Digital 17mm Is Not Equivelent 27mm on 35mm Film

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bob <Jwx1.nothing@bellsouth.net> wrote:
>
> QUOTE:
>> If you shoot tall buildings at 17mm on digital (with 1.6 crop
>> factor), you still get distorted pics just like 17mm lenses
>> on 35mm film cameras.
>
> Sounds like a complaint about barrel distortion to me.

Every digicam and DSLR test I have seen so far
shows some kind of barrel distortion, usually much worse than moderate,
often objectionable, at wide angle.

This is even true of overpriced lenses like the Nikon 17-55/2.8 DX.

 

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"David J. Littleboy" <davidjl@gol.com> wrote in message
news:cq7k3i$mqh$1@nnrp.gol.com...
SNIP
> Thinking of it as a "crop factor" is what caused both the original
> poster's error and the common error in which people think the
> DOF stays the same for the same lens. That's because it focuses
> people's minds on a given lens being used on both cameras and
> not realizing that the same lens is functions differently on the
> different cameras.

True, but that's only because DOF is a function of output
size/magnification as well, which has little to do with perspective
(depending on how the other variables are chosen).

> The best term would be "format conversion factor", since that's
> what it is. That would make people realize that the 1.6x cameras
> are a different format from 35mm and allow them to think about the
> different photographic functions of a given lens on the different
> formats.

I agree, but it would probably result in even longer threads... ;-(

Bart

 

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"DSphotog" <dsmith5knot@optonline.net> wrote:

> The "big nose" effect is due to camera position.

Exactly!

> Therefore given the same
> cropping (image size) of the person and 50mm lens on a 1.5 factor digital
> camera would give the perspective of a 75mm lens on a 35mm camera. (same
> distance from subject for same image size as the 75 lens on 35mm camera) A
> digital with a 1.6 factor would yield an 80mm perspective. This is all
based
> on camera distance to subject.

Still spot on, but:

> Longer lenses flatten perspective thus
> allowing nose and ears to appear more correct in their relationship to
each
> other. (Hope I didn't jumble that too badly)

And I hope you don't mind the following quibble<g>.

The longer lens does not "flatten perspective": it provides magnification
(relative to a shorter lens) so that you can achieve the framing you want at
a (longer) distance such that the perspective is "flatter".

David J. Littleboy
Tokyo, Japan

 

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David,

Quibble read, digested and accepted. Even though American English is my
first language sometimes it just doesn't seem that way.

Best,
Dave