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Magnification using a Digital SLR

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Anonymous
May 22, 2005 12:17:40 PM

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

Does the 1.6 factor affect the maximum magnification of a lens
compared to a film SLR?
Anonymous
May 22, 2005 12:17:41 PM

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

Phil M <none@none.net> writes:
> Does the 1.6 factor affect the maximum magnification of a lens
> compared to a film SLR?

In terms of image size on the sensor, no, but that's not terribly
meaningful. In terms of how close you can focus, not at all. In
terms of how small an image will fill the frame at the closest focus,
yes, 1.6x smaller.
Anonymous
May 22, 2005 12:17:41 PM

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

"Phil M" <none@none.net> wrote in message
news:cvf091lmuoai4v7n37ba0q3qk9o42tn79c@4ax.com...
> Does the 1.6 factor affect the maximum magnification of a lens
> compared to a film SLR?

http://www.lookbefore.wading-in.net/lookbefore/Digital_...

Should help clarify it for you.

Jim Kramer
Related resources
Anonymous
May 22, 2005 1:41:44 PM

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

Phil M <none@none.net> wrote:
: Does the 1.6 factor affect the maximum magnification of a lens
: compared to a film SLR?

Yes, kinda. :) 

In focus, depth of field, f-stop, exposure no. But with respect to
effective length of a lens, yes. The lens works the same but due to the
difference between a 35mm film frame and a digital sensor dimensions, the
effective length of the lens (mm) will be increased by 1.6x. So if you
took a photo with the digital camera and a 100mm lens, you would end up
with an image that would be roughly equal to the same photo taken with a
35mm camera with a 160mm lens. This assumes the camera does have a 1.6x
conversion (not all brands do). This multiplier continues all across the
lens spectrum so an 18mm lens on this digital camera would be the 35mm
equivalent of a 28.8mm lens. So the multiplier hurts wide angle lenses. On
the other end a 300mm lens on the digital would give you images equivalent
to a 480mm lens on a film camera. So the conversion will greatly help your
telephoto lenses. But I want to reemphasize that other than lens length,
all other functions remain the same.

Randy

==========
Randy Berbaum
Champaign, IL
Anonymous
May 22, 2005 1:41:45 PM

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

Randy Berbaum wrote:

> Phil M <none@none.net> wrote:
> : Does the 1.6 factor affect the maximum magnification of a lens
> : compared to a film SLR?
>
> Yes, kinda. :) 
>
> In focus, depth of field, f-stop, exposure no. But with respect to
> effective length of a lens, yes. The lens works the same but due to the
> difference between a 35mm film frame and a digital sensor dimensions, the
> effective length of the lens (mm) will be increased by 1.6x. So if you
> took a photo with the digital camera and a 100mm lens, you would end up
> with an image that would be roughly equal to the same photo taken with a
> 35mm camera with a 160mm lens.

No. I can crop my 35mm film image the same amount, and enlarge
it the same amount as the digital image. It is a crop factor.
The only way there is equivalence is in field of view.
With the digital crop factor, the field of view is smaller.
If you want the illusion of longer focal length then just
crop 35 35mm film images too.

Roger
Anonymous
May 22, 2005 2:47:55 PM

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

On 22 May 2005 06:35:51 EDT, "jimkramer"
<Sophomoric1_jim@NOSPAMjlkramer.net> wrote:

>"Phil M" <none@none.net> wrote in message
>news:cvf091lmuoai4v7n37ba0q3qk9o42tn79c@4ax.com...
>> Does the 1.6 factor affect the maximum magnification of a lens
>> compared to a film SLR?
>
>http://www.lookbefore.wading-in.net/lookbefore/Digital_...
>
>Should help clarify it for you.
>
>Jim Kramer
>
Thanks all :) 
Anonymous
May 22, 2005 6:26:57 PM

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

"Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote in
message news:42907BB2.9000009@qwest.net...
> Randy Berbaum wrote:
>
>> Phil M <none@none.net> wrote:
>> : Does the 1.6 factor affect the maximum magnification of a lens
>> : compared to a film SLR? Yes, kinda. :) 
>>
>> In focus, depth of field, f-stop, exposure no. But with respect to
>> effective length of a lens, yes. The lens works the same but due to the
>> difference between a 35mm film frame and a digital sensor dimensions, the
>> effective length of the lens (mm) will be increased by 1.6x. So if you
>> took a photo with the digital camera and a 100mm lens, you would end up
>> with an image that would be roughly equal to the same photo taken with a
>> 35mm camera with a 160mm lens.
>
> No. I can crop my 35mm film image the same amount, and enlarge
> it the same amount as the digital image. It is a crop factor.

No, it isn't a "crop factor" and it sure would be nice if people would stop
using that silly term.

Digital camera focal lengths are commonly given in terms of 35mm
equivalence. There is nothing unreasonable or complicated about that. Most
of us are used to thinking of field of view in 35mm f.l. terms, which is the
only reason for this. So the 1.6x factor (i.e., the consequence of the
effective diagonal of the digital camera's sensor being 1/1.6 the diagonal
of a full 35mm frame) is effectively a focal length multiplier as far as
35mm equivalence is concerned: a 50mm lens becomes *effectively* an 80mm
lens in that sense, and so on.

Nothing is cropped; there is no "crop factor." The fact that the digital
camera's APS format is smaller than that of a 35 doesn't make it "cropped"
any more than a 35mm frame is "cropped" because it's smaller than that of a
120 negative.


> The only way there is equivalence is in field of view.

That's exactly what the factor refers to in terms of lens focal length.
Ergo, it's a multiplier. It has no other meaning.


> With the digital crop factor, the field of view is smaller.

There isn't any "digital crop factor." The term is nonsensical. You can't
possibly crop 1.6x of anything anyway. If you crop 0.5x of an image it's
half gone. If you crop 1x of it it's *all* gone and there's nothing left to
crop.

N.
Anonymous
May 22, 2005 10:35:36 PM

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

Nostrobino wrote:

> "Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote in
> message news:42907BB2.9000009@qwest.net...
>
>>Randy Berbaum wrote:
>>
>>
>>>Phil M <none@none.net> wrote:
>>>: Does the 1.6 factor affect the maximum magnification of a lens
>>>: compared to a film SLR? Yes, kinda. :) 
>>>
>>>In focus, depth of field, f-stop, exposure no. But with respect to
>>>effective length of a lens, yes. The lens works the same but due to the
>>>difference between a 35mm film frame and a digital sensor dimensions, the
>>>effective length of the lens (mm) will be increased by 1.6x. So if you
>>>took a photo with the digital camera and a 100mm lens, you would end up
>>>with an image that would be roughly equal to the same photo taken with a
>>>35mm camera with a 160mm lens.
>>
>>No. I can crop my 35mm film image the same amount, and enlarge
>>it the same amount as the digital image. It is a crop factor.
>
>
> No, it isn't a "crop factor" and it sure would be nice if people would stop
> using that silly term.

Yes, it is a crop factor. The smaller sensor is doing the cropping.
Note Phil said:
>> So if you
>>>took a photo with the digital camera and a 100mm lens, you would end up
>>>with an image that would be roughly equal to the same photo taken with a
>>>35mm camera with a 160mm lens.

If I took an image on 35mm with a 160mm lens compared it to
a 100mm lens on a DSLR (6 to 8 MPix), the only common
thing in the image would be field of view. The 35mm film
image with 160mm focal length would show a lot more detail.
Just like a longer focal length on medium format would
give images with more detail but the same field of view.
It is incorrect to imply that the smaller sensor size
of digital cameras magnify the focal length of telephoto
lenses. 100mm is 100 mm. The sensor is just the field
of view.

Roger
Anonymous
May 23, 2005 1:37:13 AM

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

"Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote in
message news:42912558.6010101@qwest.net...
> Nostrobino wrote:
>
>> "Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote
>> in message news:42907BB2.9000009@qwest.net...
>>
>>>Randy Berbaum wrote:
>>>
>>>
>>>>Phil M <none@none.net> wrote:
>>>>: Does the 1.6 factor affect the maximum magnification of a lens
>>>>: compared to a film SLR? Yes, kinda. :) 
>>>>
>>>>In focus, depth of field, f-stop, exposure no. But with respect to
>>>>effective length of a lens, yes. The lens works the same but due to the
>>>>difference between a 35mm film frame and a digital sensor dimensions,
>>>>the effective length of the lens (mm) will be increased by 1.6x. So if
>>>>you took a photo with the digital camera and a 100mm lens, you would end
>>>>up with an image that would be roughly equal to the same photo taken
>>>>with a 35mm camera with a 160mm lens.
>>>
>>>No. I can crop my 35mm film image the same amount, and enlarge
>>>it the same amount as the digital image. It is a crop factor.
>>
>>
>> No, it isn't a "crop factor" and it sure would be nice if people would
>> stop using that silly term.
>
> Yes, it is a crop factor. The smaller sensor is doing the cropping.

There is no cropping being done, Roger. None.

As I pointed out, you might just as well say a 35mm camera is cropping the
image because its frame is smaller than a 120 camera. Then of course you
could say the 120 camera is cropping because its film size is smaller than a
4 x 5 view camera. And so on. This simply makes the term "cropping"
absolutely meaningless and silly.


> Note Phil said:
> >> So if you
> >>>took a photo with the digital camera and a 100mm lens, you would end up
> >>>with an image that would be roughly equal to the same photo taken with
> >>>a
> >>>35mm camera with a 160mm lens.
>
> If I took an image on 35mm with a 160mm lens compared it to
> a 100mm lens on a DSLR (6 to 8 MPix), the only common
> thing in the image would be field of view.

