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Equivalent focal lengths

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Anonymous
December 17, 2004 2:08:21 AM

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

I currently have a Nikon 35mm SLR, so when I get a digital SLR, it will
also be a Nikon so I can interchange the lenses between the cameras.
I'm pretty much settled on the D70.

My question is, if I put my current 50mm on a D7, what would its
equivalent focal length to a 35mm camera be?

--
Stop Mad Cowboy Disease: Impeach the son of a Bush.
Anonymous
December 17, 2004 9:16:22 AM

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

Michelle Steiner wrote:

> I currently have a Nikon 35mm SLR, so when I get a digital SLR, it will
> also be a Nikon so I can interchange the lenses between the cameras.
> I'm pretty much settled on the D70.
>
> My question is, if I put my current 50mm on a D7, what would its
> equivalent focal length to a 35mm camera be?
>
It'd be equal to a 75mm lens.

--
John McWilliams
Anonymous
December 17, 2004 9:16:23 AM

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

In article <WQuwd.513700$wV.141735@attbi_s54>,
John McWilliams <jpmcw@comcast.net> wrote:

> > My question is, if I put my current 50mm on a D7, what would its
> > equivalent focal length to a 35mm camera be?
> >
> It'd be equal to a 75mm lens.

Thanks.

Does that 1.5 : 1 ratio hold true for all focal lengths? Would my 85 mm
lens be equivalent to a 127.5 mm lens?

--
Stop Mad Cowboy Disease: Impeach the son of a Bush.
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Anonymous
December 17, 2004 10:15:49 AM

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

Michelle Steiner wrote:
> I currently have a Nikon 35mm SLR, so when I get a digital SLR, it will
> also be a Nikon so I can interchange the lenses between the cameras.
> I'm pretty much settled on the D70.
> My question is, if I put my current 50mm on a D7, what would its
> equivalent focal length to a 35mm camera be?

75 mm (roughly, as the multiplier is not exactly
but very close to 1.5 x)


Juergen
Anonymous
December 17, 2004 11:12:07 AM

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

Michelle Steiner wrote:
> John McWilliams <jpmcw@comcast.net> wrote:
> > > My question is, if I put my current 50mm on a D7, what would its
> > > equivalent focal length to a 35mm camera be?
> > It'd be equal to a 75mm lens.
> Thanks.
> Does that 1.5 : 1 ratio hold true for all focal lengths? Would my 85 mm
> lens be equivalent to a 127.5 mm lens?

Yes.


Juergen
Anonymous
December 17, 2004 11:12:08 AM

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

In article <41C286C7.CB245732@bigfoot.com>,
"Juergen ." <jaguare@bigfoot.com> wrote:

> > Does that 1.5 : 1 ratio hold true for all focal lengths? Would my
> > 85 mm lens be equivalent to a 127.5 mm lens?
>
> Yes.

Thanks again. I've been using fixed lens digital cameras for years, but
have never had one with interchangeable lenses before.

--
Stop Mad Cowboy Disease: Impeach the son of a Bush.
Anonymous
December 17, 2004 2:07:31 PM

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

Michelle Steiner wrote:

> I currently have a Nikon 35mm SLR, so when I get a digital SLR, it will
> also be a Nikon so I can interchange the lenses between the cameras.
> I'm pretty much settled on the D70.
>
> My question is, if I put my current 50mm on a D7, what would its
> equivalent focal length to a 35mm camera be?

For the D70:

In x the multiplier would be 36mm /23.7mm, or about 1.52.
In y the multiplier would be 24mm /15.5mm, or about 1.55.

Split that and you get 1.53.

Just multiply the FL of the lens by that number to get the 'equivalent'.

50 x 1.53 = 76.5mm
100 x 1.53 = 153mm

and so on.

Cheers,
Alan

--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: there's no such thing as a FreeLunch.
Anonymous
December 18, 2004 12:42:53 AM

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

>> > My question is, if I put my current 50mm on a D7, what would its
>> > equivalent focal length to a 35mm camera be?
>> >
>> It'd be equal to a 75mm lens.
>
>Thanks.
>
>Does that 1.5 : 1 ratio hold true for all focal lengths? Would my 85 mm
>lens be equivalent to a 127.5 mm lens?

Yes, it's always x1.5, but you should also know that a 50mm lens on
your digital Nikon will not behave exactly the same way a 75mm does on
a film camera. The way to think of it is this: you're still shooting
with a 50mm lens, but you're always cropping to end up just using the
middle part of the picture.

-Joel

----------------------------------------------------------------------------
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Anonymous
December 18, 2004 12:42:54 AM

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

In article <xpIwd.3027$4n4.2273@fe11.lga>,
joel@exc.com (Dr. Joel M. Hoffman) wrote:

> Yes, it's always x1.5, but you should also know that a 50mm lens on
> your digital Nikon will not behave exactly the same way a 75mm does
> on a film camera. The way to think of it is this: you're still
> shooting with a 50mm lens, but you're always cropping to end up just
> using the middle part of the picture.

But the cropping is optical, before the image is captured; that's not
the same as cropping with an enlarger (film) or with software (digital).

--
Stop Mad Cowboy Disease: Impeach the son of a Bush.
Anonymous
December 18, 2004 1:38:39 PM

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

Michelle Steiner wrote:
> In article <xpIwd.3027$4n4.2273@fe11.lga>,
> joel@exc.com (Dr. Joel M. Hoffman) wrote:
>
>> Yes, it's always x1.5, but you should also know that a 50mm lens on
>> your digital Nikon will not behave exactly the same way a 75mm does
>> on a film camera. The way to think of it is this: you're still
>> shooting with a 50mm lens, but you're always cropping to end up just
>> using the middle part of the picture.
>
> But the cropping is optical, before the image is captured; that's not
> the same as cropping with an enlarger (film) or with software
> (digital).

Why not?
Anonymous
December 18, 2004 1:38:40 PM

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

In article <32ig4eF3mhh96U1@individual.net>,
"David J Taylor" <david-taylor@invalid.com> wrote:

> > But the cropping is optical, before the image is captured; that's
> > not the same as cropping with an enlarger (film) or with software
> > (digital).
>
> Why not?

