate.berkeley.edu>:

> > > Judge for yourself: visit

> > > http://ilyaz.org/photo/random-noise

> > Grey is one colour to test this on - what about a more sensitive colour

> > like skin-tones?

> The script is there. Feel free to edit it to change the base value.

> Or just modify the .png by adding a constant bias...

Actually, it may be a little bit more than just changing the base

value. Luminance is calculatable from Luma only very close to neutral

gray; thus having a skin-tone with luma-less noise may have

significant luminance noise.

One needs to experiment with both constant-luma noise and

constant-luminance noise, and see which one is less perceivable by

eye. Summary: one may need also to modify the vector 0.2126 0.7152

0.0722 to take into account gamma (via derivatives of x^2.2 at R'G'B'

values of skin tone).

Yours,

Ilya

Paul

March 13, 2005 4:30:38 AM

Ilya Zakharevich wrote:

>

>>>>Judge for yourself: visit

>

>

>>>> http://ilyaz.org/photo/random-noise

>

>

> ...Luminance is calculatable from Luma only very close to neutral

> gray; thus having a skin-tone with luma-less noise may have

> significant luminance noise.

>

> One needs to experiment with both constant-luma noise and

> constant-luminance noise, and see which one is less perceivable by

> eye. Summary: one may need also to modify the vector 0.2126 0.7152

> 0.0722 to take into account gamma (via derivatives of x^2.2 at R'G'B'

> values of skin tone).

Any chance of an executive summary of this study. I just cannot see what

the exercise is all about.

The photoshop RAW converter has color (chrominance) & regular

(luminance) noise reduction & I noticed the color noise reduction does

almost nothing. It seems you are saying color noise is indeed

insubstantial in comparison but maybe I'm missing the boat on that?

thanks!

Anonymous

March 13, 2005 12:34:50 PM

Ilya Zakharevich wrote:

> [A complimentary Cc of this posting was NOT [per weedlist] sent to

> Ilya Zakharevich

> <nospam-abuse@ilyaz.org>], who wrote in article

> <d0vkf9$1io5$1@agate.berkeley.edu>:

>>>> Judge for yourself: visit

>

>>>> http://ilyaz.org/photo/random-noise

>

>>> Grey is one colour to test this on - what about a more sensitive

>>> colour like skin-tones?

>

>> The script is there. Feel free to edit it to change the base value.

>> Or just modify the .png by adding a constant bias...

>

> Actually, it may be a little bit more than just changing the base

> value. Luminance is calculatable from Luma only very close to neutral

> gray; thus having a skin-tone with luma-less noise may have

> significant luminance noise.

>

> One needs to experiment with both constant-luma noise and

> constant-luminance noise, and see which one is less perceivable by

> eye. Summary: one may need also to modify the vector 0.2126 0.7152

> 0.0722 to take into account gamma (via derivatives of x^2.2 at R'G'B'

> values of skin tone).

>

> Yours,

> Ilya

Thanks, Ilya. I don't have the time to do detailed work on this right

now, but at least I hope it triggers /someone/ to check this out. Your

comments about the gamma remind me of the "constant luminance failure"

errors in colour TV - takes me back a long time.

http://www.poynton.com/notes/video/Constant_luminance.h...

Cheers,

David

Anonymous

March 13, 2005 10:39:26 PM

[A complimentary Cc of this posting was sent to

paul

<paul@not.net>], who wrote in article <8bSdnaijPZrUXa7fRVn-sg@speakeasy.net>:

> >>>>Judge for yourself: visit

> >>>> http://ilyaz.org/photo/random-noise

> Any chance of an executive summary of this study. I just cannot see what

> the exercise is all about.

Did you see the pictures on the URL above?

> The photoshop RAW converter has color (chrominance) & regular

> (luminance) noise reduction & I noticed the color noise reduction does

> almost nothing. It seems you are saying color noise is indeed

> insubstantial in comparison but maybe I'm missing the boat on that?

How I see the pictures, the eye sensitivity for chrominance noise is

not much higher than 10% of sensitivity for luminance one. [But my

eyes are kinda special, so I would appreciate if somebody else - with

normal vision - confirms this.]

Yours,

Ilya

Paul

March 13, 2005 10:39:27 PM

Ilya Zakharevich wrote:

> [A complimentary Cc of this posting was sent to

> paul

> <paul@not.net>], who wrote in article <8bSdnaijPZrUXa7fRVn-sg@speakeasy.net>:

>

>>>>>>Judge for yourself: visit

>

>

>>>>>>http://ilyaz.org/photo/random-noise

>

>

>>Any chance of an executive summary of this study. I just cannot see what

>>the exercise is all about.

>

>

> Did you see the pictures on the URL above?

>

>

>>The photoshop RAW converter has color (chrominance) & regular

>>(luminance) noise reduction & I noticed the color noise reduction does

>>almost nothing. It seems you are saying color noise is indeed

>>insubstantial in comparison but maybe I'm missing the boat on that?

>

>

> How I see the pictures, the eye sensitivity for chrominance noise is

> not much higher than 10% of sensitivity for luminance one. [But my

> eyes are kinda special, so I would appreciate if somebody else - with

> normal vision - confirms this.]

So that's equal noise on left & right? No doubt the left looks 90% more

noisy. I suppose if I zoomed way in, I could see the color noise.

Anonymous

March 14, 2005 3:03:32 AM

Hi Ilya,

> [A complimentary Cc of this posting was sent to

> HvdV

> <nohanz@svi.nl>], who wrote in article <7ac8b$4232019c$3e3aaa83$3472@news.versatel.net>:

Substitute 'hans' for 'nohanz', sorry for the paranoia.