That's all that's necessary. People want to relate to field of view in 35mm
terms, because otherwise focal length numbers in a digital camera are
relatively meaningless. That is *why* 35mm equivalents are used so much. If
a digital camera has a 3x zoom lens of 7.8 to 23.4 mm, who knows what that
means? It's just meaningless numbers to the average camera user. If you know
that *in that particular camera* it means the equivalent of a 35-105mm zoom,
*then* you have useful information.


> The 35mm film
> image with 160mm focal length would show a lot more detail.

Not necessarily, and anyway that's not the chief reason for wanting to know
the focal length--or its equivalent. We change focal length to change field
of view, as well as those things directly related to field of view of
course.


> Just like a longer focal length on medium format would
> give images with more detail but the same field of view.
> It is incorrect to imply that the smaller sensor size
> of digital cameras magnify the focal length of telephoto
> lenses. 100mm is 100 mm. The sensor is just the field
> of view.
>
> Roger

Roger, "just the field of view" is the ONLY thing the multiplier refers to.
Obviously the actual focal length doesn't change. Why do you suppose anyone
wants to know what the multiplier is in the first place?

If I need something with, say, the coverage of a 28mm lens (on a 35), that's
the important thing to me. I don't need to know (or particularly care) what
the actual focal length is.

N.
Anonymous
May 23, 2005 1:37:14 AM

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

Nostrobino wrote:

> Roger, "just the field of view" is the ONLY thing the multiplier refers to.
> Obviously the actual focal length doesn't change. Why do you suppose anyone
> wants to know what the multiplier is in the first place?

I agree that the multiplier refers to field of view.
But calling it a multiplier is what causes the confusion. It is
spread throughout this thread. Examples (doesn't matter who said it;
the fact that it is said shows the term multiplier causes confusion):

>>>>>: Does the 1.6 factor affect the maximum magnification of a lens
>>>>>: compared to a film SLR? Yes, kinda.

>>>>>So if
>>>>>you took a photo with the digital camera and a 100mm lens, you would end
>>>>>up with an image that would be roughly equal to the same photo taken
>>>>>with a 35mm camera with a 160mm lens.

> The lens works the same but due to the
> difference between a 35mm film frame and a digital sensor dimensions, the
> effective length of the lens (mm) will be increased by 1.6x.

A google search will turn up many more confusing statements. People
constantly say how the 1.6 factor gives them more magnification
on the telephoto end.

Perhaps multiplier should be dropped and field of view equivalent
should be used, and perhaps field of view factor.

> If I need something with, say, the coverage of a 28mm lens (on a 35), that's
> the important thing to me. I don't need to know (or particularly care) what
> the actual focal length is.

But if you have a 35mm film camera and a DSLR with a 1.6 "factor,"
the DSLR is cropping the focal plane of the lens. So crop factor
is more appropriate than multiplier.

Roger
Anonymous
May 23, 2005 1:37:14 AM

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

Crop factor is relevant in as much as it specifies the actual light
hitting the sensor/film. It's confusing because one sensor might be more
capable than another but if you put the same sensor in another camera or
behind another lens, the "less crop factor" setup would have more potential.

If you figure the ability of the sensor to print up to a certain size
and a lens good enough to use it's capabilities then the "max print
size" for the sensor would be more relevant than the crop factor.
Anonymous
May 23, 2005 2:11:16 PM

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

"Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote in
message news:42913E65.9030206@qwest.net...
> Nostrobino wrote:
>
>> Roger, "just the field of view" is the ONLY thing the multiplier refers
>> to. Obviously the actual focal length doesn't change. Why do you suppose
>> anyone wants to know what the multiplier is in the first place?
>
> I agree that the multiplier refers to field of view.
> But calling it a multiplier is what causes the confusion. It is

No, multiplier is what it *is*. If it weren't a multiplier, then what would
be the function of the 1.6 (or whatever) number at all? The fact that it's
commonly written 1.6x shows that it's a multiplier, and that is exactly how
it's used.

Example: I have a large number of Minolta Maxxum lenses. One of them is 17mm
at the short end, which of course is ultrawide. But how wide an angle would
it cover on a Maxxum 7D, i.e. what familiar 35mm focal length would that
equate to? The *only* way I can know this is to know the multiplier, which
is about 1.5x in the case of this camera. So now I know the lens at shortest
f.l. would be equivalent to about 25mm in familiar 35 terms. That's useful
information, and I need the multiplier to get it.

In many digital cameras the multiplier is already factored in. For example,
my Minolta 7Hi has a manual zoom lens on which the f.l. markings on the zoom
ring range from 28mm to 200mm. Those are not the *actual* focal lengths or
anywhere near them. It doesn't matter. I have what is effectively a 28-200mm
lens (in familiar 35 terms), which is all I need to know.


> spread throughout this thread. Examples (doesn't matter who said it;
> the fact that it is said shows the term multiplier causes confusion):
>
> >>>>>: Does the 1.6 factor affect the maximum magnification of a lens
> >>>>>: compared to a film SLR? Yes, kinda.
>
> >>>>>So if
> >>>>>you took a photo with the digital camera and a 100mm lens, you would
> >>>>>end
> >>>>>up with an image that would be roughly equal to the same photo taken
> >>>>>with a 35mm camera with a 160mm lens.
>
> > The lens works the same but due to the
> > difference between a 35mm film frame and a digital sensor dimensions,
> > the
> > effective length of the lens (mm) will be increased by 1.6x.
>
> A google search will turn up many more confusing statements. People
> constantly say how the 1.6 factor gives them more magnification
> on the telephoto end.

But that isn't "confusing," Roger. It's *correct*. If you have a digital SLR
with a 1.6x multiplier as in your examples, using a 300mm lens on it gives
an effective f.l. of 480mm. That *is* more magnification than the same lens
provided on a 35mm camera.


>
> Perhaps multiplier should be dropped and field of view equivalent
> should be used,

But that's *exactly* what the multiplier does! The field of view is
expressed in terms of familiar 35mm focal lengths. The alternative would be
what, to express it in degrees? Who ever does that? Have you ever in your
entire life heard anyone refer to a 28mm lens as a 75-degree lens?


> and perhaps field of view factor.

<groan>
"field of view factor"?!


>
>> If I need something with, say, the coverage of a 28mm lens (on a 35),
>> that's the important thing to me. I don't need to know (or particularly
>> care) what the actual focal length is.
>
> But if you have a 35mm film camera and a DSLR with a 1.6 "factor,"
> the DSLR is cropping the focal plane of the lens.

No, it is not. Cropping means cutting away or discarding some part of the
recorded image--for example, using less than the full image on a negative or
slide. Anything *not* on the film cannot possibly be cropped. The same
applies to any CCD or other digital sensor. If it's not part of the image
*on the sensor* it can't possibly be cropped.

I understand what you're saying: that the digital sensor isn't capturing all
of the image produced by the lens at the focal plane. That is true. But it's
*always* true. A camera lens produces an image circle. With very few
exceptions (such as certain fisheye lenses), a camera does not record the
entire image circle on its film or other medium. So does that mean that
every camera producing a rectangular final image must be "cropping"? Of
course not.

Anyway, many of the lenses now made specifically for digital SLRs do *not*
cover the full 35mm frame, even if they can be used on 35s. They cover only
what they have to cover, i.e. the size of the sensor used. See what that
does to the "crop factor" idea? But the user *still* needs to know the
multiplier if he wants to relate to familiar 35mm focal lengths.

By the way, consider the view camera. It is usually fitted with a lens
having much more coverage than the film format, to allow for perspective
control by swings, tilts and shifts. Would you say a view camera is
"cropping" because it uses only a portion of the image available at its
focal plane? Of course not.

The same thing applies (to a lesser degree) to perspective-control lenses
for 35mm cameras. Is a 35mm tilt-and-shift lens on a 35 "cropping" because
the camera uses only part of its image circle (though it still fills the
frame of course), while a conventional 35mm lens on the same camera would
not be cropping? Of course not.

Cropping, as the term has always been used in photographic circles (no pun
intended), is something done to the recorded image. It has no possible
bearing on anything not recorded, at least in general usage.

N.
Anonymous
May 23, 2005 2:13:38 PM

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

Please see the reply I just left for Roger.

N.


"Paul Furman" <paul-@-edgehill.net> wrote in message
news:zbqdnZBlVvn81AzfRVn-2A@speakeasy.net...
> Crop factor is relevant in as much as it specifies the actual light
> hitting the sensor/film. It's confusing because one sensor might be more
> capable than another but if you put the same sensor in another camera or
> behind another lens, the "less crop factor" setup would have more
> potential.
>
> If you figure the ability of the sensor to print up to a certain size and
> a lens good enough to use it's capabilities then the "max print size" for
> the sensor would be more relevant than the crop factor.
Anonymous
May 24, 2005 2:32:33 AM

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

Nostrobino wrote:

> No, multiplier is what it *is*. If it weren't a multiplier, then what would
> be the function of the 1.6 (or whatever) number at all? The fact that it's
> commonly written 1.6x shows that it's a multiplier, and that is exactly how
> it's used.

It is a crop factor. It is a multiplier. It is a magnifier. It is all three.
But it doesn't magnify focal length. The magnification factor is how
much more you have to magnify the image from the focal plane to get
a certain size enlargement compared to 35mm. It is a multiplier
(really a divisor) that decreases the field of view. You can accomplish
the EXACT same effects by cropping a 35mm film image, or a full frame
DSLR image and magnifying it more (ignoring resolution differences
between sensor/film).

> In many digital cameras the multiplier is already factored in. For example,
> my Minolta 7Hi has a manual zoom lens on which the f.l. markings on the zoom
> ring range from 28mm to 200mm. Those are not the *actual* focal lengths or
> anywhere near them. It doesn't matter. I have what is effectively a 28-200mm
> lens (in familiar 35 terms), which is all I need to know.