Because when you crop the captured image, you're increasing the pixel
size, thus reducing the sharpness.

--
Stop Mad Cowboy Disease: Impeach the son of a Bush.
Anonymous
December 18, 2004 3:38:23 PM

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

Michelle Steiner wrote:
> In article <32ig4eF3mhh96U1@individual.net>,
> "David J Taylor" <david-taylor@invalid.com> wrote:
>
>>> But the cropping is optical, before the image is captured; that's
>>> not the same as cropping with an enlarger (film) or with software
>>> (digital).
>>
>> Why not?
>
> Because when you crop the captured image, you're increasing the pixel
> size, thus reducing the sharpness.

If a CCD sensor is smaller than a full 35mm frome (36 x 24mm), then the
area which the sensor sees is just the same as cropping the 35mm negative
in an enlarger, or cropping a full-frame CCD sensor image in software.

David
Anonymous
December 18, 2004 4:34:13 PM

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

In article <32imm0F3ncbm8U1@individual.net>,
"David J Taylor" <david-taylor@invalid.com> wrote:

> > Because when you crop the captured image, you're increasing the
> > pixel size, thus reducing the sharpness.
>
> If a CCD sensor is smaller than a full 35mm frome (36 x 24mm), then
> the area which the sensor sees is just the same as cropping the 35mm
> negative in an enlarger, or cropping a full-frame CCD sensor image in
> software.

I'm not comparing the same focal length on different sensor or film
sizes; I'm comparing different focal lengths on the same film or sensor
size.

--
Stop Mad Cowboy Disease: Impeach the son of a Bush.
Anonymous
December 18, 2004 4:34:14 PM

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

"Michelle Steiner" <michelle@michelle.org> wrote in message
news:michelle-97EDB1.13341318122004@news.west.cox.net...
> In article <32imm0F3ncbm8U1@individual.net>,
> "David J Taylor" <david-taylor@invalid.com> wrote:
>
> > > Because when you crop the captured image, you're increasing the
> > > pixel size, thus reducing the sharpness.
> >
> > If a CCD sensor is smaller than a full 35mm frome (36 x 24mm), then
> > the area which the sensor sees is just the same as cropping the 35mm
> > negative in an enlarger, or cropping a full-frame CCD sensor image in
> > software.
>
> I'm not comparing the same focal length on different sensor or film
> sizes; I'm comparing different focal lengths on the same film or sensor
> size.

Exactly. Different film and sensor sizes are just that, different. It's
senseless to call it a crop or a magnification.

Greg
Anonymous
December 18, 2004 7:02:46 PM

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

Michelle Steiner wrote:

> I'm not comparing the same focal length on different sensor or film
> sizes; I'm comparing different focal lengths on the same film or sensor
> size.

This sub thread is in a semantic tangle over the word "crop". Don't worry about it.

For the D70 the effective multiplier is approx. 1.53 for every lens FL.

Thus 50mm -> 76.5mm effective. (1.5 is close enough as few lenses stated to be
a specific FL are actually that specific FL ... a couple mm either way is common).

Cheers,
Alan.

--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: there's no such thing as a FreeLunch.
Anonymous
December 18, 2004 7:02:47 PM

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

In article <cq25ti$4m3$1@inews.gazeta.pl>,
Alan Browne <alan.browne@freelunchVideotron.ca> wrote:

> This sub thread is in a semantic tangle over the word "crop". Don't
> worry about it.

Do you mean that I should be anti-semantic?

--
Stop Mad Cowboy Disease: Impeach the son of a Bush.
Anonymous
December 18, 2004 7:21:13 PM

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

G.T. wrote:

>
> Exactly. Different film and sensor sizes are just that, different. It's
> senseless to call it a crop or a magnification.

One way or another, for comparative reasons or anything else, it is useful to
know the 'crop' factor or 'magnification' value between the standard 35mm format
and whatever smaller format digital sensor is used.

Most exp. for those who use the same lens on both film and DSLR's.

Cheers,
Alan.


--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: there's no such thing as a FreeLunch.
Anonymous
December 18, 2004 7:21:14 PM

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

"Alan Browne" <alan.browne@freelunchVideotron.ca> wrote in message
news:cq2705$951$1@inews.gazeta.pl...
> G.T. wrote:
>
> >
> > Exactly. Different film and sensor sizes are just that, different.
It's
> > senseless to call it a crop or a magnification.
>
> One way or another, for comparative reasons or anything else, it is useful
to
> know the 'crop' factor or 'magnification' value between the standard 35mm
format
> and whatever smaller format digital sensor is used.
>

Yes, knowing the conversion factor helps film SLR users pick lenses for
their digital SLRs.

> Most exp. for those who use the same lens on both film and DSLR's.
>

My film SLR experience is limited so the conversion factor is meaningless to
me. To me there is no crop or magnification. I take a picture with my
Digital Rebel and it is what it is.

Greg
Anonymous
December 18, 2004 7:32:19 PM

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

Michelle Steiner wrote:
> In article <cq25ti$4m3$1@inews.gazeta.pl>,
> Alan Browne <alan.browne@freelunchVideotron.ca> wrote:
>
>
>>This sub thread is in a semantic tangle over the word "crop". Don't
>>worry about it.
>
>
> Do you mean that I should be anti-semantic?

As long as you're not anti-semitic.


--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: there's no such thing as a FreeLunch.
Anonymous
December 18, 2004 7:56:42 PM

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

Dr. Joel M. Hoffman wrote:

>>>>My question is, if I put my current 50mm on a D7, what would its
>>>>equivalent focal length to a 35mm camera be?
>>>>
>>>
>>>It'd be equal to a 75mm lens.
>>
>>Thanks.
>>
>>Does that 1.5 : 1 ratio hold true for all focal lengths? Would my 85 mm
>>lens be equivalent to a 127.5 mm lens?
>
>
> Yes, it's always x1.5, but you should also know that a 50mm lens on
> your digital Nikon will not behave exactly the same way a 75mm does on
> a film camera. The way to think of it is this: you're still shooting
> with a 50mm lens, but you're always cropping to end up just using the
> middle part of the picture.