>>In any decent photographic system the most important component

>>of performance/price ratio is the lenses. Since the price of the

>>lens scales as 4th or 5th power of its linear size, decreasing

>>the size of the sensor (while keeping S/N ratio) may lead to

>>very significant improvements of performance/price.

>>---

>>with some examples?

>>The tradeoff of lens aperture and expense vs sensor size determines

>>ultimately the size and shape of the digital camera. After the 'fashion

>>factor' of course.

>

>

> a) First of all, my assumption on how rescaling the lense affects

> image quality was "incomplete" (read: wrong ;-). Part of fuzziness

> due to difraction does not change; but part of fuzziness due to

> optical imperfection scales up with the lense linear size (since

> all the light rays passing through the system scale up, the spot in

> the focal plane which is the diffraction-less image of a

> point-source will scale up as well).

>

> This has two effects: sweet spot (in F-stops) scales up (i.e., to

> the worse) as sqrt(size); and best resolution scales down as

> 1/sqrt(size). So my estimates for "perfect lense" for an ideal

> 36x24mm sensor were wrong, since I erroneously assumed that the

> sweet spot does not change.

Hm, not so sure you were very wrong. I don't know much about lens design, but

I do know errors like spherical aberration scale up in a non-linear fashion

if you increase aperture. And that's only one of the many errors.

Then there are amplifying econimical factors like a much smaller lens copy

number.

BTW, if you keep aperture constant the diffraction spot stays the same. It

scales with the wavelength, the sine of the half-aperture angle, and for

completeness, also the refractive index of the medium.

>

> b) One corollary is that when you scale sensor size AND LENSE up n

> times, it makes sense to scale up the size of the pixel sqrt(n)

> times. In other words, you should increase the sensitivity of the

> sensor and number of pixels both the same amount - n times.

> Interesting...

Sizing up the lens and sensor gets you more information about the object,

with the square of the scale. You can average that information with bigger

pixels to get a better SNR, but you could do that also in postprocessing.

>

> c) The estimages on price vs. size: IIRC, this was from a review in a

> technical magazine on optical production ("Scientific publications

> of LOMO" or some such) in end of 80s. Since technology could have

> changed meanwhile (digitally-controlled machinery?), the numbers

> could have changed...

It's clear that it is cheaper now to make aspherical lenses, and there are

also new glasses available.

I was hoping for a plot with a lenses with similar view angles in it with on

the horizontal axis the formats and vertically the price. I guess it should

be possible to dig this out of ebay..

-- Hans

Anonymous

March 15, 2005 12:54:34 AM

[A complimentary Cc of this posting was sent to

paul

<paul@not.net>], who wrote in article <Mp-dnSpYkaAxA6nfRVn-3Q@speakeasy.net>:

> > How I see the pictures, the eye sensitivity for chrominance noise is

> > not much higher than 10% of sensitivity for luminance one. [But my

> > eyes are kinda special, so I would appreciate if somebody else - with

> > normal vision - confirms this.]

> So that's equal noise on left & right? No doubt the left looks 90% more

> noisy.

You mean "LESS noisy"?

No, it is not "equal noise". I'm afraid you need to read the

explanation at the beginning. In addition to "equal noise" having

little sense, as you can easily see, the noise on the right is

*different* at top and at bottom.

But numerical noise on the left "is close" to numerical noise on the

bottom of the right. Visual noise is an order of magnitude less...

Yours,

Ilya

Anonymous

March 15, 2005 1:06:19 AM

[A complimentary Cc of this posting was sent to

HvdV

<nohanz@svi.nl>], who wrote in article <91fe8$4234c6bb$3e3aaa83$31509@news.versatel.net>:

> Hm, not so sure you were very wrong. I don't know much about lens design, but

> I do know errors like spherical aberration scale up in a non-linear fashion

> if you increase aperture.

Sure, but I was not talking about increase of aperture. I was talking

about using the same lense design *geometrically rescaled* for larger

sensor size.

> BTW, if you keep aperture constant the diffraction spot stays the same. It

> scales with the wavelength, the sine of the half-aperture angle, and for

> completeness, also the refractive index of the medium.

Yes, this is what I wrote (not in so many words, though ;-).

> > b) One corollary is that when you scale sensor size AND LENSE up n

> > times, it makes sense to scale up the size of the pixel sqrt(n)

> > times. In other words, you should increase the sensitivity of the

> > sensor and number of pixels both the same amount - n times.

> > Interesting...

> Sizing up the lens and sensor gets you more information about the object,

> with the square of the scale. You can average that information with bigger

> pixels to get a better SNR, but you could do that also in postprocessing.

It does not always make sense to do it in postprocessing; in absense

of readout noise more pixels can be recalculated in less pixel

losslessly, but I'm not sure that it is easy to reduce readout noise...

Even without readout noise, assuming that it does not make sense to

rasterize at resolution (e.g.) 3 times higher than the resolution of

the lense, when you rescale your lense+sensor (keeping the lense

design), you better rescale the pixel count and sensitivity the same

amount.

[Additional assumption: the sweet spot is not better than the maximal

aperture of the lense. E.g., the current prosumer 8MP lenses have the

sweet spot at maximal aperture; so if you rescale this design *down*,

the law above does not hold. BTW, rescaling them up from 2/3'' sensor

to 36x24mm sensor (3.93x rescale) will give, e.g., 28--200 F2.8 zoom

with corner-to-corner high resolution and sweet spot at 5.6.]