But you are being fooled, because the performance is different if not
really that focal length. Example, 200mm f/4: if it is really 50mm f/4,
then the clear aperture is 4 times smaller than reality. If you were
doing astrophotography, you wouldn't record as faint of stars as would
be indicated by the stated (incorrect) focal length. Similarly, the
resolution of distant objects would be quite different between true
focal lengths of the 4x different focal lengths. The only equivalence
is field of view. Everything else, from resolution to clear aperture,
to size of an object in the focal plane is a lie.

> But that isn't "confusing," Roger. It's *correct*. If you have a digital SLR
> with a 1.6x multiplier as in your examples, using a 300mm lens on it gives
> an effective f.l. of 480mm. That *is* more magnification than the same lens
> provided on a 35mm camera.

This proves that your are confused too, Focal length has not changed.
What the 1.6 factor means is that the image in the focal plane must
be magnified in a print (or on screen) 1.6 times more to make a given
size print. Example: full frame DSLR = 0.94 inches by 1.4 inches with
a 100mm lens. Let's do a 10x enlargement: 9.4 x 14 inches.
Now put a 50mm lens on the 2x multiplier sensor: sensor
size = 0.47 x 0.7 inches. To make the same print of 9.4 x 14 inches
covering the same field of view with objects in the print the same
size, one needs to magnify the image from the focal plane by 20x.
See, the multiplier factor is the magnification to make the same
size print relative to the full frame sensor.

This is no different than if we took the full frame DSLR, put a 50mm
lens on the camera, took the picture, cropped it 50% and enlarged
that center portion 20x.

In neither case did the 50mm lens become a 100mm lens. Do you
see this?


> No, it is not. Cropping means cutting away or discarding some part of the
> recorded image--for example, using less than the full image on a negative or
> slide. Anything *not* on the film cannot possibly be cropped. The same
> applies to any CCD or other digital sensor. If it's not part of the image
> *on the sensor* it can't possibly be cropped.

It was cropped by the manufacturer when they designed the smaller than
35mm sensor.

> I understand what you're saying: that the digital sensor isn't capturing all
> of the image produced by the lens at the focal plane. That is true. But it's
> *always* true. A camera lens produces an image circle. With very few
> exceptions (such as certain fisheye lenses), a camera does not record the
> entire image circle on its film or other medium. So does that mean that
> every camera producing a rectangular final image must be "cropping"? Of
> course not.

You are mixing image circle with 35mm equivalent size. If 35mm is the
standard size, then other sensors smaller than that "standard size" are
simply cropped versions. You cite the 35mm system as the reference,
then abandon it when it doesn't suit your argument.
>
> Anyway,
.... snipped because the discussion abandoned the 35mm reference.

Roger
Anonymous
May 24, 2005 2:12:11 PM

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

"Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote in
message news:4292AE61.5070804@qwest.net...
> Nostrobino wrote:
>
>> No, multiplier is what it *is*. If it weren't a multiplier, then what
>> would be the function of the 1.6 (or whatever) number at all? The fact
>> that it's commonly written 1.6x shows that it's a multiplier, and that is
>> exactly how it's used.
>
> It is a crop factor. It is a multiplier. It is a magnifier. It is all
> three.

Well, two out of three ain't bad.

Explain how it is a "crop factor," please. In other words, just tell me
exactly how the number 1.6 relates to, or is used in determining, a crop. I
know how it relates to focal length, which (as I have been saying) is its
*only* application. So don't tell me anything about focal length. Just
explain what it is you do with the number 1.6 that has to do directly with
cropping.


> But it doesn't magnify focal length.

Roger, no one thinks it magnifies *actual* focal length. There is no
disagreement there, and that's irrelevant.


> The magnification factor is how
> much more you have to magnify the image from the focal plane to get
> a certain size enlargement compared to 35mm. It is a multiplier
> (really a divisor) that decreases the field of view.

No, it's not a divisor, at least not in any useful way. Yes, of course it
decreases the field of view.


> You can accomplish
> the EXACT same effects by cropping a 35mm film image, or a full frame
> DSLR image and magnifying it more (ignoring resolution differences
> between sensor/film).

Sure. No one has said, suggested, implied or hinted otherwise.


>
>> In many digital cameras the multiplier is already factored in. For
>> example, my Minolta 7Hi has a manual zoom lens on which the f.l. markings
>> on the zoom ring range from 28mm to 200mm. Those are not the *actual*
>> focal lengths or anywhere near them. It doesn't matter. I have what is
>> effectively a 28-200mm lens (in familiar 35 terms), which is all I need
>> to know.
>
> But you are being fooled, because the performance is different if not
> really that focal length. Example, 200mm f/4: if it is really 50mm f/4,
> then the clear aperture is 4 times smaller than reality. If you were
> doing astrophotography, you wouldn't record as faint of stars as would
> be indicated by the stated (incorrect) focal length.

Astrophotography is different. It depends on physical aperture size (for
recording faint stars) rather than f-number. That really has no bearing on
earthly photography, which is all I'm doing. I don't even know anyone who
does astrophotography. I don't think I even know anyone who *knows* anyone
who does astrophotography.


> Similarly, the
> resolution of distant objects would be quite different between true
> focal lengths of the 4x different focal lengths. The only equivalence
> is field of view. Everything else, from resolution to clear aperture,
> to size of an object in the focal plane is a lie.

Field of view is what matters. It's the primary (if not only) reason for
choosing a focal length. If anyone wants to know what the actual f.l. is,
that's engraved on the lens bezel, but really, who cares? What I want to
know is the f.l. in terms of 35mm equivalence. That's a standard that people
recognize. What does an actual f.l. number like 8.4mm tell you? Unless all
digital cameras have the same size sensor (which is not going to happen in
my lifetime), such a number is meaningless as far as the typical user is
concerned.

I'm *sure* you can't really be having so much difficulty understanding this,
Roger.


>
>> But that isn't "confusing," Roger. It's *correct*. If you have a digital
>> SLR with a 1.6x multiplier as in your examples, using a 300mm lens on it
>> gives an effective f.l. of 480mm. That *is* more magnification than the
>> same lens provided on a 35mm camera.
>
> This proves that your are confused too, Focal length has not changed.

Actual f.l. has not changed. Correct. We don't have to keep addressing this
same point over and over.


> What the 1.6 factor means is that the image in the focal plane must
> be magnified in a print (or on screen) 1.6 times more to make a given
> size print.

Yes. So it's multiplier, not a "crop factor." You can say the same thing
about *any* two formats that are different in size. A 35mm negative has to
be enlarged about 8x to make an 8 x 10 print, whereas a 4 x 5 negative only
has to be enlarged 2x. So does that mean a 35mm camera has a "crop factor"
of 4?


> Example: full frame DSLR = 0.94 inches by 1.4 inches with
> a 100mm lens. Let's do a 10x enlargement: 9.4 x 14 inches.
> Now put a 50mm lens on the 2x multiplier sensor: sensor
> size = 0.47 x 0.7 inches. To make the same print of 9.4 x 14 inches
> covering the same field of view with objects in the print the same
> size, one needs to magnify the image from the focal plane by 20x.
> See, the multiplier factor is the magnification to make the same
> size print relative to the full frame sensor.
>
> This is no different than if we took the full frame DSLR, put a 50mm
> lens on the camera, took the picture, cropped it 50% and enlarged
> that center portion 20x.
>
> In neither case did the 50mm lens become a 100mm lens. Do you
> see this?

Roger, we don't have to keep going over this same ground again and again. No
one says a lens *becomes* a different f.l. when used on a digital SLR.


>
>
>> No, it is not. Cropping means cutting away or discarding some part of the
>> recorded image--for example, using less than the full image on a negative
>> or slide. Anything *not* on the film cannot possibly be cropped. The same
>> applies to any CCD or other digital sensor. If it's not part of the image
>> *on the sensor* it can't possibly be cropped.
>
> It was cropped by the manufacturer when they designed the smaller than
> 35mm sensor.

What we have here is a problem in semantics. I'm saying you can't *crop*
part of an image that never was recorded in the first place. You're using
"crop" to mean something it has never meant in general photography, as far
as I am aware.


>
>> I understand what you're saying: that the digital sensor isn't capturing
>> all of the image produced by the lens at the focal plane. That is true.
>> But it's *always* true. A camera lens produces an image circle. With very
>> few exceptions (such as certain fisheye lenses), a camera does not record
>> the entire image circle on its film or other medium. So does that mean
>> that every camera producing a rectangular final image must be "cropping"?
>> Of course not.
>
> You are mixing image circle with 35mm equivalent size. If 35mm is the
> standard size, then other sensors smaller than that "standard size" are
> simply cropped versions.

Smaller, not "cropped."


> You cite the 35mm system as the reference,
> then abandon it when it doesn't suit your argument.

I "cite the 35mm system as the reference" only in terms of focal length
equivalences. This is legitimate because such equivalences have clear
meaning for anyone who's been in photography for a while. That's why digital
camera manufacturers do it, camera reviewers do it, and photography
publications do it.

Nor is this something new with digital cameras. The same thing was done when
APS cameras came out; the multiplier in that case was 1.25 and publications
commonly used this, giving the actual f.l. of the camera lens and *also* the
35mm equivalent. For example, a magazine article describing an APS camera
with a 28-56mm lens would also mention that that was 35-70mm in 35mm
equivalence.

It's the standard and well-established practice, Roger.