In almost all cases, using a cropped sensor DSLR will use the best part of the
lens where there is the best resolution and the least linear distortion as well
as clearly avoidng vignetting from additional filters such as circ-pols. Given
the overall 'inconvenience' of using 35mm format lenses on cropped DSLR bodies,
these are considerable countervailing benefits.

In most cases, the 'cropped' performance of a specific lens will be better
performance than the 'equivalent FL' lens would be at comparable aperture and price.

A case in point. My 50 f/1.7 will become a 75 (ish) f/1.7. So for US$80 I get
a lens with useability and performance that is close to an 85 f/1.4 which costs
8x as much.

My 300 f/2.8 becomes a 450 f/2.8 or a 630 f/4 with the 1.4TC! Talk about going
up market real fast (with the TC, the res won't be as good as the 600 f/4 of
course, but damned good IAC). With the 2TC, it's a 900 f/5.6!!

My 80-200 goes to 120 - 300 f/8. Great for sports/nature.

In all cases above, of course, the sweetest part of the lens is used.

A minor negative is, that for the narrower FOV of the lens on a cropped sensor,
an excess of glass is presented which increases susceptibility to flare. This
is manageable of course by careful photographers.

Cheers,
Alan.


--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: there's no such thing as a FreeLunch.
Anonymous
December 19, 2004 12:28:45 AM

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

Michelle Steiner <michelle@michelle.org> writes:

> In article <32ig4eF3mhh96U1@individual.net>,
> "David J Taylor" <david-taylor@invalid.com> wrote:
>
> > > But the cropping is optical, before the image is captured; that's
> > > not the same as cropping with an enlarger (film) or with software
> > > (digital).
> >
> > Why not?
>
> Because when you crop the captured image, you're increasing the pixel
> size, thus reducing the sharpness.

"increasing pixel size" ? Not unless you decide to, post-crop, change
the output area over which those pixels are projected.

If you take a CCD which is less than a 35mm frame and print it out at,
say 12"x8", the output projections of those pixels are going to be
larger than if you had the same sized sensor elements spread over a
whole 35mm frame (and thus if you had more of them).

So, in effect, the digital case is identical.

I suggest you try being a little clearer about precisely what you mean
by 'pixel size' because it appears than you're confusing yourself.

B>
Anonymous
December 19, 2004 12:28:46 AM

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

Bruce Murphy wrote:
> Michelle Steiner <michelle@michelle.org> writes:
>
>
>>In article <32ig4eF3mhh96U1@individual.net>,
>> "David J Taylor" <david-taylor@invalid.com> wrote:
>>
>>
>>>>But the cropping is optical, before the image is captured; that's
>>>>not the same as cropping with an enlarger (film) or with software
>>>>(digital).
>>>
>>>Why not?
>>
>>Because when you crop the captured image, you're increasing the pixel
>>size, thus reducing the sharpness.
>
>
> "increasing pixel size" ? Not unless you decide to, post-crop, change
> the output area over which those pixels are projected.
>
> If you take a CCD which is less than a 35mm frame and print it out at,
> say 12"x8", the output projections of those pixels are going to be
> larger than if you had the same sized sensor elements spread over a
> whole 35mm frame (and thus if you had more of them).
>
> So, in effect, the digital case is identical.
>
> I suggest you try being a little clearer about precisely what you mean
> by 'pixel size' because it appears than you're confusing yourself.
>

Relax, Bruce. The OP's original point, lost recently, was that there's a
difference between the cropping that can occur in the *viewfinder* vs.
post production, if you will, cropping. That's true of both pixels and
grains.

--
John McWilliams
Anonymous
December 19, 2004 12:47:40 PM

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

Michelle Steiner wrote:
> In article <32imm0F3ncbm8U1@individual.net>,
> "David J Taylor" <david-taylor@invalid.com> wrote:
>
>>> Because when you crop the captured image, you're increasing the
>>> pixel size, thus reducing the sharpness.
>>
>> If a CCD sensor is smaller than a full 35mm frome (36 x 24mm), then
>> the area which the sensor sees is just the same as cropping the 35mm
>> negative in an enlarger, or cropping a full-frame CCD sensor image in
>> software.
>
> I'm not comparing the same focal length on different sensor or film
> sizes; I'm comparing different focal lengths on the same film or
> sensor size.

OK, I wasn't. To me, crop refers to a cutting of the image, not a change
of focal length.

David
Anonymous
December 19, 2004 12:56:22 PM

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

Alan Browne wrote:
[]
> A case in point. My 50 f/1.7 will become a 75 (ish) f/1.7. So for
> US$80 I get a lens with useability and performance that is close to an
> 85 f/1.4
> which costs 8x as much.
[]
> Cheers,
> Alan.

Not really - you have just the same picture as if you just used the
central part of a full-frame sensor with the 50 f/1.7 lens. By magnifying
and only using the central part you will magnify the any defects as well
(as a fraction of the total image), and make them more visible. Of
course, exactly /how/ visible they are will depend on the lens and sensor.

Cheers,
David
Anonymous
December 19, 2004 2:17:56 PM

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

David J Taylor wrote:

> Alan Browne wrote:
> []
>
>>A case in point. My 50 f/1.7 will become a 75 (ish) f/1.7. So for
>>US$80 I get a lens with useability and performance that is close to an
>>85 f/1.4
>> which costs 8x as much.
>
> []
>
>>Cheers,
>>Alan.
>
>
> Not really - you have just the same picture as if you just used the
> central part of a full-frame sensor with the 50 f/1.7 lens. By magnifying
> and only using the central part you will magnify the any defects as well
> (as a fraction of the total image), and make them more visible. Of
> course, exactly /how/ visible they are will depend on the lens and sensor.

The center of the lens is the least distorted, highest MTF part of the lens, as
any MTF graph will clearly show:
eg: http://www.photodo.com/pix/lens/mtf/MIAF5014.gif
(numbers on the bottom of the graph are radius (mm)from center at the sensor plane)

Cheers,
Alan.