Yours,

Ilya

Anonymous

March 16, 2005 2:03:25 AM

Ilya Zakharevich wrote:

>

> Sure, but I was not talking about increase of aperture. I was talking

> about using the same lense design *geometrically rescaled* for larger

> sensor size.

Sorry for making myself not clear, what I meant was that if you scale up,

keeping aperture angle constant, aberrations will act up. Suppose for a small

lens you have a manageable deviation from a spherical wave of Pi/4 phase

error, then for a twice larger system parts of the wave will arrive out of

phase at the focus, seriously affecting your resolution. Likely the error is

due to production flaws and imperfect design. To force back the phase error

both the production techniques and the design must be improved. That suggests

that your earlier assumption of steeply rising production cost are true.

If you compare 35mm to MF lenses you see that for the same view angle lenses

tend to have higher f-numbers and are much more expensive, 4x?

>

>

> It does not always make sense to do it in postprocessing; in absense

> of readout noise more pixels can be recalculated in less pixel

> losslessly, but I'm not sure that it is easy to reduce readout noise...

CCDs for low light applications are usually capable of binning pixels to get

around this. I don't know whether this technique is used in any camera.

>

> Even without readout noise, assuming that it does not make sense to

> rasterize at resolution (e.g.) 3 times higher than the resolution of

> the lense, when you rescale your lense+sensor (keeping the lense

> design), you better rescale the pixel count and sensitivity the same

> amount.

When readout noise is not a key factor it is IMO better to match the pixel

size to the optical bandwidth, making anti aliasing filters superfluous. With

all the image information in your computer it's then up to the post

processing to figure out what the image was. Just my hobby horse...

>

> [Additional assumption: the sweet spot is not better than the maximal

> aperture of the lense. E.g., the current prosumer 8MP lenses have the

> sweet spot at maximal aperture; so if you rescale this design *down*,

> the law above does not hold. BTW, rescaling them up from 2/3'' sensor

Nice point!

But instead of cheaper scaling down makes more outrageous designs possible

for the same price, in particular larger zoom ranges with similar apertures.

This leads to the feature battle where manufacturers advertise the MP number

and the zoom range.

> to 36x24mm sensor (3.93x rescale) will give, e.g., 28--200 F2.8 zoom

> with corner-to-corner high resolution and sweet spot at 5.6.]

If you scale up the 28--200 F2.0--F2.8 on the Sony 828 to 35mm you get indeed

something unaffordable.

-- Hans

Anonymous

March 16, 2005 2:03:26 AM

[A complimentary Cc of this posting was sent to

HvdV

<nohanz@svi.nl>], who wrote in article <42375BAD.8080906@svi.nl>:

> > Sure, but I was not talking about increase of aperture. I was talking

> > about using the same lense design *geometrically rescaled* for larger

> > sensor size.

> Sorry for making myself not clear, what I meant was that if you

> scale up, keeping aperture angle constant, aberrations will act

> up. Suppose for a small lens you have a manageable deviation from a

> spherical wave of Pi/4 phase error, then for a twice larger system

> parts of the wave will arrive out of phase at the focus, seriously

> affecting your resolution.

I think we speak about the same issue using two different languages:

you discuss wave optic, I - geometric optic. You mention pi/4 phase,

I discuss "the spot" where rays going through different places on the

lense come to.

Assume that "wave optic" = "geometric optic" + "diffration". Under

this assumption (which I used) your "vague" discription is

*quantified* by using the geometric optic language: "diffration"

"circle" does not change when you scale, while "geometric optic" spot

grows linearly with the size. This also quantifies the dependence of

the "sweet spot" and maximal resolution (both changing with

sqrt(size)).

So if the assumption holds, my approach is more convenient. ;-) And,

IIRC, it holds in most situations. [I will try to remember the math

behind this.]

> Likely the error is due to production flaws and imperfect design. To

> force back the phase error both the production techniques and the

> design must be improved. That suggests that your earlier assumption

> of steeply rising production cost are true.

Let us keep these two issues separate (as a customer in a restorant

said: may I have soup separate and cockroaches separate?). Rescaling

of a *design* leads to sqrt(size) increase in sweet spot; rescaling of

*defects w.r.t. design* leads to steep cost-vs-size curve...

> > Even without readout noise, assuming that it does not make sense to

> > rasterize at resolution (e.g.) 3 times higher than the resolution of

> > the lense, when you rescale your lense+sensor (keeping the lense

> > design), you better rescale the pixel count and sensitivity the same

> > amount.

> When readout noise is not a key factor it is IMO better to match the

> pixel size to the optical bandwidth, making anti aliasing filters

> superfluous.

I assume that "matching" is as above: having sensor resolution "K

times the lense resolution", for some number K? IIRC, military air

reconnaissance photos were (Vietnam era?) scanned several times above

the optical resolution, and it mattered. [Likewise for this 700 MP IR

telescope?] Of course, increasing K you hit a return-of-investment

flat part pretty soon, this is why I had chosen this low example value

"3" above...

> > [Additional assumption: the sweet spot is not better than the maximal

> > aperture of the lense. E.g., the current prosumer 8MP lenses have the

> > sweet spot at maximal aperture; so if you rescale this design *down*,

> > the law above does not hold. BTW, rescaling them up from 2/3'' sensor

> Nice point!

> But instead of cheaper scaling down makes more outrageous designs possible

> for the same price, in particular larger zoom ranges with similar apertures.

> This leads to the feature battle where manufacturers advertise the MP number

> and the zoom range.

AFAIU, the current manufacturing gimmic is dSLRs. [If my analysis is

correct] in a year or two one can have a 1'' sensor with the same

performance as Mark II (since sensors with QE=0.8 are in production

today, all you need is to scale the design to 12MP, and use "good"

filter matrix). This would mean the 35mm world switching to lenses

which are 3 times smaller, 25 times lighter, and 100 times cheaper (or

correspondingly, MUCH MUCH better optic).