N.
Anonymous
May 25, 2005 2:44:53 AM

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

Nostrobino wrote:
> "Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote in
> message news:4292AE61.5070804@qwest.net...
>
>>You cite the 35mm system as the reference,
>>then abandon it when it doesn't suit your argument.
>
>
> I "cite the 35mm system as the reference" only in terms of focal length
> equivalences. This is legitimate because such equivalences have clear
> meaning for anyone who's been in photography for a while. That's why digital
> camera manufacturers do it, camera reviewers do it, and photography
> publications do it.
>
> Nor is this something new with digital cameras. The same thing was done when
> APS cameras came out; the multiplier in that case was 1.25 and publications
> commonly used this, giving the actual f.l. of the camera lens and *also* the
> 35mm equivalent. For example, a magazine article describing an APS camera
> with a 28-56mm lens would also mention that that was 35-70mm in 35mm
> equivalence.
>
> It's the standard and well-established practice, Roger.

And a much argued practice. The confusion caused by this practice
is similar to the confusion by the specifications by the P&S digital
cameras of specifying sensor sizes like 1/1.8" based on vidicon
tubes from the 1950s. The camera manufacturers like the longer focal
lengths because it sounds bigger and more impressive to the consumer,
and then they use the vidicon spec to further confuse the issue so people
do not really know what they are really getting.

See the thread:
[Fwd: A Rant re Focal Length Multipliers] from Jan 24, 2005 in this N.G.
Much of the same discussion we are having. Example:

> Subject: A Rant re Focal Length Multipliers
> From: C Wright <wright9_nojunk@nojunk_mac.com>
> Newsgroups: rec.photo.digital
> Is anyone else bothered by the frequent use of "focal length multipliers" or
> "crop factors" when describing digital cameras and their lenses?

Then see:
The "Multiplier Factor" ... also called the "Crop Factor"
http://www.lonestardigital.com/multipler.htm

Popular Photography a while back which discussed this issue. If I remember
correctly, they concluded "the multiplier" is also a crop factor.

Confusion is common on what the multiplier really means.

Roger
Anonymous
May 25, 2005 5:35:21 PM

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

"Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote in
message news:429402C5.7050003@qwest.net...
> Nostrobino wrote:
>> "Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote
>> in message news:4292AE61.5070804@qwest.net...
>>
>>>You cite the 35mm system as the reference,
>>>then abandon it when it doesn't suit your argument.
>>
>>
>> I "cite the 35mm system as the reference" only in terms of focal length
>> equivalences. This is legitimate because such equivalences have clear
>> meaning for anyone who's been in photography for a while. That's why
>> digital camera manufacturers do it, camera reviewers do it, and
>> photography publications do it.
>>
>> Nor is this something new with digital cameras. The same thing was done
>> when APS cameras came out; the multiplier in that case was 1.25 and
>> publications commonly used this, giving the actual f.l. of the camera
>> lens and *also* the 35mm equivalent. For example, a magazine article
>> describing an APS camera with a 28-56mm lens would also mention that that
>> was 35-70mm in 35mm equivalence.
>>
>> It's the standard and well-established practice, Roger.
>
> And a much argued practice.

I doubt it. Again I point out that it's used by camera manufacturers,
reviewers and publications. It's used because it *makes sense* and is useful
to the photographer. "Crop factor" on the other hand is inexact,
inappropriate, misleading and confusing. You can't crop 1.6 of anything.
When you crop something 0.5 you've removed half of it. When you've cropped
1.0 of it it's all gone and you can't crop any more.

If you insist on using the term "crop factor" then it should be used
correctly. For a 1.6 multiplier the "crop factor" would be 0.375, wouldn't
it? That's the amount you're taking away from the full 35mm frame, LINEARLY.
But wait a minute, you're taking away 60.9% of the AREA. So what's really
the "crop factor," 0.375 or 0.609? But wait a minute, do you take "crop
factor" to refer to WHAT REMAINS, in which case it's either 0.625 or 0.391?

So what's the answer, 0.375, 0.609, 0.625 or 0.609?

Now really, why get into all that silly "crop factor" nonsense at all when
in fact you aren't even talking about actually cropping anything? Simply
referring to a 1.6x multiplier should make it crystal clear to anyone what
is meant.



> The confusion caused by this practice
> is similar to the confusion by the specifications by the P&S digital
> cameras of specifying sensor sizes like 1/1.8" based on vidicon
> tubes from the 1950s.

No, it's nothing like that. I agree with you that those old tube-size
designations have no practical meaning as far as digital cameras are
concerned and serve practically no useful purpose. They're used because
they're the traditional way of describing sensor size, but it seems to me
that is really no excuse for their continued use in this context.



> The camera manufacturers like the longer focal
> lengths because it sounds bigger and more impressive to the consumer,
> and then they use the vidicon spec to further confuse the issue so people
> do not really know what they are really getting.

Roger, you continue to miss the point. It's not a question of manufacturers
trying to make cameras/lenses "more impressive" to the consumer. Anyone who
knows what the numbers mean derives information from them, and those don't
probably don't care, as far as millimeters (actual or equivalent) are
concerned.

Now if you were to make that charge about zoom ratios, where manufacturers
commonly combine optical and digital zooms to give some unrealistically high
zoom range, then I would agree with you. And yes, they do this all the time,
and very prominently too. And it does seem to fool a lot of people. I was
talking to a neighbor about my new Panasonic superzoom with a 12x stabilized
zoom. He pulled out his little cheapo digicam and said, "Mine has a 12 times
zoom too"--and indeed there was a great big sticker on the thing with "12X
ZOOM" in large block letters. Of course what he had was a 3x optical zoom
and 4x digital.

But this is nothing like that. The multiplier is commonly used because it
provides the photographer with exactly the information he wants and needs.
Nothing more or less than that.


>
> See the thread:
> [Fwd: A Rant re Focal Length Multipliers] from Jan 24, 2005 in this N.G.
> Much of the same discussion we are having. Example:
>
> > Subject: A Rant re Focal Length Multipliers
> > From: C Wright <wright9_nojunk@nojunk_mac.com>
> > Newsgroups: rec.photo.digital
> > Is anyone else bothered by the frequent use of "focal length
> > multipliers" or
> > "crop factors" when describing digital cameras and their lenses?
>
> Then see:
> The "Multiplier Factor" ... also called the "Crop Factor"
> http://www.lonestardigital.com/multipler.htm
>
> Popular Photography a while back which discussed this issue. If I
> remember
> correctly, they concluded "the multiplier" is also a crop factor.

I would be surprised and disappointed in Pop Photo if that were true. They
have always used "multiplier" to describe this in the past, ever since the
APS cameras first appeared. I've been a subscriber for many years and never
saw them use "crop factor" in this way, though admittedly I do not read
every issue thoroughly.


>
> Confusion is common on what the multiplier really means.

On the contrary, it's the *least* confusing of all possible ways to describe
what is being described.

N.
Anonymous
May 26, 2005 2:30:25 AM

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

Nostrobino wrote:

>>>It's the standard and well-established practice, Roger.
>>
>>And a much argued practice.
>
> I doubt it.

Well, I guess we will, just have to disagree. But look at a google search.
Here is page one of 242,000 hits. Crop factor is used a lot.

Can a DSLR with a crop factor re-produce a picture taken with a 35 ...
.... That is a DSLR with the crop factor incorporated is a different animal altogether
.... establish and most popular formats in the history of photography. ...
photo.net/bboard/q-and-a-fetch-msg?msg_id=00C2Af - 78k - Cached - Similar pages

Gisle Hannemyr: Crop factor
.... CCD used in a number of popular digital compacts has a crop factor of 4.8x.
.... The crop factor multiplication is just a device to help the photographer ...
heim.ifi.uio.no/~gisle/photo/crop.html - 10k - Cached - Similar pages

Photography: Lenses
.... The 8x enlargement factor is just enough for bird photography, ... designed for
digital cameras with a 1.5x or 1.6x crop factor making them act like a ...
www.wildpicture.com/pages/photography/lenses.htm - 23k - Cached - Similar pages

PHOTOgraphic Magazine Online: Tamron SP AF90mm f/2.8 Di
.... Close-up photography is a popular pastime, for its rewards, ... With the Canon
Digital Rebel and EOS 10D (1.6X crop factor), it crops like a 144mm lens ...
www.photographic.com/lenses/1004tamron/ - 57k - Cached - Similar pages

Why do I need a 50mm?
.... I guess the best way to explain it is that the crop factor is an effective
.... There is an interesting article in Popular Photography (current issue) ...
www.phototakers.com/forum/ ftopic24468.html&view=previous - 72k - Cached - Similar pages

Digital Photography
.... The following are my notes about digital photography, some are general, ...
What it really is, is a crop factor (It cuts off the edges). ...
www.unixhub.com/photo/ - 17k - Cached - Similar pages

First look at Canon’s 16 megapixel EOS-1DS Mark II - Digital ...
.... Popular Photography says that Canon’s 16 megapixel EOS 1Ds Mark II digital
SLR edges ... The crop factor is actually useful when it comes to telephotos, ...
digitalcameras.engadget.com/entry/0400731206341486/ - 40k - Cached - Similar pages

New Digital SLRs from Canon and Nikon - RPPhoto.com
.... This model replaces the popular EOS 10D, which is still available at this ...
with DIGIC II image processor and 8.2 Megapixels (1.6X crop factor vs. ...
www.rpphoto.com/howto/newslrs/default.asp - 34k - Cached - Similar pages

NatureScapes.Net - Article on Underwater Photography: Basic ...
.... Here are a few things to consider before getting into underwater photography.
.... The crop factor of more popular DSLRs makes a 28-105 range zoom very ...
www.naturescapes.net/032004/ss0304.htm - 12k - Cached - Similar pages

Buyer's Guide to Watersports Photography
Buyer's Guide to Watersports Photography. Camera housings, waterproof camera ...
If the crop factor of a digital camera is 1.6 (like the Canon EOS 20D), ...
www.photosupportsystems.com/Support/buyersguide.htm - 7k - Cached - Similar pages
Anonymous
May 26, 2005 5:32:58 AM

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

On Wed, 25 May 2005 13:35:21 -0400, Nostrobino wrote:

> "Crop factor" on the other hand is inexact, inappropriate,
> misleading and confusing. You can't crop 1.6 of anything.
> When you crop something 0.5 you've removed half of it.
> When you've cropped 1.0 of it it's all gone and you can't crop any more.