--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: there's no such thing as a FreeLunch.
Anonymous
December 19, 2004 3:14:06 PM

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

Michelle Steiner <michelle@michelle.org> writes:

> In article <32imm0F3ncbm8U1@individual.net>,
> "David J Taylor" <david-taylor@invalid.com> wrote:
>
> > > Because when you crop the captured image, you're increasing the
> > > pixel size, thus reducing the sharpness.
> >
> > If a CCD sensor is smaller than a full 35mm frome (36 x 24mm), then
> > the area which the sensor sees is just the same as cropping the 35mm
> > negative in an enlarger, or cropping a full-frame CCD sensor image in
> > software.
>
> I'm not comparing the same focal length on different sensor or film
> sizes; I'm comparing different focal lengths on the same film or sensor
> size.

Actually, yes you are. The post to which you replied (wrongly) was
comparing 50 and 75mm lenses between film and cropped DSLR bodies. You
appear to be confused enough to start going on about 'optical
cropping'.

B>
Anonymous
December 19, 2004 7:36:46 PM

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

Alan Browne wrote:
[]
>> Not really - you have just the same picture as if you just used the
>> central part of a full-frame sensor with the 50 f/1.7 lens. By
>> magnifying and only using the central part you will magnify the any
>> defects as well (as a fraction of the total image), and make them
>> more visible. Of course, exactly /how/ visible they are will depend
>> on the lens and sensor.
>
> The center of the lens is the least distorted, highest MTF part of
> the lens, as any MTF graph will clearly show:
> eg: http://www.photodo.com/pix/lens/mtf/MIAF5014.gif
> (numbers on the bottom of the graph are radius (mm)from center at the
> sensor plane)
> Cheers,
> Alan.

Agreed, but any defects will still be enlarged as a percentage of the
picture size if the image is cropped.

Cheers,
David
Anonymous
December 19, 2004 8:28:44 PM

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

Alan Browne wrote:
> David J Taylor wrote:
>
>>
>> Agreed, but any defects will still be enlarged as a percentage of the
>> picture size if the image is cropped.
>
> Which defects?

Which ever ones the lens has.

David
Anonymous
December 19, 2004 8:28:45 PM

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

David J Taylor wrote:

> Alan Browne wrote:
>
>>David J Taylor wrote:
>>
>>
>>>Agreed, but any defects will still be enlarged as a percentage of the
>>>picture size if the image is cropped.
>>
>>Which defects?
>
>
> Which ever ones the lens has.

If you can't name them...

Given that the center area of the image is the least affected by distortion and
the most transmissive in MTF, there will be no increase in defects, quite the
opposite... that is to say corner sharpness won't be lost, vignetting will not
occur, distortion will be lesser, not greater.

--
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-- e-meil: there's no such thing as a FreeLunch.
Anonymous
December 19, 2004 11:02:32 PM

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

Alan Browne wrote:
> David J Taylor wrote:
>
>> Alan Browne wrote:
>>
>>> David J Taylor wrote:
>>>
>>>
>>>> Agreed, but any defects will still be enlarged as a percentage of
>>>> the picture size if the image is cropped.
>>>
>>> Which defects?
>>
>>
>> Which ever ones the lens has.
>
> If you can't name them...

No need to name, it applies to /any/ imperfections within the sensitive
area.

> Given that the center area of the image is the least affected by
> distortion and the most transmissive in MTF, there will be no
> increase in defects, quite the opposite... that is to say corner
> sharpness won't be lost, vignetting will not occur, distortion will
> be lesser, not greater.

Of course, I would agree that the general image quality in that region
should be higher than the average for the whole 24 x 36mm image plane.
However, any individual defect will be magnified.

E.g. for a given spatial frequency in the print (as a percentage of the
picture height), the spatial frequency required at the image plane will be
higher. Thus (for typical MTF shapes) the MTF will have to be higher at a
particular spatial frequency to ensure the /same/ MTF at the higher
spatial frequency required by the smaller sensor.

(I feel I've not done a good job of explaining that).

Cheers,
David
Anonymous
December 19, 2004 11:02:33 PM

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

David J Taylor wrote:

> Alan Browne wrote:
>
>>David J Taylor wrote:
>>
>>
>>>Alan Browne wrote:
>>>
>>>
>>>>David J Taylor wrote:
>>>>
>>>>
>>>>
>>>>>Agreed, but any defects will still be enlarged as a percentage of
>>>>>the picture size if the image is cropped.
>>>>
>>>>Which defects?
>>>
>>>
>>>Which ever ones the lens has.
>>
>>If you can't name them...
>
>
> No need to name, it applies to /any/ imperfections within the sensitive
> area.
>
>
>>Given that the center area of the image is the least affected by
>>distortion and the most transmissive in MTF, there will be no
>>increase in defects, quite the opposite... that is to say corner
>>sharpness won't be lost, vignetting will not occur, distortion will
>>be lesser, not greater.
>
>
> Of course, I would agree that the general image quality in that region
> should be higher than the average for the whole 24 x 36mm image plane.
> However, any individual defect will be magnified.
>
> E.g. for a given spatial frequency in the print (as a percentage of the
> picture height), the spatial frequency required at the image plane will be
> higher. Thus (for typical MTF shapes) the MTF will have to be higher at a
> particular spatial frequency to ensure the /same/ MTF at the higher
> spatial frequency required by the smaller sensor.
>
> (I feel I've not done a good job of explaining that).

I know what you're getting at but it's a non-issue as the sensors today cannot
resolve as high as the MTF detail available from the lens. When cropped sensors
for 35mm lenses get to 10 - 15 mpix or so, then that argument will begin to hold.

In short, no reduction in quality, at least that would be visible in a large
print. The benefits outweigh the negatives in this context by a large margin.

I did (in this thread or somewhere else) identify a higher susceptibility to
flare (all that 'unused' front end glass), but the photographer should be able
to manage it if he pays attention to what he's doing.

Cheers,
Alan.