My conjecture is that today the marketing is based on this "100 times

cheaper" dread. The manufacturers are trying to lure the public to

buy as many *current design* lenses as possible; they expect that

these lenses are going to be useless in a few years, so people will

need to change their optic again.

[While for professionals, who have tens K$ invested in lenses, dSLRs

are very convenient, for Joe-the-public the EVFs of today are much

more practical; probably producers use the first fact to confuse the

Joes to by dSLRs too; note the stop of the development of EVF during

the last 1/2 year, when they reached the spot they start to compete

with dSLR, e.g., KM A200 vs A2 down-grading.]

This is similar to DVDs today: during last several months, when

blue-rays are at sight, studios started to digitize films as if there

is no tomorrow...

Thanks for a very interesting discussion,

Ilya

Anonymous

March 23, 2005 12:09:28 AM

This discussion got a little bit too long. Here is a short summary.

A lot of people confuse counting photons with counting electrons.

This leads to statements like Roger Clark's

"these high-end cameras are reaching the limits of what

is possible from a theoretically perfect sensor."

Actually, even with sensor technology available now (for

mass-production), the sensitivity of the sensor he

considers can be improved 4.8 times; or the size can be

decreased 2.2 times without affecting MP count, sensitivity, and

noise.

Perfect Bayer filter sensors have equivalent film sensitivity of

12000 ISO (taking noise and resolution of Velvia 50 film as a

reference point). In other words, with such a sensor you get

equivalent resolution and noise of Velvia 50 film with 240 times

smaller exposure. For example, for 36x24mm format one gets a

12Mpixels sensor with 8.5 mkm square sensels with sensitivity

12000 ISO (calculated to achieve noise level better than one

of Velvia 50).

One illustration: since shooting with aperture smaller than F/16 does

not fully use the resolution of 8.5mkm sensels, for best results one

should use daylight exposure similar to F/16, 1/12000sec. (Of

course, one can lower the sensitivity of the sensor also by

controling the ADC; this would decrease the noise. E.g.,

decreasing the sensibility 8 times, one can achieve the noise

of a best-resolution 8x10in shot. However, I did not see any

indication that noise well below one given by Velvia 50 on 35mm

film results in any improvement of the image...)

Another illustration: the 8Mpixels sensor of EOS 1D Mark II (recall

that it achieves the noise level of Velvia 50 at sensitivity on or

above 1200ISO) has the "total" Quantum Efficiency about 14.1%.

The "total" efficiency of "the sensor assembly" is the product of

average "quantum efficiency" (in other words, transparency) of the

cells of the Bayer filter, and the quantum efficiency of the actual

sensor. To distinguish colors, some photons MUST be captured by the

Bayer filter; however, it is easy to design a filter with average

transparency 85% or above. On the other hand, currently there are

mass-produced sensors with QE=0.8; combining such a sensor with such

a filter, one can get the "total" efficiency of 68%. Thus the

sensitivity of the sensor of EOS 1D Mark II can be improved 4.8 times

without using any new technology...

The last illustration: using the same value QE=0.8, a 12MP sensor

of size 8.8x6.6mm (this is a 2/3'' sensor) has sensitivity of

655ISO. (Again, this is with better resolution and noise than

35mm Velvia 50!)

Recall that 2/3'' format is especially nice, since an affordable

lense in this format should provide the same resolution as a very

expensive lense in 35mm format. For example, compare a 35mm zoom

having the sweet spot at f/11 with a 2/3'' zoom having the sweet

spot at f/2.8; they have the same resolution at their sweet spots.

Recall also that the 2/3'' lenses have the same depth of field,

much larger zoom range, allow 4x shorter exposure at the same

resolution, and due to 4x smaller size are much easier to

image-stabilize on the sensor level.

P.S. One of the conclusions I make is that nowadays it does not makes

sense to ask for equivalent of digicams in terms of film cameras.

35mm film is not good enough to use the full potential of decent

35mm lenses; very soon it will be possible to produce affordable

sensors which will be able to exhaust potentials of these lenses.

It makes more sense to ask what kind of sensor "suits most"

a particular lense...

Ilya

Anonymous

March 23, 2005 1:26:09 AM

In article <d1q1i8$24rq$1@agate.berkeley.edu>, Ilya Zakharevich says...

> The "total" efficiency of "the sensor assembly" is the product of

> average "quantum efficiency" (in other words, transparency) of the

> cells of the Bayer filter, and the quantum efficiency of the actual

> sensor. To distinguish colors, some photons MUST be captured by the

> Bayer filter; however, it is easy to design a filter with average

> transparency 85% or above. On the other hand, currently there are

> mass-produced sensors with QE=0.8; combining such a sensor with such

> a filter, one can get the "total" efficiency of 68%. Thus the

> sensitivity of the sensor of EOS 1D Mark II can be improved 4.8 times

> without using any new technology...

Are you talking of front-illuminated or back-illuminated CCDs here ?

--

Alfred Molon

------------------------------

Olympus 4040, 5050, 5060, 7070, 8080, E300 forum at

http://groups.yahoo.com/group/MyOlympus/

Olympus 8080 resource - http://myolympus.org/8080/

Anonymous

March 23, 2005 1:26:10 AM

[A complimentary Cc of this posting was sent to

Alfred Molon

<alfredREMOVE_molon@yahoo.com>], who wrote in article <MPG.1caaabdc6f415c6c98aa61@news.supernews.com>:

> In article <d1q1i8$24rq$1@agate.berkeley.edu>, Ilya Zakharevich says...