It may be inexact, but it is appropriate, and not at all
misleading or confusing, except for those whose thinking is focused
so narrowly that they can't see what *most* people have no problem
seeing. Consider eclipses. There are at least two distinct types,
depending on your vantage point. From this planet, there's an
eclipse of the sun and an eclipse of the moon. You might say that
one type uses "cropping" and the other uses "negative cropping".
But the word "eclipse" is common to both. Same with cropping. The
type you're thinking of is different than the type of cropping that
is suggested by a "crop factor", but it's perfectly valid to use the
word "crop" for both, since it allow a person to easily understand
what is going on. Imagine three similar cameras, all using the
same lens mount, one using film with it's standard 24mm x 36mm
images, the second using a sensor of the same size, and a third
using a smaller sensor. If only the first two were sold, "crop
factors" would never have been spoken of. A single lens used on
either of the first two would produce the same images, there would
be no "magnification" or focal length issues. But the same lens
used on the third camera with the smaller sensor couldn't be used to
produce the same pictures. A very simple way of explaining the
difference is to imaging making two opaque masks, the same size as
the small sensor, placing one inside the first camera just above the
film, and the second mask just above the large standard sized
sensor. In both cases, they'd eliminate part of what would have
been recorded on the film and captured by the sensor. What remained
would be the same as what the small sensor captured.

What was eliminated by the masks doesn't have to be done inside
the camera. If it is done in Photoshop, or done after printing by
slicing the print with shears, the effect is the same. The picture
has been "cropped". True, there's no cropping actually occurring in
the camera with the small sensor, but the cropping that occurred in
the other two cameras explains very simply the what's and why's of
what the effect is of using a smaller sensor. The image it sees
(using the same lens) is less than what the other two cameras see
(on the film and on the full sized sensor), by exactly the size of
the "crop" masks that were used. Hence the term "crop factor".


> If you insist on using the term "crop factor" then it should be used
> correctly. For a 1.6 multiplier the "crop factor" would be 0.375,
> wouldn't it? That's the amount you're taking away from the full 35mm
> frame, LINEARLY.
> But wait a minute, you're taking away 60.9% of the AREA. So what's really
> the "crop factor," 0.375 or 0.609? But wait a minute, do you take "crop
> factor" to refer to WHAT REMAINS, in which case it's either 0.625 or 0.391?
>
> So what's the answer, 0.375, 0.609, 0.625 or 0.609?
>
> Now really, why get into all that silly "crop factor" nonsense at all when
> in fact you aren't even talking about actually cropping anything? Simply
> referring to a 1.6x multiplier should make it crystal clear to anyone what
> is meant.

Do you really think you've help clarify anything by the above? If
that was shown to most people in a camera store the general reaction
wouldn't be "oh my, how perfectly clear". It would instead more
likely be "that guy ought to get of the soap box and learn to speak
English!" All the ranting in the world won't stop people from using
imprecise or illogical terms. Mentioning your preference once or
twice is no problem. But making a crusade out of it is quite
something else. Until the day arrives when Esperanto is the
universal language, it would be better to accept what isn't likely
to be changed, and help explain away misunderstandings and
misconceptions other might have, rather than howling at the moon.
Anonymous
May 26, 2005 4:42:46 PM

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

"ASAAR" <caught@22.com> wrote in message
news:24la915alavps69nvg0t110cs647qb7hvv@4ax.com...
> On Wed, 25 May 2005 13:35:21 -0400, Nostrobino wrote:
>
>> "Crop factor" on the other hand is inexact, inappropriate,
>> misleading and confusing. You can't crop 1.6 of anything.
>> When you crop something 0.5 you've removed half of it.
>> When you've cropped 1.0 of it it's all gone and you can't crop any more.
>
> It may be inexact, but it is appropriate, and not at all
> misleading or confusing, except for those whose thinking is focused
> so narrowly that they can't see what *most* people have no problem
> seeing.

It's both inexact and inappropriate. Nothing is being cropped. By "*most*
people" you apparently mean those people who use the term "crop factor" when
they mean "multiplier." I certainly agree that people "have no problem"
using terms incorrectly when they habitually use those terms incorrectly.
(Duh.)


> Consider eclipses. There are at least two distinct types,
> depending on your vantage point. From this planet, there's an
> eclipse of the sun and an eclipse of the moon. You might say that
> one type uses "cropping" and the other uses "negative cropping".
> But the word "eclipse" is common to both. Same with cropping. The
> type you're thinking of is different than the type of cropping that
> is suggested by a "crop factor", but it's perfectly valid to use the
> word "crop" for both, since it allow a person to easily understand
> what is going on. Imagine three similar cameras, all using the
> same lens mount, one using film with it's standard 24mm x 36mm
> images, the second using a sensor of the same size, and a third
> using a smaller sensor. If only the first two were sold, "crop
> factors" would never have been spoken of.

And what a better world it would be if that were only the case. :-/


> A single lens used on
> either of the first two would produce the same images, there would
> be no "magnification" or focal length issues. But the same lens
> used on the third camera with the smaller sensor couldn't be used to
> produce the same pictures. A very simple way of explaining the
> difference is to imaging making two opaque masks, the same size as
> the small sensor, placing one inside the first camera just above the
> film, and the second mask just above the large standard sized
> sensor. In both cases, they'd eliminate part of what would have
> been recorded on the film and captured by the sensor. What remained
> would be the same as what the small sensor captured.

There is no argument or misunderstanding about any of that. We are in full,
complete, absolute 100% agreement that a smaller sensor behind the same lens
will collect less of the image. Yes, masking off part of the film would
produce the same result, and in fact there have been cameras sold with masks
to do exactly that. I think we can safely take that as common ground and
move on from there.


>
> What was eliminated by the masks doesn't have to be done inside
> the camera. If it is done in Photoshop, or done after printing by
> slicing the print with shears, the effect is the same. The picture
> has been "cropped".

In the case of Photoshop, shears or under the enlarger, yes. Absolutely. If
you print only part of the image that's *available for printing* you have
ipso facto cropped out the rest.


> True, there's no cropping actually occurring in
> the camera with the small sensor,

I wish you could have put that in 36-point bold flashing red type. That is
the whole crux of the matter. THERE'S NO CROPPING ACTUALLY OCCURRING IN THE
CAMERA WITH THE SMALL SENSOR. Right! Correct! Absolutely! Eureka!
Hallelujah! (And whatever similar ejaculations may come to mind.)

Say it again! THERE'S NO CROPPING ACTUALLY OCCURRING IN THE CAMERA WITH THE
SMALL SENSOR.

And again! THERE'S NO CROPPING ACTUALLY OCCURRING IN THE CAMERA WITH THE
SMALL SENSOR.


> but the cropping that occurred in
> the other two cameras

Whoa. *No* cropping "occurred in the other two cameras." The film was masked
to produce a smaller negative. That isn't cropping. Cropping is something
you do *after* the image has been processed (whether in a developing tank or
in a digital camera, makes no difference) to select some smaller part of it.

I am using "crop" in the way it has always been used in general photography.
It is something the photographer does to the complete image *as recorded*.
It isn't something that's done in the camera, though under some really weird
and unusual circumstances I suppose it might be.

If you have an image recorded by a smaller sensor, that's it, that's the
image. It isn't cropped unless and until you crop it yourself (or someone
does).


> explains very simply the what's and why's of
> what the effect is of using a smaller sensor. The image it sees
> (using the same lens) is less than what the other two cameras see
> (on the film and on the full sized sensor), by exactly the size of
> the "crop" masks that were used. Hence the term "crop factor".

As already explained, that is not cropping.


>
>
>> If you insist on using the term "crop factor" then it should be used
>> correctly. For a 1.6 multiplier the "crop factor" would be 0.375,
>> wouldn't it? That's the amount you're taking away from the full 35mm
>> frame, LINEARLY.
>> But wait a minute, you're taking away 60.9% of the AREA. So what's really
>> the "crop factor," 0.375 or 0.609? But wait a minute, do you take "crop
>> factor" to refer to WHAT REMAINS, in which case it's either 0.625 or
>> 0.391?
>>
>> So what's the answer, 0.375, 0.609, 0.625 or 0.609?
>>
>> Now really, why get into all that silly "crop factor" nonsense at all
>> when
>> in fact you aren't even talking about actually cropping anything? Simply
>> referring to a 1.6x multiplier should make it crystal clear to anyone
>> what
>> is meant.
>
> Do you really think you've help clarify anything by the above?

What it was meant to clarify was the complete inappropriateness, inaccuracy
and uselessness of the term "crop factor." I hope it has clarified that. I
had no other goal in mind.


> If
> that was shown to most people in a camera store the general reaction
> wouldn't be "oh my, how perfectly clear".

I should hope not.


> It would instead more
> likely be "that guy ought to get of the soap box and learn to speak
> English!"

It is in English, and concisely put too if I say so myself. Your complaint
is not really with the explanation, but with the fact that it explains the
silliness of the misusage to which you are for some reason attached. I can't
help your unhappiness with that.


> All the ranting in the world won't stop people from using
> imprecise or illogical terms.