--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
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-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: there's no such thing as a FreeLunch.
Anonymous
December 19, 2004 11:25:20 PM

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

"Ryadia" <ryadia@hotmail.com> writes:

> "David J Taylor" <david-taylor@invalid.com> wrote in message
> news:32l1i7F1a8i0sU1@individual.net...
> >
> > Not really - you have just the same picture as if you just used the
> > central part of a full-frame sensor with the 50 f/1.7 lens. By magnifying
> > and only using the central part you will magnify the any defects as well
> > (as a fraction of the total image), and make them more visible. Of
> > course, exactly /how/ visible they are will depend on the lens and sensor.
> >
> > Cheers,
> > David
> >
> The crop factor is pretty confusing stuff when you are used to a portrait
> lens being 90/100mm. The crop factor of a 50mm lens makes it "look" the same
> size as an 80mm would but with the perspective of a 50mm lens!

No. Perspective is a function of the distance between lens's front
nodal point and the subject. And that's all.

If you crop the image from a 50mm lens to the point where you're getting the
same coverage as 75mm lens, and you are standing in the same place as you
would with a 75mm lens you will get *the identical perspective*.

> It is this
> perspective thing which gives traditional photographers the biggest amount
> of drama. There is not the same opportunity for focus depth with a DSLR
> using a 50mm lens as there is with a 35mm camera using a 90 or 100 mm lens.
> When was the last time you saw a 65mm portrait lens.

Since 50mm lenses tend to be far faster than most portrait lenses, I'd
say that exactly the same opportunities arise. I argee that people
seem to be confused about perspective. You for one.

> I used to pull focus on an eye with f2.0. The cheek or nose would soften and
> conceal skin blemishes. Even at f1.4, a 50mm lens has too much DOF to pull
> this off. I find now that to obtain the same results as I used to get, I
> have to frame a shot using the same lens as I did with film but with greater
> distance between me and the subject.

No, I rather suspect not. the f/1.4 to f/2.0 different should be just edging
on exactly the difference you'd need for your 1.5 crop factor to cancel out
and get exactly the same result.

B>
Anonymous
December 19, 2004 11:25:21 PM

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

Bruce Murphy <pack-news@rattus.net> writes:
> "Ryadia" <ryadia@hotmail.com> writes:
>> "David J Taylor" <david-taylor@invalid.com> wrote:

>>> Not really - you have just the same picture as if you just used
>>> the central part of a full-frame sensor with the 50 f/1.7 lens.
>>> By magnifying and only using the central part you will magnify the
>>> any defects as well (as a fraction of the total image), and make
>>> them more visible. Of course, exactly /how/ visible they are will
>>> depend on the lens and sensor.

>> The crop factor is pretty confusing stuff when you are used to a portrait
>> lens being 90/100mm. The crop factor of a 50mm lens makes it "look" the same
>> size as an 80mm would but with the perspective of a 50mm lens!

> No, I rather suspect not. the f/1.4 to f/2.0 different should be
> just edging on exactly the difference you'd need for your 1.5 crop
> factor to cancel out and get exactly the same result.

Ryadia's 20D has a 1.6 factor, not 1.5. With a 1.6 crop you need to
open up 1 1/3 stop to get the same results. If we do the math, we find
that a 50mm f/1.4 on a 20D becomes the equivalent of a 80 mm f/2.2 on
a film camera. If what you want is 90/100 mm f/2.0, that is too wide
and too slow.

If we do the math for a 1.5 factor (Nikon, Pentax, Fuji, et. al),
we need to open up 1 1/5 stop to get the same results at the same
FOV as film. So a 50mm f/1.4 on a D70 becomes the equivalent of
a 75 mm f/2.1 - and we are still too wide and too slow to match
a 90/100 mm f/2.0.

So what is the "ideal" portrait lens for digital?

I would say that a 60 mm f/1.2 (~ 90 mm f/1.8) would be ideal, - but
that lens doesn't exist. Of those that exist, the Nikkor 85 mm f/1.4
(~ 128 mm f/2.1 is probably one of the better for control over DOF).
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
========================================================================
When you say you live in the real world, which one are you referring to?
Anonymous
December 19, 2004 11:25:22 PM

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

Gisle Hannemyr wrote:
[]
> I would say that a 60 mm f/1.2 (~ 90 mm f/1.8) would be ideal, - but
> that lens doesn't exist. Of those that exist, the Nikkor 85 mm f/1.4
> (~ 128 mm f/2.1 is probably one of the better for control over DOF).

So no modern-day equivalent to the 58mm f/1.2 then?

<http://www.mir.com.my/rb/photography/hardwares/speciall...;

Cheers,
David
Anonymous
December 19, 2004 11:25:22 PM

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

Gisle Hannemyr wrote:

> Bruce Murphy <pack-news@rattus.net> writes:
>
>>"Ryadia" <ryadia@hotmail.com> writes:
>>
>>>"David J Taylor" <david-taylor@invalid.com> wrote:
>
>
>>>>Not really - you have just the same picture as if you just used
>>>>the central part of a full-frame sensor with the 50 f/1.7 lens.
>>>>By magnifying and only using the central part you will magnify the
>>>>any defects as well (as a fraction of the total image), and make
>>>>them more visible. Of course, exactly /how/ visible they are will
>>>>depend on the lens and sensor.
>
>
>>>The crop factor is pretty confusing stuff when you are used to a portrait
>>>lens being 90/100mm. The crop factor of a 50mm lens makes it "look" the same
>>>size as an 80mm would but with the perspective of a 50mm lens!
>
>
>>No, I rather suspect not. the f/1.4 to f/2.0 different should be
>>just edging on exactly the difference you'd need for your 1.5 crop
>>factor to cancel out and get exactly the same result.
>
>
> Ryadia's 20D has a 1.6 factor, not 1.5. With a 1.6 crop you need to
> open up 1 1/3 stop to get the same results. If we do the math, we find
> that a 50mm f/1.4 on a 20D becomes the equivalent of a 80 mm f/2.2 on
> a film camera. If what you want is 90/100 mm f/2.0, that is too wide
> and too slow.