>

> > The "total" efficiency of "the sensor assembly" is the product of

> > average "quantum efficiency" (in other words, transparency) of the

> > cells of the Bayer filter, and the quantum efficiency of the actual

> > sensor. To distinguish colors, some photons MUST be captured by the

> > Bayer filter; however, it is easy to design a filter with average

> > transparency 85% or above. On the other hand, currently there are

> > mass-produced sensors with QE=0.8; combining such a sensor with such

> > a filter, one can get the "total" efficiency of 68%. Thus the

> > sensitivity of the sensor of EOS 1D Mark II can be improved 4.8 times

> > without using any new technology...

>

> Are you talking of front-illuminated or back-illuminated CCDs here ?

Actually, what I saw was that both CCDs and CMOSes can "now" (it was

in papers of 2003 or 2004) achieve QE of 80%. Do not remember whether

it was front- or back- for CCDs; probably back-. However, my first

impression was that front- with microlenses can give the same

performance as back-, does not it?

Yours,

Ilya

Anonymous

March 23, 2005 1:17:38 PM

In article <d1q4s5$25qu$1@agate.berkeley.edu>, Ilya Zakharevich says...

> > Are you talking of front-illuminated or back-illuminated CCDs here ?

>

> Actually, what I saw was that both CCDs and CMOSes can "now" (it was

> in papers of 2003 or 2004) achieve QE of 80%. Do not remember whether

> it was front- or back- for CCDs; probably back-. However, my first

> impression was that front- with microlenses can give the same

> performance as back-, does not it?

Usually front-illuminated CCDs have QEs in the range 20-30%, while back-

illuminated ones have QEs up to 100%.

--

Alfred Molon

------------------------------

Olympus 4040, 5050, 5060, 7070, 8080, E300 forum at

http://groups.yahoo.com/group/MyOlympus/

Olympus 8080 resource - http://myolympus.org/8080/

Anonymous

March 24, 2005 1:18:35 AM

[A complimentary Cc of this posting was sent to

Alfred Molon

<alfredREMOVE_molon@yahoo.com>], who wrote in article <MPG.1cab529fc45c40ee98aa63@news.supernews.com>:

> > Actually, what I saw was that both CCDs and CMOSes can "now" (it was

> > in papers of 2003 or 2004) achieve QE of 80%. Do not remember whether

> > it was front- or back- for CCDs; probably back-. However, my first

> > impression was that front- with microlenses can give the same

> > performance as back-, does not it?

> Usually front-illuminated CCDs have QEs in the range 20-30%, while back-

> illuminated ones have QEs up to 100%.

Thanks; probably I was not paying enough attention when reading these

papers. Anyway, I also saw this 100% number quoted in many places,

but the actual graphs of QE/vs/wavelength presented in the papers were

much closer to 80%...

Anyway, I would suppose that of these 4.84 which are the current

inefficiency (comparing to QE=0.8 sensor with a good Bayer matrix), at

least about 2..3 comes from using RGB Bayer (and I do not have a

slightest idea why they use RGB). This gives the QE of the "actual"

sensor closer to 30..40%. This is a kinda strange number - too good

for front-, too bad for back-. [Of course, the actual sensor is CMOS

;-]

Are there actual back-illumination sensor used in mass-production

digicams?

Thanks,

Ilya

Anonymous

March 24, 2005 3:51:07 PM

In article <d1spvr$2qj8$1@agate.berkeley.edu>, Ilya Zakharevich says...

> Are there actual back-illumination sensor used in mass-production

> digicams?

To my knowledge no - they are all used for astronomy. The production

process involves thinning the CCD to around 10 micrometer (or something

very thin). Then the back side of the CCD, which does not have all

layers with the circuitry which would obstruct light, is used as the

active side. But either the additional production process is expensive

or the resulting CCDs are too thin for mass production. Try doing a

Google search for "back illuminated CCDs".

--

Alfred Molon

------------------------------

Olympus 4040, 5050, 5060, 7070, 8080, E300 forum at

http://groups.yahoo.com/group/MyOlympus/

Olympus 8080 resource - http://myolympus.org/8080/

Anonymous

April 1, 2005 2:31:36 AM

Hi Ilya,

(took me a while to come back to this topic)

>

> I think we speak about the same issue using two different languages:

> you discuss wave optic, I - geometric optic. You mention pi/4 phase,

> I discuss "the spot" where rays going through different places on the

> lense come to.

>

> Assume that "wave optic" = "geometric optic" + "diffration". Under

> this assumption (which I used) your "vague" discription is

> *quantified* by using the geometric optic language: "diffration"

> "circle" does not change when you scale, while "geometric optic" spot

> grows linearly with the size. This also quantifies the dependence of

> the "sweet spot" and maximal resolution (both changing with

> sqrt(size)).

You can use geometrical optics to compute optical path lengths from an object

to any location behind the lens, but to find out what intensity you get there

you need to sum all light contributing to that point and take its phase into

account.

The point I tried to make earlier is that the geometry scales, but the

wavelength doesn't, so scaling up means scaling up phase errors. Take for

example a phase error caused by spherical aberration (SA) between rays

through the center of the lens and those from the rim, causing the rim-rays

to be focused in front of the focal plane. Doubling the phase error will at

least double that distance, depending on the aperture angle. To understand

the wild pattern created by all interphering phase shifted rays you need to

do that summation mentioned above. All in all this causes quite non-linear

effects on the 2D spot size as you scale the lens, but also seriously affects

its out off focus 3D shape, related to the bokeh.