Actually explanations do sometimes correct such misusage, and sometimes they
don't. Obviously that depends on the listener or reader. Some people are
impervious to reason and the more carefully their errors are explained to
them, the more stubbornly they will stand by those errors. I can't help that
either. All I can do is point out the facts in the hope that some readers,
including newbies who might otherwise be corrupted, will either abandon this
really silly misusage or not adopt it in the first place. So that's all I
do.

N.
Anonymous
May 26, 2005 6:10:38 PM

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

"Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote in
message news:429550E1.3000700@qwest.net...
> Nostrobino wrote:
>
>>>>It's the standard and well-established practice, Roger.
>>>
>>>And a much argued practice.
>>
>> I doubt it.
>
> Well, I guess we will, just have to disagree. But look at a google
> search.
> Here is page one of 242,000 hits. Crop factor is used a lot.

I am not surprised.

The problem there is that the Internet has become such a wonderful
instrument for the propagation of misinformation. Anyone can set up a Web
page containing some mixture of fact and fiction, or some amount of
nonsense, and many people do.

The pages you mention and link to are hardly what I would call authoritative
sources.

Show me some pages from, say, Canon that use "crop factor" in your way and
I'll pay attention.

Or from Nikon.

Or from Minolta.

Or from Pentax.

Or from Olympus.

In fact, has *any* major camera manufacturer ever used "crop factor" in the
way you use it?

What you call a "crop factor" is in fact simply a multiplier. Why you and
some others have this devotion to "crop factor" I have no idea. Perhaps you
think it has a nice technical or mathematical sound to it. Some people love
jargon for the sake of jargon and don't really seem to care much whether the
term used accurately describes what they're trying to describe.

Look: My state has a sales tax of 6%. In order to figure sales tax on
something I multiply the price by 1.06. Now is that number 1.06 a "crop
factor"? No, it's a multiplier. Does anyone call it a "crop factor"? I doubt
it. Would calling it a "crop factor" make it more clear to anyone? I hardly
think so.

Now what you call a "crop factor" is in fact a multiplier in exactly that
same way. When you say a camera has a "crop factor" of 1.6, what you really
mean is you have to multiply the actual focal length of the lens used by 1.6
to get the *effective* focal length in familiar 35mm terms. Correct? So the
number 1.6 is a multiplier. Correct? It has no other use than to multiply
something to get some result. Does it?

If you think in this case that number 1.6 has some *other* use than simply
to serve as a multiplier, please tell me what you think that other use might
be.

Waiting . . . < tick tick tick tick tick >

N.
Anonymous
May 27, 2005 12:43:41 PM

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

Nostrobino wrote:
> "Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote in
> message news:429550E1.3000700@qwest.net...
>
>>Nostrobino wrote:
>>
>>
>>>>>It's the standard and well-established practice, Roger.
>>>>
>>>>And a much argued practice.
>>>
>>>I doubt it.
>>
>>Well, I guess we will, just have to disagree. But look at a google
>>search.
>>Here is page one of 242,000 hits. Crop factor is used a lot.
>
>
> I am not surprised.
>
> The problem there is that the Internet has become such a wonderful
> instrument for the propagation of misinformation. Anyone can set up a Web
> page containing some mixture of fact and fiction, or some amount of
> nonsense, and many people do.
>
> The pages you mention and link to are hardly what I would call authoritative
> sources.
>
> Show me some pages from, say, Canon that use "crop factor" in your way and
> I'll pay attention.
>
> Or from Nikon.
>
> Or from Minolta.
>
> Or from Pentax.
>
> Or from Olympus.
>
> In fact, has *any* major camera manufacturer ever used "crop factor" in the
> way you use it?
>
> What you call a "crop factor" is in fact simply a multiplier. Why you and
> some others have this devotion to "crop factor" I have no idea. Perhaps you
> think it has a nice technical or mathematical sound to it. Some people love
> jargon for the sake of jargon and don't really seem to care much whether the
> term used accurately describes what they're trying to describe.
>
> Look: My state has a sales tax of 6%. In order to figure sales tax on
> something I multiply the price by 1.06. Now is that number 1.06 a "crop
> factor"? No, it's a multiplier. Does anyone call it a "crop factor"? I doubt
> it. Would calling it a "crop factor" make it more clear to anyone? I hardly
> think so.
>
> Now what you call a "crop factor" is in fact a multiplier in exactly that
> same way. When you say a camera has a "crop factor" of 1.6, what you really
> mean is you have to multiply the actual focal length of the lens used by 1.6
> to get the *effective* focal length in familiar 35mm terms. Correct? So the
> number 1.6 is a multiplier. Correct? It has no other use than to multiply
> something to get some result. Does it?
>
> If you think in this case that number 1.6 has some *other* use than simply
> to serve as a multiplier, please tell me what you think that other use might
> be.
>
> Waiting . . . < tick tick tick tick tick >
>
> N.
>
>

The camera manufacturers do not
call it a multiplier either. Canon, for example, doesn't talk about
it on the web sites or product specs that I have seen. Similarly,
they won't tell you what a 1/1.8" sensor is either. They won't tell
you what the MTF of a scanner is either.

See some professional photography sites.

Understanding the DSLR Magnification Factor
http://luminous-landscape.com/tutorials/understanding-s...

Field Of View crop
"One thing it is important to understand is Field of View crop. ...
This used to be referred
to as 'focal length multiplier' although this term is actually
inaccurate as it is not a multiplication but a crop, we prefer to
refer to it as Field Of View crop (FOV crop). "
http://www.dpreview.com/reviews/canoneos300d/page16.asp

"the small sensor gives an effective 1.6x "multiplier" (actually crop factor)..."
http://www.bobatkins.com/photography/reviews/fisheye.ht...

"With the advent of Digital SLR Camera Bodies, the term
Field of View Crop Factor has come our world. The source of
this term is the smaller-than-35mm sensor present in many of
Canon and other manufacturers' DSLR sensors. Canon's EF Lenses
still focus the image on the same plane as before, but sensors
smaller than 35mm sensors do not capture the entire image. Thus,
the image is "cropped". The Field of View Crop Factor
(FOVCF from here on) refers to the amount of the image that is cropped. "
http://www.the-digital-picture.com/Canon-Lenses/Field-o...

The problem with focal length multiplier is that it has implications
for depth of field and resolution, which do not change with the
smaller sensors. You confuse crop factor with multiplier. The crop factor
is a "Field of View Crop Factor" so,

the field of view = 35mm full frame field of view / crop factor.

Roger
Anonymous
May 27, 2005 7:39:30 PM

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

"Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote in
message news:4297321D.2030304@qwest.net...
> Nostrobino wrote:
>> "Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote
>> in message news:429550E1.3000700@qwest.net...
>>
>>>Nostrobino wrote:
>>>
>>>
>>>>>>It's the standard and well-established practice, Roger.
>>>>>
>>>>>And a much argued practice.
>>>>
>>>>I doubt it.
>>>
>>>Well, I guess we will, just have to disagree. But look at a google
>>>search.
>>>Here is page one of 242,000 hits. Crop factor is used a lot.
>>
>>
>> I am not surprised.
>>
>> The problem there is that the Internet has become such a wonderful
>> instrument for the propagation of misinformation. Anyone can set up a Web
>> page containing some mixture of fact and fiction, or some amount of
>> nonsense, and many people do.
>>
>> The pages you mention and link to are hardly what I would call
>> authoritative sources.
>>
>> Show me some pages from, say, Canon that use "crop factor" in your way
>> and I'll pay attention.
>>
>> Or from Nikon.
>>
>> Or from Minolta.
>>
>> Or from Pentax.
>>
>> Or from Olympus.
>>
>> In fact, has *any* major camera manufacturer ever used "crop factor" in
>> the way you use it?
>>
>> What you call a "crop factor" is in fact simply a multiplier. Why you and
>> some others have this devotion to "crop factor" I have no idea. Perhaps
>> you think it has a nice technical or mathematical sound to it. Some
>> people love jargon for the sake of jargon and don't really seem to care
>> much whether the term used accurately describes what they're trying to
>> describe.
>>
>> Look: My state has a sales tax of 6%. In order to figure sales tax on
>> something I multiply the price by 1.06. Now is that number 1.06 a "crop
>> factor"? No, it's a multiplier. Does anyone call it a "crop factor"? I
>> doubt it. Would calling it a "crop factor" make it more clear to anyone?
>> I hardly think so.
>>
>> Now what you call a "crop factor" is in fact a multiplier in exactly that
>> same way. When you say a camera has a "crop factor" of 1.6, what you
>> really mean is you have to multiply the actual focal length of the lens
>> used by 1.6 to get the *effective* focal length in familiar 35mm terms.
>> Correct? So the number 1.6 is a multiplier. Correct? It has no other use
>> than to multiply something to get some result. Does it?
>>
>> If you think in this case that number 1.6 has some *other* use than
>> simply to serve as a multiplier, please tell me what you think that other
>> use might be.
>>
>> Waiting . . . < tick tick tick tick tick >
>>
>> N.
>
> The camera manufacturers do not
> call it a multiplier either. Canon, for example, doesn't talk about
> it on the web sites or product specs that I have seen.

You're exactly right there. Minolta doesn't either, in any of their
literature I've seen. Why they don't address this I don't know; it surprises
me.



> Similarly,
> they won't tell you what a 1/1.8" sensor is either. They won't tell
> you what the MTF of a scanner is either.

I wouldn't expect them to get into discussions of MTF, but I would agree
with you that they should give more useful information as to sensor size. It
seems ridiculous to me that the manufacturers continue to use terms like
1/1.8" for this, when that does not actually describe sensor size in any
meaningful way.


>
> See some professional photography sites.
>
> Understanding the DSLR Magnification Factor
> http://luminous-landscape.com/tutorials/understanding-s...

"Magnification factor" I have no problem with. Just another way of saying
"multiplier."