What math are you doing?

Recompute for the DOF "standard" paper size at print (for printed 8x10 at 5 l/mm
or at the extreme 8 l/mm). That is what DOF is all about: perceptible sharp
detail in the printed image. So, given the smaller image area, when it is blown
up to a reference size, the DOF will be shallower as the source image (camera
sensor) is smaller.

Cheers,
Alan


--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: there's no such thing as a FreeLunch.
Anonymous
December 19, 2004 11:25:22 PM

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

Gisle Hannemyr <gisle+njus@ifi.uio.no> wrote:

> So what is the "ideal" portrait lens for digital?

My dream lens is a 50mm f/0.9, designed for top quality wide open (down
to f/2 or so, say), assuming a 1.5 crop factor. I'd pay well for that lens.

--
Jeremy | jeremy@exit109.com
December 19, 2004 11:25:22 PM

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

Gisle Hannemyr <gisle+njus@ifi.uio.no> wrote in
news:q5u0qiqlvc.fsf@viisi.ifi.uio.no:

> I would say that a 60 mm f/1.2 (~ 90 mm f/1.8) would be ideal, - but
> that lens doesn't exist. Of those that exist, the Nikkor 85 mm f/1.4
> (~ 128 mm f/2.1 is probably one of the better for control over DOF).

Surely you mean the Canon 85 f1.2?



--
Mark Heyes (New Zealand)
See my pics at www.gigatech.co.nz (last updated 12-Nov-04)
"There are 10 types of people, those that
understand binary and those that don't"



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Anonymous
December 19, 2004 11:25:23 PM

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

"David J Taylor" <david-taylor@invalid.com> writes:
> Gisle Hannemyr wrote:

>> I would say that a 60 mm f/1.2 (~ 90 mm f/1.8) would be ideal, - but
>> that lens doesn't exist. Of those that exist, the Nikkor 85 mm f/1.4
>> (~ 128 mm f/2.1 is probably one of the better for control over DOF).
>
> So no modern-day equivalent to the 58mm f/1.2 then?
> <http://www.mir.com.my/rb/photography/hardwares/speciall...;

I didn't now about that one - thanks for the link!

Discontinued in 1997 - according to another page I found when
googling for more info. Let's hope Nikon resurrect it.
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
========================================================================
When you say you live in the real world, which one are you referring to?
Anonymous
December 19, 2004 11:25:23 PM

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

Alan Browne <alan.browne@freelunchVideotron.ca> writes:
> What math are you doing?

I math I learnt when taking phitography classes in college.
This is the textbook I use: Allen R. Greenleaf: Photographic
Optics, MacMillan.

> Recompute for the DOF "standard" paper size at print (for printed 8x10
> at 5 l/mm or at the extreme 8 l/mm). That is what DOF is all about:
> perceptible sharp detail in the printed image.

No argument from here - DOF is clearly a perceptible quality.

> So, given the smaller image area, when it is blown up to a reference
> size, the DOF will be shallower as the source image (camera sensor)
> is smaller.

This is too simplistic.

Your statement is correct if - and only if - the focal length stays
the same when we move between formats. If we change to a wider focal
length to maintain FOV - and that is exactly what people that do - DOF
will be /deeper/.

This is obvious from the first graph on this webpage:

http://heim.ifi.uio.no/~gisle/photo/dof.html

A smaller sensor requires a shorter focal length to maintain FOV,
and that results in a /deeper/ DOF.

In case you don't trust my math, it is also a demonstrable fact, as
evident from this page (by Todd Walker):

http://www.toddwalker.net/doftest/

Walker's webpage shows two near identical shots taken with the same
FOV and same aperture with a Canon G1 (4.8x crop) and a Canon 10D
(1.6x crop). It is pretty obvious that the DOF of the camera with the
smaller sensor is deeper - not smaller as you seem to think.

For good measure, graph 2 on the same page show that if we keep the
focal length constant, if you travel along the Z-axis, DOF decreases
when we move to smaller sensor diameters. That is caused by the
magnification to a reference size you are talking about - but its
effect is «overshadowed» by the effect of changing focal length.
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
========================================================================
When you say you live in the real world, which one are you referring to?
Anonymous
December 19, 2004 11:25:23 PM

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

Alan Browne <alan.browne@freelunchVideotron.ca> writes:
> What math are you doing?

I math I picked up when taking photography classes in college.
(From this textbook: Allen R. Greenleaf: Photographic Optics,
MacMillan.)

> Recompute for the DOF "standard" paper size at print (for printed 8x10
> at 5 l/mm or at the extreme 8 l/mm).

What has l/mm and printing to do with DOF? Are you confusing
resolution with depth of field?

> That is what DOF is all about: perceptible sharp detail in the
> printed image.

No argument from me - yes, DOF is a perceptible quality.

> So, given the smaller image area, when it is blown up to a reference
> size, the DOF will be shallower as the source image (camera sensor)
> is smaller.

This is too simplistic.

Your statement is correct if - and only if - the focal length stays
the same when we move between formats. If we change to a wider focal
length to maintain FOV - and that is exactly what photographer's do -
DOF will be /deeper/.

The first graph on this webpage shows the DOF as a function of
sensor size/focal length, keeping the FOV constant:

http://heim.ifi.uio.no/~gisle/photo/dof.html

A smaller sensor requires a shorter focal length to maintain FOV.
That results in a /deeper/ DOF, not shallower as you seem to think.

And in case you don't trust my math, it is also a demonstrable fact,
as evident from this webpage (by Todd Walker):

http://www.toddwalker.net/doftest/

Walker's webpage shows two near identical shots taken with the same
FOV and same aperture with a Canon G1 (4.8x crop) and a Canon 10D
(1.6x crop).
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
========================================================================
When you say you live in the real world, which one are you referring to?
Anonymous
December 19, 2004 11:25:24 PM

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

Gisle Hannemyr wrote:

> Alan Browne <alan.browne@freelunchVideotron.ca> writes:
>
>>What math are you doing?
>
>
> I math I picked up when taking photography classes in college.
> (From this textbook: Allen R. Greenleaf: Photographic Optics,
> MacMillan.)
>
>
>>Recompute for the DOF "standard" paper size at print (for printed 8x10
>>at 5 l/mm or at the extreme 8 l/mm).
>
>
> What has l/mm and printing to do with DOF? Are you confusing
> resolution with depth of field?