If at the sweet spot (measured in f/d number) the size of the diffraction

spot balances against geometrical errors like chromatic aberration, scaling

of the lens means as you say scaling of the geometric spot. For the

unaberrated diffraction spot to match that you need to scale down the

sin(aperture_angle), roughly d/f, linearly. However, camera lenses have many

aberrations which are very sensitive to a change in lens diameter. For

example, SA depends of the 4th power of the distance to the optical axis,

In short, I don't understand how you derive a sqrt(f/d) rule for this.

It might be possible that you can find such a rule empirically by comparing

existing lenses, but then you can't exclude design or manufacturing changes.

For the purpose of this thread that is good enough though.

>

> So if the assumption holds, my approach is more convenient. ;-) And,

> IIRC, it holds in most situations. [I will try to remember the math

> behind this.]

Please do!

>>>Even without readout noise, assuming that it does not make sense to

>>>rasterize at resolution (e.g.) 3 times higher than the resolution of

>>>the lense, when you rescale your lense+sensor (keeping the lense

>>>design), you better rescale the pixel count and sensitivity the same

>>>amount.

BTW, there are also such devices like Electron Multiplying CCDs which tackle

that. No reason why these will not appear eventually in consumer electronics.

>

>

>>When readout noise is not a key factor it is IMO better to match the

>>pixel size to the optical bandwidth, making anti aliasing filters

>>superfluous.

>

>

> I assume that "matching" is as above: having sensor resolution "K

> times the lense resolution", for some number K? IIRC, military air

> reconnaissance photos were (Vietnam era?) scanned several times above

> the optical resolution, and it mattered. [Likewise for this 700 MP IR

> telescope?] Of course, increasing K you hit a return-of-investment

> flat part pretty soon, this is why I had chosen this low example value

> "3" above...

'Resolution' is a rather vague term, usually it is taken as Half Intensity

Width of the point spread function, or using the Rayleigh criterion. Both are

not the same as the highest spatial frequency passed by the lens,

'resolution' is for camera type optics a bit (say 50%) larger than the

highest spatial frequency. In principle it is enough to sample at twice that

frequency, so with the 50% included your 3x is reproduced!

BTW, even a bad lens with a bloated PSF produces something up to the

bandwidth, so in that case the K factor will be even higher.

>

>

>

>

> AFAIU, the current manufacturing gimmic is dSLRs. [If my analysis is

yes, a sort of horse-drawn carriage with a motor instead of the horse...

> correct] in a year or two one can have a 1'' sensor with the same

> performance as Mark II (since sensors with QE=0.8 are in production

> today, all you need is to scale the design to 12MP, and use "good"

> filter matrix). This would mean the 35mm world switching to lenses

> which are 3 times smaller, 25 times lighter, and 100 times cheaper (or

> correspondingly, MUCH MUCH better optic).

To keep sensitivity when scaling down the sensor, keeping the pixel count and

not being able to gain sensitivity, you need to keep the aperture diameter as

is, resulting in a lower f/d number, costs extra.

>

> My conjecture is that today the marketing is based on this "100 times

> cheaper" dread. The manufacturers are trying to lure the public to

> buy as many *current design* lenses as possible; they expect that

> these lenses are going to be useless in a few years, so people will

> need to change their optic again.

As 'Joe' I bought a recommended-brand P&S, assuming modern lenses for tiny

CCDs would be fine. It's not, it's abysmal. IMO such cameras and most dSLRs

are not intended to last very long. After all, see what happens to

manufacturers which make durable quality cameras (Leica, Contax), that

strategy is not working anymore.

>

> [While for professionals, who have tens K$ invested in lenses, dSLRs

> are very convenient, for Joe-the-public the EVFs of today are much

> more practical; probably producers use the first fact to confuse the

> Joes to by dSLRs too; note the stop of the development of EVF during

> the last 1/2 year, when they reached the spot they start to compete

> with dSLR, e.g., KM A200 vs A2 down-grading.]

Hm, yes, I noted also the Sony F828 is also pretty old..

>

> This is similar to DVDs today: during last several months, when

> blue-rays are at sight, studios started to digitize films as if there

> is no tomorrow...

>

> Thanks for a very interesting discussion,

Likewise, cheers, Hans

Anonymous

April 1, 2005 2:31:37 AM

[A complimentary Cc of this posting was sent to

HvdV

<nohanz@svi.nl>], who wrote in article <424C5E28.7090104@svi.nl>:

> >>>Even without readout noise, assuming that it does not make sense to

> >>>rasterize at resolution (e.g.) 3 times higher than the resolution of

> >>>the lense, when you rescale your lense+sensor (keeping the lense

> >>>design), you better rescale the pixel count and sensitivity the same

> >>>amount.

> BTW, there are also such devices like Electron Multiplying CCDs

> which tackle that. No reason why these will not appear eventually in

> consumer electronics.

I think that electron multiplying may be useful only when readout

noise is comparable with Poisson noise. When you multiply electrons,

the initial Poisson noise is not changed, but your multiplication

constant can vary (e.g., be sometimes 5, sometimes 6 - unpredictably),

an additional Poisson-like noise is added to your signal.

Additionally, the readout noise is essentially decreased the same

number of times as the multiplication constant.

Looks like it does not make sense in the photography-related settings,

since the current readout noise is low enough compared to Poisson

noise at what is jugded to be "photographically good quality" (S/N

above 20 at 18% gray).

However, note that in other thread ("Lens quality") another limiting

factor was introduced: finite capacity of sensels per area. E.g.,

current state of art of capacity per area (Canon 1D MII, 52000

electrons per 8.2mkm sensel) limits the size of 2000 electrons cell to

1.6mkm. So without technological change, there is also a restriction

of sensitivy *from below*.