>
> Field Of View crop
> "One thing it is important to understand is Field of View crop. ...

My objection continues to be that this is a nonstandard use of the term
"crop."


> This used to be referred
> to as 'focal length multiplier' although this term is actually
> inaccurate as it is not a multiplication but a crop, we prefer to
> refer to it as Field Of View crop (FOV crop). "

This seems to me a completely unnecessary misunderstanding of the term
"focal length multiplier." CORRECT, the actual focal length is not
multiplied; ergo, there is no f.l. multiplier in the sense of, say, a tele
extender for an SLR lens. I don't really think anyone who knows enough about
photographic optics to have any understanding of such a term in the first
place *thinks* that's what it means in the case of a digital SLR. All it
means is "multiplier applied to the actual focal length to find 35mm
equivalence in terms of field of view." Since that's rather unwieldy, some
shorter term clearly is needed, but it should be some reasonably accurate
term, which "crop factor" is not. I think simply "multiplier" serves well
enough when the context makes the meaning plain. When that's not enough,
"multiplier for 35mm equivalence" should be sufficient. It shouldn't have to
be used too often.


> http://www.dpreview.com/reviews/canoneos300d/page16.asp
>
> "the small sensor gives an effective 1.6x "multiplier" (actually crop
> factor)..."
> http://www.bobatkins.com/photography/reviews/fisheye.ht...
>
> "With the advent of Digital SLR Camera Bodies, the term
> Field of View Crop Factor has come our world. The source of
> this term is the smaller-than-35mm sensor present in many of
> Canon and other manufacturers' DSLR sensors. Canon's EF Lenses
> still focus the image on the same plane as before, but sensors
> smaller than 35mm sensors do not capture the entire image. Thus,
> the image is "cropped". The Field of View Crop Factor
> (FOVCF from here on) refers to the amount of the image that is cropped. "
> http://www.the-digital-picture.com/Canon-Lenses/Field-o...

Well, "field of view crop factor" is a little better than just "crop factor"
because it's more specific, and implies something quite different from just
selecting some part of a photograph for final use, which is what "crop"
means. So it's still a nonstandard use of "crop."


>
> The problem with focal length multiplier is that it has implications
> for depth of field and resolution, which do not change with the
> smaller sensors.

Actually, they do. Are you assuming that depth of field remains the same for
any actual focal length and f-stop regardless of format size? That is not
true. Many people seem to forget (or were never aware) that depth of field
also changes with *final magnification*. Some people evidently look at the
DoF scale engraved on a lens body and think that's set in cement, that
that's *absolutely* what the DoF is.

Depth of field calculations are based on some acceptable blur circle size,
which is fairly arbitrary. For most Japanese 35mm cameras, if I remember
correctly the critical blur circle is considered to be .033 mm or
thereabouts. Any blur circle smaller than that is "sharp" (i.e., within the
depth of field) and anything larger than that is "unsharp" (outside the
DoF). German makers generally used a more relaxed standard (larger blur
circle) and so, for example, a German 50mm lens would show more DoF on its
engraved scale, for any given f-stop and distance, than would a Japanese
50mm lens. Of course that did not mean the German lens *actually* had more
depth of field, only that the assumptions used to calculate it were
different.

The more an image is enlarged, the more everything in it is enlarged,
including the blur circle. The result of this of course is that depth of
field *shrinks* with greater enlargement. Very small prints often appear
sharp in places that are not sharp at all in larger sized prints. An extreme
example of this is the LCD monitor on your camera, on which images often
look nice and sharp where they are terribly unsharp on a larger monitor or
print. Many digital cameras in manual focusing mode enlarge part of the
monitor image greatly to deal with this.

Now obviously for digital cameras with a smaller than 24 x 36 sensor,
enlargement will be greater than with a full-frame 35 using the same lens.
So the DoF scale on a FFL lens which may have been perfectly suitable (for a
given print size) on a 35mm camera, will no longer be accurate on a digital
SLR. And the greater the difference in sensor size, the greater the
difference in DoF.


> You confuse crop factor with multiplier. The crop factor
> is a "Field of View Crop Factor" so,
>
> the field of view = 35mm full frame field of view / crop factor.

Wanna bet?

A 17mm lens on a full-frame 35 covers about 103.6 degrees corner to corner.
This is assuming the full 43.2mm diagional (24 x 36 negative).

Now if your belief were correct, that same 17mm lens on a "1.6 crop factor"
camera would cover about 103.6 / 1.6 = 64.75 degrees corner to corner.
That's just slightly more than a 35mm lens on a full-frame 35 (which is
about 63.4 degrees).

But in fact, taking the sensor size to have a diagonal of 43.2 / 1.6 = 27mm,
that 17mm lens would cover about 76.9 degrees corner to corner, or slightly
more than a 28mm lens on a full-frame 35 (which is about 75.3 degrees).

(Feel free to check my geometry on this.)

Now apply the 1.6 multiplier to the 17mm lens and see what you get. I get
27.2mm, which comports perfectly with the use of that 1.6 as a simple
multiplier to get 35mm focal length equivalence. That is, a field of view
slightly wider than a 28mm lens. It is nowhere near what your "crop factor"
approach predicts.

N.
Anonymous
May 27, 2005 8:03:23 PM

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

"Roger N. Clark (change username to rnclark)" <username@qwest.net> wrote in
message news:4297321D.2030304@qwest.net...
[ . . . ]
> Field Of View crop
> "One thing it is important to understand is Field of View crop. ...
> This used to be referred
> to as 'focal length multiplier' although this term is actually
> inaccurate as it is not a multiplication but a crop, we prefer to
> refer to it as Field Of View crop (FOV crop). "
> http://www.dpreview.com/reviews/canoneos300d/page16.asp

Roger, by the way, I have just now been to the DPReview site, and they
appear to be using *both* terms interchangeably. The Canon Rebel XT specs
page (Febrary '05) uses the term "focal length multiplier."
http://www.dpreview.com/reviews/specs/Canon/canon_eos35...

The full Rebel XT review (April '05) uses "field of view crop."
http://www.dpreview.com/reviews/canoneos350d/page2.asp

The page you've linked to is from September '03, so it's not just a recent
change on their part. It looks to me like they haven't made up their minds
what they want to call it.

N.
Anonymous
May 27, 2005 9:05:51 PM

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

On Fri, 27 May 2005 15:39:30 -0400, Nostrobino wrote:

> Depth of field calculations are based on some acceptable
> blur circle size, which is fairly arbitrary. For most Japanese
> 35mm cameras, if I remember correctly the critical blur circle
> is considered to be .033 mm or thereabouts. Any blur circle
> smaller than that is "sharp" (i.e., within the depth of field)
> and anything larger than that is "unsharp" (outside the DoF).

An old photo handbook shows that the size of the blur circle,
while perhaps slightly arbitrary, can have many different sizes
because it depends on, among other things, print size and viewing
distance. The representative blur circle size it gives is 0.25mm,
which is based on a contact print viewed at a distance of 250mm. It
then calculates another one that is very close to your figure. The
handbook probably prededates the term "blur circle", using one I'm
more familiar with from old photo books. The handbook says*:

:> If you intend to enlarge the film image, or view it more closely,
:> then the circle of confusion will become smaller:
:>
:> c = (v * D) / (1000 * S)
:>
:> For example, how big should the circle of confusion be for a 35mm
:> negative that will be enlarged to make an 8x10in (20x25cm) print
:> and viewed at normal distances?

It then plugs into the formula the values:
v = negative size (width) = 36mm
D = print viewing distance = 250mm
S = print size (width) = 250mm
which results in a circle confusion of
c = (36mm * 250mm) / ( 1000 * 250mm) = 0.036mm

It then concludes with:

:> Most optical calculations assume fixed values for the
:> circle of confusion, and unless you plan to make
:> billboard-sized prints to be viewed close-to, you can use
:> figures of 0.036mm for 35mm film, and 0.127mm for roll film.

I won't add to the overall confusion by comparing blur circles
with crop circles, although I'll add that the viewing distance for
than latter is much larger than anything normally used in blur
circle calculations. :) 
Anonymous
May 27, 2005 11:58:04 PM

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

"ASAAR" <caught@22.com> wrote in message
news:ah0f91hcn9798fikgnulg5gqss4rb2gok1@4ax.com...
> On Fri, 27 May 2005 15:39:30 -0400, Nostrobino wrote:
>
>> Depth of field calculations are based on some acceptable
>> blur circle size, which is fairly arbitrary. For most Japanese
>> 35mm cameras, if I remember correctly the critical blur circle
>> is considered to be .033 mm or thereabouts. Any blur circle
>> smaller than that is "sharp" (i.e., within the depth of field)
>> and anything larger than that is "unsharp" (outside the DoF).
>
> An old photo handbook shows that the size of the blur circle,
> while perhaps slightly arbitrary, can have many different sizes
> because it depends on, among other things, print size and viewing
> distance. The representative blur circle size it gives is 0.25mm,
> which is based on a contact print viewed at a distance of 250mm. It
> then calculates another one that is very close to your figure. The
> handbook probably prededates the term "blur circle", using one I'm
> more familiar with from old photo books. The handbook says*:
>
> :> If you intend to enlarge the film image, or view it more closely,
> :> then the circle of confusion will become smaller:
> :>
> :> c = (v * D) / (1000 * S)
> :>
> :> For example, how big should the circle of confusion be for a 35mm
> :> negative that will be enlarged to make an 8x10in (20x25cm) print
> :> and viewed at normal distances?

Yes, "circle of confusion" is the older term I'm quite sure, as I remember
seeing that used many years ago. I haven't seen it for quite a while though
I'm sure it's still appropriate. I have an old book myself, Cox's
"Photographic Optics," which also has several equations for depth of field.
Cox calls it the "disc of confusion." The book is so old it gives most focal
lengths in inches ( ! ).