Printing is what DOF is all about. The DOF markings on your lens trace through
reproduction from the negative to an 8x10 print.


>
>
> This is too simplistic.

It is what DOF markings on lenses refer to, it is what programs such as fcalc
compute to (or really where they get the CoC number).

> Your statement is correct if - and only if - the focal length stays
> the same when we move between formats. If we change to a wider focal
> length to maintain FOV - and that is exactly what photographer's do -
> DOF will be /deeper/.

Print an image smaller and it looks sharper and to have deeper DOF as a
consequence. The OOF blur is compressed making it appear to have more DOF than
at the reference size of 8x10.

Refer to:

http://www.nikonlinks.com/unklbil/dof.htm

Cheers,
Alan.


--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
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-- e-meil: there's no such thing as a FreeLunch.
Anonymous
December 20, 2004 12:04:38 AM

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

"David J Taylor" <david-taylor@invalid.com> wrote in message
news:32l1i7F1a8i0sU1@individual.net...
>
> Not really - you have just the same picture as if you just used the
> central part of a full-frame sensor with the 50 f/1.7 lens. By magnifying
> and only using the central part you will magnify the any defects as well
> (as a fraction of the total image), and make them more visible. Of
> course, exactly /how/ visible they are will depend on the lens and sensor.
>
> Cheers,
> David
>
The crop factor is pretty confusing stuff when you are used to a portrait
lens being 90/100mm. The crop factor of a 50mm lens makes it "look" the same
size as an 80mm would but with the perspective of a 50mm lens! It is this
perspective thing which gives traditional photographers the biggest amount
of drama. There is not the same opportunity for focus depth with a DSLR
using a 50mm lens as there is with a 35mm camera using a 90 or 100 mm lens.
When was the last time you saw a 65mm portrait lens?

I used to pull focus on an eye with f2.0. The cheek or nose would soften and
conceal skin blemishes. Even at f1.4, a 50mm lens has too much DOF to pull
this off. I find now that to obtain the same results as I used to get, I
have to frame a shot using the same lens as I did with film but with greater
distance between me and the subject.

Doug
Anonymous
December 20, 2004 12:04:39 AM

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

Ryadia wrote:
[]
> The crop factor is pretty confusing stuff when you are used to a
> portrait lens being 90/100mm. The crop factor of a 50mm lens makes it
> "look" the same size as an 80mm would but with the perspective of a
> 50mm lens! It is this perspective thing which gives traditional
> photographers the biggest amount of drama. There is not the same
> opportunity for focus depth with a DSLR using a 50mm lens as there is
> with a 35mm camera using a 90 or 100 mm lens. When was the last time
> you saw a 65mm portrait lens?
>
> I used to pull focus on an eye with f2.0. The cheek or nose would
> soften and conceal skin blemishes. Even at f1.4, a 50mm lens has too
> much DOF to pull this off. I find now that to obtain the same results
> as I used to get, I have to frame a shot using the same lens as I did
> with film but with greater distance between me and the subject.
>
> Doug

Interesting, Doug. So for portraits....

- you want the same perspective as a 90mm lens (say), so that defines your
viewpoint.

- you now want the same FOV, so that defines the new focal length required
as 1.5 x 90mm, i.e. 60mm.

- you want the same DOF as your 90mm f/2.0, so you need an aperture of
what? f/1.3? (I'm unsure about this).

- so you need a 60mm f/1.3 lens on digital (crop) to get the same results
as you 90mm f/2.0 on film?

Back of the envelope agrees with what you say....

What are the implications of going the other way? Is 6 x 6cm an "easier"
format for portraiture?

Cheers,
David
Anonymous
December 20, 2004 12:04:39 AM

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

Ryadia wrote:

> "David J Taylor" <david-taylor@invalid.com> wrote in message
> news:32l1i7F1a8i0sU1@individual.net...
>
>>Not really - you have just the same picture as if you just used the
>>central part of a full-frame sensor with the 50 f/1.7 lens. By magnifying
>>and only using the central part you will magnify the any defects as well
>>(as a fraction of the total image), and make them more visible. Of
>>course, exactly /how/ visible they are will depend on the lens and sensor.
>>
>>Cheers,
>>David
>>
>
> The crop factor is pretty confusing stuff when you are used to a portrait
> lens being 90/100mm. The crop factor of a 50mm lens makes it "look" the same
> size as an 80mm would but with the perspective of a 50mm lens! It is this

Perspective is independant of focal length. The perspective to a subject with a
600mm lens at a given point is the same as a 20mm lens at that point. The
difference is field of view.

> perspective thing which gives traditional photographers the biggest amount
> of drama. There is not the same opportunity for focus depth with a DSLR
> using a 50mm lens as there is with a 35mm camera using a 90 or 100 mm lens.
> When was the last time you saw a 65mm portrait lens?

The field of view of a 50mm lens on a 1.5 cropped sensor is identical to the FOV
on a 75mm lens (if such a lens existed.)

Cheers,
Alan


--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
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-- e-meil: there's no such thing as a FreeLunch.
Anonymous
December 20, 2004 12:04:39 AM

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

Ryadia wrote:

> The crop factor is pretty confusing stuff when you are used to a
> portrait lens being 90/100mm. The crop factor of a 50mm lens makes
> it "look" the same size as an 80mm would but with the perspective
> of a 50mm lens! It is this perspective thing which gives
> traditional photographers the biggest amount of drama.

Hmmm... perspective does not change when you crop or change focal
length. As long as the photographer is at the same vantage point with
respect to the scene - perspective is not affected by focal length or
by cropping. Moving closer or further away changes perspective.