Combining two estimages, this gives the low limil of cell size at

1.6mkm. However, I think that the latter restriction is only

technological, and can be overcome with more circuitry per photocell.

> 'Resolution' is a rather vague term, usually it is taken as Half

> Intensity Width of the point spread function, or using the Rayleigh

> criterion. Both are not the same as the highest spatial frequency

> passed by the lens,

Right. However, my impression is that at lens' sweet spot f-stop, all

these are closely related. At least I made calculations of MTF

functions of lenses limited by different aberrations, and all the

examples give approximately the same relations between these numbers

at the sweet spot.

> To keep sensitivity when scaling down the sensor, keeping the pixel

> count and not being able to gain sensitivity, you need to keep the

> aperture diameter as is, resulting in a lower f/d number, costs

> extra.

What happens is you keep the aperture diameter the same, and want to

keep the field of view the same, but the focal length smaller. This

"obviously" can't be done without addition additional elements.

However, these "additions" may happen on the "sensor" side of the

lens, not on the subject side. So the added elements are actually

small in diameter (since sensor is so much smaller), so much cheaper

to produce. This will not add a lot to the lens price.

Hmm, maybe this may work... The lengths of optical paths through the

"old" part of the lens will preserve their mismatches; if added

elements somewhat compensate these mismatches, it will have much

higher optical quality, and price not much higher than the original.

> As 'Joe' I bought a recommended-brand P&S, assuming modern lenses for tiny

> CCDs would be fine. It's not, it's abysmal. IMO such cameras and most dSLRs

> are not intended to last very long. After all, see what happens to

> manufacturers which make durable quality cameras (Leica, Contax), that

> strategy is not working anymore.

Right. After 3 newer-generation VCRs almost immediately broke down, I

went to my garage, fetched a 15-years old VCR, and use it happily ever

after. :-(

Yours,

Ilya

Anonymous

April 1, 2005 3:54:14 PM

In article <d2hsb1$27me$1@agate.berkeley.edu>, Ilya Zakharevich

<nospam-abuse@ilyaz.org> writes

>

>However, note that in other thread ("Lens quality") another limiting

>factor was introduced: finite capacity of sensels per area. E.g.,

>current state of art of capacity per area (Canon 1D MII, 52000

>electrons per 8.2mkm sensel) limits the size of 2000 electrons cell to

>1.6mkm. So without technological change, there is also a restriction

>of sensitivy *from below*.

>

"mkm"? Not a recognised unit; could you please clarify.

David

--

David Littlewood

Anonymous

April 1, 2005 5:42:00 PM

David Littlewood wrote:

[]

> "mkm"? Not a recognised unit; could you please clarify.

>

> David

He says it's micrometres but he refuses to use "um".

David

Anonymous

April 1, 2005 7:32:31 PM

In article <Icc3e.1580$G8.828@text.news.blueyonder.co.uk>, David J

Taylor <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> writes

>David Littlewood wrote:

>[]

>> "mkm"? Not a recognised unit; could you please clarify.

>>

>> David

>

>He says it's micrometres but he refuses to use "um".

>

>David

>

>

Ah! Bernard's irregular verb from "Yes Minister" springs to mind.

Thanks.

David

--

David Littlewood

Anonymous

April 1, 2005 7:32:32 PM

David Littlewood wrote:

> In article <Icc3e.1580$G8.828@text.news.blueyonder.co.uk>, David J

> Taylor <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk>

> writes

>> David Littlewood wrote:

>> []

>>> "mkm"? Not a recognised unit; could you please clarify.

>>>

>>> David

>>

>> He says it's micrometres but he refuses to use "um".

>>

>> David

>>

>>

> Ah! Bernard's irregular verb from "Yes Minister" springs to mind.

>

> Thanks.

>

> David

Unfortunately it doesn't improve the credibility of anything else he says.

I presume we're in for a few weeks of "Yes, Minister" speak ourselves over

the next few weeks!

Cheers,

David

Anonymous

April 6, 2005 2:43:45 AM

Hi Ilya,

>

>

>>BTW, there are also such devices like Electron Multiplying CCDs

>>which tackle that. No reason why these will not appear eventually in

>>consumer electronics.

>

>

(snip)

>

>

> However, note that in other thread ("Lens quality") another limiting

> factor was introduced: finite capacity of sensels per area. E.g.,

> current state of art of capacity per area (Canon 1D MII, 52000

> electrons per 8.2mkm sensel) limits the size of 2000 electrons cell to

> 1.6mkm. So without technological change, there is also a restriction

> of sensitivy *from below*.

One advantage of the EMCCDs is there speed: up to 100fps. One could use that

speed for example for smart averaging including motion compensation, depth of

focus manipulation in combination with moving the focus, have stop here

before getting carried away....

>

> Combining two estimages, this gives the low limil of cell size at

> 1.6mkm. However, I think that the latter restriction is only

> technological, and can be overcome with more circuitry per photocell.

ok

>

>

>>'Resolution' is a rather vague term, usually it is taken as Half

>>Intensity Width of the point spread function, or using the Rayleigh

>>criterion. Both are not the same as the highest spatial frequency

>>passed by the lens,

>

>

> Right. However, my impression is that at lens' sweet spot f-stop, all

> these are closely related. At least I made calculations of MTF

> functions of lenses limited by different aberrations, and all the

> examples give approximately the same relations between these numbers

> at the sweet spot.

The theoretical bandlimit is not affected by the aberrations, but the 50% MTF

point of course strongly.