Whatever the blob is called, for depth-of-field calculations of course it's
a theoretical perfect-lens thing, not taking coma or other lens aberrations
into consideration which in the real world would make the circle of
confusion slightly larger. The difference, I suppose, is too small to worry
about.


>
> It then plugs into the formula the values:
> v = negative size (width) = 36mm
> D = print viewing distance = 250mm
> S = print size (width) = 250mm
> which results in a circle confusion of
> c = (36mm * 250mm) / ( 1000 * 250mm) = 0.036mm

Quite so; viewing distance is as important as, and at least to some extent
cancels out, greater enlargement, since really large prints are usually
viewed at more than ordinary reading distance. So right, the viewing
distance really should be included in the final enlargement calculation, the
greater the viewing distance the less the effective final enlargement and
the greater the apparent depth of field.


>
> It then concludes with:
>
> :> Most optical calculations assume fixed values for the
> :> circle of confusion, and unless you plan to make
> :> billboard-sized prints to be viewed close-to, you can use
> :> figures of 0.036mm for 35mm film, and 0.127mm for roll film.
>
> I won't add to the overall confusion by comparing blur circles
> with crop circles, although I'll add that the viewing distance for
> than latter is much larger than anything normally used in blur
> circle calculations. :) 

:-)

N.
Anonymous
May 28, 2005 2:12:41 AM

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

Nostrobino wrote:
> It's both inexact and inappropriate. Nothing is being cropped.

A smaller piece is being cropped from the same circlular lens
projection. It is a crop factor, not a magnifier.

That's why you don't need to use a faster shutter speed than the base
(uncropped) focal length while trying to control camera shake when
using a cropper. The rule of thumb remains 1/focal length of the base
lens, before any crop factor is applied. Just as cropping away the
outer frame of a print doesn't increase image blur.

That's why DOF discrimination suffers with a cropping DSLR, the outer
frame (much of the blurred DOF) gets cropped away.

That's why optical quality skyrockets when using a cropping DSLR
compared to using a FF DSLR, even when using a wider lens to produce
the same apparent FOV. True corner-to-corner (uncropped) image quality
in 35mm format lenses is terribly poor when compared to a very small
central portion of the same lens projection.
Anonymous
May 28, 2005 1:10:48 PM

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

<george_preddy@yahoo.com> wrote in message
news:1117257161.155556.244630@g14g2000cwa.googlegroups.com...
>
> Nostrobino wrote:
>> It's both inexact and inappropriate. Nothing is being cropped.
>
> A smaller piece is being cropped from the same circlular lens
> projection. It is a crop factor, not a magnifier.

Maybe with Sigma cameras, which apparently do everything differently. With
reputable cameras it is not a "crop factor." ;-)


>
> That's why you don't need to use a faster shutter speed than the base
> (uncropped) focal length while trying to control camera shake when
> using a cropper. The rule of thumb remains 1/focal length of the base
> lens, before any crop factor is applied.

Multiplier, you mean. Anyway, not true. The only reason for the 1/focal
length rule of thumb (which is not set in cement anyway) is that increased
focal length = increased magnification = more obvious blur from camera
movement. All things being equal, shooting with a 50mm lens at 1/50 second
should produce the same amount of *angular* blur (at the subject) from
camera shake as with any other f.l. lens at the same shutter speed. But with
a 500mm lens that blur would be magnified ten times and therefore much more
noticeable, depending of course on the degree of final enlargement.

The same principle obtains with the digital camera multiplier. Following the
rule of thumb, if you needed 1/300 second with a 300mm lens, then you would
also need 1/300 with a 200mm lens and a 1.5x multiplier. They would be
effectively the same thing, for the same degree of final enlargement.


> Just as cropping away the
> outer frame of a print doesn't increase image blur.

Because you have not changed the degree of final enlargement. If you crop
part of the print and then enlarge that result to the same size as the
original, you *will* increase blur.


>
> That's why DOF discrimination suffers with a cropping DSLR, the outer
> frame (much of the blurred DOF) gets cropped away.
>
> That's why optical quality skyrockets when using a cropping DSLR
> compared to using a FF DSLR, even when using a wider lens to produce
> the same apparent FOV. True corner-to-corner (uncropped) image quality
> in 35mm format lenses is terribly poor when compared to a very small
> central portion of the same lens projection.

True that all lenses deliver better sharpness in the center of the field
than at the edges, but it does not necessarily fall off evenly from center
to edge as you seem to be assuming. My understanding (which admittedly is
dim in this area) is that digital sensors give better results when the
image-forming rays are as perpendicular to them as possible, and
digital-camera lenses are designed with this in mind. It follows of course
that at the corners of a small digital sensor, these rays are closer to the
perpendicular than would be the case with a larger sensor.

N.
Anonymous
May 28, 2005 8:30:21 PM

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

<george_preddy@yahoo.com> wrote in message
news:1117257161.155556.244630@g14g2000cwa.googlegroups.com...
>
> Nostrobino wrote:
>> It's both inexact and inappropriate. Nothing is being cropped.
>
> A smaller piece is being cropped from the same circlular lens
> projection. It is a crop factor, not a magnifier.
>
> That's why you don't need to use a faster shutter speed than
> the base (uncropped) focal length while trying to control camera
> shake when using a cropper.

You do if you want to get the same image size, which would require
magnification (of camera shake and DoF blur) of the cropped image.

> The rule of thumb remains 1/focal length of the base
> lens, before any crop factor is applied.

Multipied by the crop factor if you need to magnify for same size
output.

> Just as cropping away the outer frame of a print doesn't increase
> image blur.

Indeed, it results in a smaller image. Reducing the size of an
uncropped image by resampling likewise reduces the size of de-focus an
camera shake blur.

> That's why DOF discrimination

???

> suffers with a cropping DSLR, the outer frame (much of the blurred
> DOF) gets cropped away.

Resulting is a smaller Field of View which, if compensated for by a
smaller focal length, will result in larger DoF.

> That's why optical quality skyrockets when using a cropping
> DSLR compared to using a FF DSLR, even when using a wider
> lens to produce the same apparent FOV.

Double wrong.
1. Wider angle lenses are on average harder to to correct for
aberrations (even on a cropped image circle, the lens' edge rays also
contribute to the image centre). It takes a reduced diameter design
(or closing down the aperture) to avoid that. The more complicated
design of wider angle lenses also one of the reasons why the best lens
quality can usually be fount in the 100 to 400mm range of lenses
(specialty lenses aside).
2. For the same FoV and the same output size, the cropped version
needs to be magnified, or the un-cropped version needs to
down-sampled. That means that the blur gets magnified for the cropped
image, or reduced for the full frame image.

> True corner-to-corner (uncropped) image quality in 35mm format
> lenses is terribly poor when compared to a very small central
> portion of the same lens projection.

That depends on the lens ...

Bart
Anonymous
May 29, 2005 5:55:36 AM

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

In message <1117257161.155556.244630@g14g2000cwa.googlegroups.com>,
george_preddy@yahoo.com wrote:

>That's why optical quality skyrockets when using a cropping DSLR
>compared to using a FF DSLR, even when using a wider lens to produce
>the same apparent FOV. True corner-to-corner (uncropped) image quality
>in 35mm format lenses is terribly poor when compared to a very small
>central portion of the same lens projection.

That's very nice, but if you intend to view the images at the same size,
then the resolution of the center of the focal plane has to stretch by
the crop factor. So, let's say a "full frame" resolution is 800 line
pairs per picture height with 50% contrast; with a 1/1.6 crop, it drops
to 500 line pairs per picture height with 50% contrast. You don't gain
by cropping; you lose, generally. All you can do is avoid corners that
go *really* bad, but the areas you do keep get *SOFTER*, scaled to
actual usage.
--

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John P Sheehy <JPS@no.komm>
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Anonymous
May 29, 2005 6:07:27 AM

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

In message <42988108$0$17153$e4fe514c@news.xs4all.nl>,
"Bart van der Wolf" <bvdwolf@no.spam> wrote:

>> The rule of thumb remains 1/focal length of the base
>> lens, before any crop factor is applied.
>
>Multipied by the crop factor if you need to magnify for same size
>output.

Of course, this whole rule of thumb applies only literally to subjects
at infinity. Objects very close to the lens can't follow this rule; the
real issue is magnification. You can't hand-hold a 50mm macro (with
ambient light) at 1/50 on a 35mm "full-frame", or 1/80 with a 1/1.6
crop, if the magnification is 1:1! You need to use something like 1/250
to 1/500. That's why so many people's macro attempts come out so
poorly; they try to apply a rule of thumb when it doesn't apply.

Hand-holdability is directly related to magnification of the subject.
The same goes for DOF; for any given film or sensor, to be printed or
viewed at the same size, DOF is related directly to f-stop and
magnification.

Lots of bad decisions are made because these basic facts are ignored, in
favor of "rules of thumb" that don't apply in many situations.
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John P Sheehy <JPS@no.komm>
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May 29, 2005 10:30:59 AM

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

> ...
> Hand-holdability is directly related to magnification of the subject.
> ...

Hand-holdability is directly related to a
camera operator's ability to hold it still.

Jeff (shakey hands...normal rules do not apply)
Anonymous
May 29, 2005 6:56:41 PM

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

In message <08oi9194rpua9nqq04gqvj95qt8nb5psl0@4ax.com>,
Confused <somebody@someplace.somenet> wrote:

>> ...
>> Hand-holdability is directly related to magnification of the subject.
>> ...

>Hand-holdability is directly related to a
>camera operator's ability to hold it still.

Well, yes; make that "for any given person, using a given camera ...".
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John P Sheehy <JPS@no.komm>
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!