Something change, but not perspective. Maybe you are talking about
the combination of "FOV" (field of view) and "DOF" (depth of field)?
I agree that both those things change when you go from film to the
sub-APC-C sensor of a DSLR - I am just not comfortable with calling
it "perspective". Oh, well - let's not get stuck on semantics.

> There is not the same opportunity for focus depth with a DSLR using
> a 50mm lens as there is with a 35mm camera using a 90 or 100 mm
> lens. When was the last time you saw a 65mm portrait lens?

True. In principle you should adjust the focal length by 63 % to
compensate for the crop factor and open up the aperture 1 1/3 stops
more to compensate for the increased DOF of the wider focal length.
If my math is correct, that will give you exactly the same FOV/DOF on
a 20D as you used to get with film.

However, /finding/ a lens with 63 % of the focal length a 1 1/3 wider
maximum aperture is not an easy task. If it exists at all, it is
bound to be expensive.

> I used to pull focus on an eye with f2.0. The cheek or nose would
> soften and conceal skin blemishes. Even at f1.4, a 50mm lens has
> too much DOF to pull this off. I find now that to obtain the same
> results as I used to get, I have to frame a shot using the same
> lens as I did with film but with greater distance between me and
> the subject.

That is probably the cheapest and most practical solution to a shallow
enough DOF on a smaller sensor. But if you move back to get the same
FOV as with film, then the perspective changes.

As for your 50 mm f/1.4, it will (on a EOS 20D) FOV/DOF as an
80 mm f/2.2 on 35 mm film body - and that doesn't cut it (my
favourite portrait lens in my film days was a Nikkor 85mm f/1.8).

To have the equivalent FOV/DOF of 90mm f/2.0 on film, you
need to stick a 56.25 mm f/1.25 on a 20D.
IFAIK, no such animal exists - so moving back is probably the
only practical option.
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
========================================================================
When you say you live in the real world, which one are you referring to?
Anonymous
December 20, 2004 12:04:39 AM

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

Ryadia <ryadia@hotmail.com> wrote:

> The crop factor is pretty confusing stuff when you are used to a portrait
> lens being 90/100mm. The crop factor of a 50mm lens makes it "look" the same
> size as an 80mm would but with the perspective of a 50mm lens!

A 50mm lens doesn't have a perspective.

If you shoot with a 50mm lens from the same distance you would have used a
75mm lens from on a 35mm camera, you'll get the same perspective in both
cases. The depth of field will be slightly greater, however, so you'll
need to open up a little bit to compensate for that.

--
Jeremy | jeremy@exit109.com
Anonymous
December 20, 2004 12:04:40 AM

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

David J Taylor wrote:
[]
> - you now want the same FOV, so that defines the new focal length
> required as 1.5 x 90mm, i.e. 60mm.

Corrected 90mm / 1.5 = 60mm

David
Anonymous
December 20, 2004 12:04:40 AM

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

Ryadia wrote:

> The crop factor is pretty confusing stuff when you are used to a
> portrait lens being 90/100mm. The crop factor of a 50mm lens makes
> it "look" the same size as an 80mm would but with the perspective
> of a 50mm lens! It is this perspective thing which gives
> traditional photographers the biggest amount of drama.

Hmmm... perspective does not change when you crop or change focal
length. As long as the photographer is at the same vantage point with
respect to the scene - perspective is not affected by focal length or
by cropping. Moving closer or further away changes perspective.

Something change, but not perspective. Maybe you are talking about
the combination of "FOV" (field of view) and "DOF" (depth of field)?
I agree that both those things change when you go from film to a the
sub-APC-C sensor of DSLR - I am just comfortable with calling it
"perspective". Oh, well - let's not get stuck on semantics.

> There is not the same opportunity for focus depth with a DSLR using
> a 50mm lens as there is with a 35mm camera using a 90 or 100 mm
> lens. When was the last time you saw a 65mm portrait lens?

True. In principle you should adjust the focal length by 63 % to
compensate for the crop factor and open up the aperture 1 1/3 stops
more to compensate for the increased DOF of the wider focal length.
If my math is correct, that will give you exactly the same FOV/DOF on
a 20D as you used to get with film.

However, /finding/ a lens with 63 % of the focal length a 1 1/3 wider
maximum aperture is not an easy task. If it exists at all, it is
bound to be expensive.

> I used to pull focus on an eye with f2.0. The cheek or nose would
> soften and conceal skin blemishes. Even at f1.4, a 50mm lens has
> too much DOF to pull this off. I find now that to obtain the same
> results as I used to get, I have to frame a shot using the same
> lens as I did with film but with greater distance between me and
> the subject.

That is probably the cheapest and most practical solution to a shallow
enough DOF on a smaller sensor. But if you move back to get the same
FOV as with film, then the perspective changes.

As for your 50 mm f/1.4, it will (on a EOS 20D) FOV/DOF as an
80 mm f/2.2 on 35 mm film body - and that doesn't cut it (my
favourite portrait lens in my film days was a Nikkor 85mm f/1.8).

To have the equivalent FOV/DOF of 90mm f/2.0 on film, you
need to stick a 56.25 mm f/1.25 on a 20D.
IFAIK, no such animal exists - so moving back is probably the
only option.
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
========================================================================
When you say you live in the real world, which one are you referring to?
Anonymous
December 20, 2004 3:16:07 AM

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

Alan Browne <alan.browne@freelunchVideotron.ca> writes:
> Gisle Hannemyr wrote:
>> Alan Browne <alan.browne@freelunchVideotron.ca> writes:

>>>What math are you doing?

>> The math I picked up when taking photography classes in college.
>> (From this textbook: Allen R. Greenleaf: Photographic Optics,
>> MacMillan.)
>> And in case you don't trust my math, it is also a demonstrable fact,
>> as evident from this webpage (by Todd Walker):
>> http://www.toddwalker.net/doftest/

> Refer to:
> http://www.nikonlinks.com/unklbil/dof.htm

OK - you've found a confused guy with a webpage - and you prefer that
to math derived from a classic textbook on Photographic Optics, along
with photographic evidence that confirm what the math predicts.

Suit you.
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
========================================================================
When you say you live in the real world, which one are you referring to?
!