>

>

>>To keep sensitivity when scaling down the sensor, keeping the pixel

>>count and not being able to gain sensitivity, you need to keep the

>>aperture diameter as is, resulting in a lower f/d number, costs

>>extra.

>

>

> What happens is you keep the aperture diameter the same, and want to

> keep the field of view the same, but the focal length smaller. This

> "obviously" can't be done without addition additional elements.

yes

> However, these "additions" may happen on the "sensor" side of the

> lens, not on the subject side. So the added elements are actually

> small in diameter (since sensor is so much smaller), so much cheaper

> to produce. This will not add a lot to the lens price.

Looking at prices for microscope lenses I'm not so sure :-)

>

> Hmm, maybe this may work... The lengths of optical paths through the

> "old" part of the lens will preserve their mismatches; if added

> elements somewhat compensate these mismatches, it will have much

> higher optical quality, and price not much higher than the original.

I don't know much about lens designing, but I think that as soon as you add a

single element, make one aspherical surface or use some glass with special

dispersion properties you have to redo the entire optimization process. That

might be not so hard provided the basic design ideas are good, but probably

it is much pricier to manufacture the whole scaled up design to sufficient

accuracy.

Cheers, hans

Anonymous

April 6, 2005 2:50:01 AM

Alfred Molon wrote:

> In article <d1spvr$2qj8$1@agate.berkeley.edu>, Ilya Zakharevich says...

>

>

>>Are there actual back-illumination sensor used in mass-production

>>digicams?

>

>

> To my knowledge no - they are all used for astronomy. The production

Good camera's for fluorescence microscopy use them too. I guess the

efficiency gain is not sufficient to justify the current price difference (>>

$1) for use in digicams.

-- hans

Anonymous

April 9, 2005 12:06:27 PM

[A complimentary Cc of this posting was sent to

HvdV

<nohanz@svi.nl>], who wrote in article <4252F881.5020808@svi.nl>:

> > However, note that in other thread ("Lens quality") another limiting

> > factor was introduced: finite capacity of sensels per area. E.g.,

> > current state of art of capacity per area (Canon 1D MII, 52000

> > electrons per 8.2mkm sensel) limits the size of 2000 electrons cell to

> > 1.6mkm. So without technological change, there is also a restriction

> > of sensitivy *from below*.

> One advantage of the EMCCDs is there speed: up to 100fps. One could

> use that speed for example for smart averaging including motion

> compensation, depth of focus manipulation in combination with moving

> the focus, have stop here before getting carried away....

To do this, you need low readout noise. The data for Canon 1D MII

(readout noise about 12 electrons) prohibits making more than about 4

"subexposition" per exposition (without significant reduction of

noise).

> >>'Resolution' is a rather vague term, usually it is taken as Half

> >>Intensity Width of the point spread function, or using the Rayleigh

> >>criterion. Both are not the same as the highest spatial frequency

> >>passed by the lens,

> > Right. However, my impression is that at lens' sweet spot f-stop, all

> > these are closely related. At least I made calculations of MTF

> > functions of lenses limited by different aberrations, and all the

> > examples give approximately the same relations between these numbers

> > at the sweet spot.

> The theoretical bandlimit is not affected by the aberrations, but

> the 50% MTF point of course strongly.

My point was with all kinds of individual aberrations I checked, at

the sweet spot the 20% MTF point WITH aberrations was approximately at

the same percentage of the cutoff frequency (given by diffration).

From this it follows that particular "numeric" performance at the

sweet-spot should be quite predictable.

Of course, the quality of the lens image cannot be described by one

number; so when the lens is at sweet spot for one parameter (e.g.,

radial MTF at 1/4 of diagonal size from center), it is far from sweet

spot for other parameters. On the other hand, on a well-optimized

lens a lot of parameters have sweet spots at the same aperture.

[This follows from an assumption that improving one parameter will

negatively affect others; so with multi-argument optimization a lot

of parameters reach their margin values simultaneously.]

> > However, these "additions" may happen on the "sensor" side of the

> > lens, not on the subject side. So the added elements are actually

> > small in diameter (since sensor is so much smaller), so much cheaper

> > to produce. This will not add a lot to the lens price.

> Looking at prices for microscope lenses I'm not so sure :-)

This particular market can bear?

> > Hmm, maybe this may work... The lengths of optical paths through the

> > "old" part of the lens will preserve their mismatches; if added

> > elements somewhat compensate these mismatches, it will have much

> > higher optical quality, and price not much higher than the original.

> I don't know much about lens designing, but I think that as soon as

> you add a single element, make one aspherical surface or use some

> glass with special dispersion properties you have to redo the entire

> optimization process. That might be not so hard provided the basic

> design ideas are good, but probably it is much pricier to

> manufacture the whole scaled up design to sufficient accuracy.

Given an overall design (which stuff goes into which groups, etc), and

given clear goal functions, I would expect the optimization process

should be more or less trivial. So it follows that it is the

design/goals part which must require some skill... ;-)

Yours,

Ilya

Anonymous

May 6, 2005 1:45:32 PM

Dave Martindale <davem@cs.ubc.ca> wrote:

> andrew29@littlepinkcloud.invalid writes:

>>[1] The Reproduction of Colour, 6th Edition, Robert Hunt, p556.

> I didn't realize that the 6th edition was out. Does it say how it

> differs from the previous edition (e.g. in a preface?).

> I do have the 3rd, 4th, and 5th editions already, but they don't cover

> digital imaging much.

Sorry I didn't reply before now. The difference in the 6th. ed. is

indeed coverage of digital imaging.

Andrew.

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