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Optical difference between film SLRs and DSLRs?

 
 
223rem
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      11-17-2005
Is it only the size of the sensor? In other words, if I use
the same lens (say 50mm), focused the same way, on a film
SLR and on a DSLR, both cameras viewing the same scene from the
same vantage point, then the image taken by the DSLR will simply
be a cropped version of the image taken by the film SLR? That is,
if I cut off the borders of film photograph I will obtain the
image taken by the DSLR?

Thanks.
 
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Lorem Ipsum
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      11-17-2005
"223rem" <(E-Mail Removed)> wrote in message
news:EB5ff.547225$x96.357169@attbi_s72...
> Is it only the size of the sensor?


For all practical purposes, Yes.


 
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John Bean
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      11-17-2005
On Thu, 17 Nov 2005 20:19:48 GMT, 223rem
<(E-Mail Removed)> wrote:

>That is,
>if I cut off the borders of film photograph I will obtain the
>image taken by the DSLR?


Exactly so. If only everybody could get it into their heads
that it's a *crop*, not a change of focal length.

--
John Bean
 
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John A. Stovall
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      11-17-2005
On Thu, 17 Nov 2005 20:19:48 GMT, 223rem <(E-Mail Removed)> wrote:

>Is it only the size of the sensor? In other words, if I use
>the same lens (say 50mm), focused the same way, on a film
>SLR and on a DSLR, both cameras viewing the same scene from the
>same vantage point, then the image taken by the DSLR will simply
>be a cropped version of the image taken by the film SLR? That is,
>if I cut off the borders of film photograph I will obtain the
>image taken by the DSLR?


Not if you use a full frame DSLR such as a Canon 1DsMkII or 5D.


************************************************** ****

"I have been a witness, and these pictures are
my testimony. The events I have recorded should
not be forgotten and must not be repeated."

-James Nachtwey-
http://www.jamesnachtwey.com/
 
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Charlie Ih
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      11-17-2005
In article <(E-Mail Removed)>,
John Bean <(E-Mail Removed)> wrote:
>On Thu, 17 Nov 2005 20:19:48 GMT, 223rem
><(E-Mail Removed)> wrote:
>
>>That is,
>>if I cut off the borders of film photograph I will obtain the
>>image taken by the DSLR?

>
>Exactly so. If only everybody could get it into their heads
>that it's a *crop*, not a change of focal length.
>


Physically the focal length has not changed and the fact is that the
image is cropped". However, in digital photography, we no longer
have a "standard" 36 x 24 format. To make things more easy to understand,
we now use the 35 mm equivalent focal length w.r.t. image angular coverage.
The sensor size (diagonal) of many of the DSLR is 1.5x (or 1.6x) smaller than
that of a film SLR, therefore the 35 mm equivalent focal length of
DSLR is 1.5x (or 1.6x) longer.

BTW, the diagonal of 36 x 24 mm is 43 mm and that of 36 x 36 mm is
50.9 (or 51 or 52). The accepted standard normal lens of 50 mm is by
"accident". Many very old SLR had 43 mm and/or 52 mm "Normal" lens.

 
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223rem
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      11-17-2005
Charlie Ih wrote:

> 50.9 (or 51 or 52). The accepted standard normal lens of 50 mm is by
> "accident". Many very old SLR had 43 mm and/or 52 mm "Normal" lens.


I thought that the normal lens is defined by the fact that, if you
look through the viewfinder of a SLR fitted with such a lens,
the apparent size of objects is same as seen with the naked eye.
Indeed, if you look at a scene with one eye through a viewfinder at
50 mm and the other eye "naked", you have no trouble fusing the two images.
 
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John Bean
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      11-17-2005
On Thu, 17 Nov 2005 21:33:37 GMT, 223rem
<(E-Mail Removed)> wrote:

>Charlie Ih wrote:
>
>> 50.9 (or 51 or 52). The accepted standard normal lens of 50 mm is by
>> "accident". Many very old SLR had 43 mm and/or 52 mm "Normal" lens.

>
>I thought that the normal lens is defined by the fact that, if you
>look through the viewfinder of a SLR fitted with such a lens,
>the apparent size of objects is same as seen with the naked eye.
>Indeed, if you look at a scene with one eye through a viewfinder at
>50 mm and the other eye "naked", you have no trouble fusing the two images.


No, that depends on the magnification of the finder as well
as the focal length of the lens. The "standard" is usually
defined as the diagonal of the image frame, which is about
43mm for a 24x36mm frame.

--
John Bean
 
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Lorem Ipsum
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      11-17-2005
"223rem" <(E-Mail Removed)> wrote in message
news:RG6ff.547297$x96.44831@attbi_s72...
> Charlie Ih wrote:
>
>> 50.9 (or 51 or 52). The accepted standard normal lens of 50 mm is by
>> "accident". Many very old SLR had 43 mm and/or 52 mm "Normal" lens.

>
> I thought that the normal lens is defined by the fact that, if you
> look through the viewfinder of a SLR fitted with such a lens,
> the apparent size of objects is same as seen with the naked eye.
> Indeed, if you look at a scene with one eye through a viewfinder at
> 50 mm and the other eye "naked", you have no trouble fusing the two
> images.


Nope. That is not how 'normal' is defined, and there's a good reason:
viewfinder images differ. A perfect 1:1 would be as you describe: with one
eye open and the other in the viewfinder, the scene would look 'normal' -
same size image. It rarely works out that way. (One obsolete perfect example
is Nikon F with F screen under their 'sports finder' with their 85mm lens.)

Normal is usually calculated as the diagonal of the _format_ (sensor,
exposed film area). (For purposes of numerical comparisons of perspectives
between formats, sometimes the long side is used for both dimensions in the
calculation.)


 
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223rem
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      11-17-2005
Lorem Ipsum wrote:
> "223rem" <(E-Mail Removed)> wrote in message
> news:RG6ff.547297$x96.44831@attbi_s72...
>
>>Charlie Ih wrote:
>>
>>
>>>50.9 (or 51 or 52). The accepted standard normal lens of 50 mm is by
>>>"accident". Many very old SLR had 43 mm and/or 52 mm "Normal" lens.

>>
>>I thought that the normal lens is defined by the fact that, if you
>>look through the viewfinder of a SLR fitted with such a lens,
>>the apparent size of objects is same as seen with the naked eye.
>>Indeed, if you look at a scene with one eye through a viewfinder at
>>50 mm and the other eye "naked", you have no trouble fusing the two
>>images.

>
>
> Nope. That is not how 'normal' is defined, and there's a good reason:
> viewfinder images differ. A perfect 1:1 would be as you describe: with one
> eye open and the other in the viewfinder, the scene would look 'normal' -
> same size image. It rarely works out that way. (One obsolete perfect example
> is Nikon F with F screen under their 'sports finder' with their 85mm lens.)
>
> Normal is usually calculated as the diagonal of the _format_ (sensor,
> exposed film area). (For purposes of numerical comparisons of perspectives
> between formats, sometimes the long side is used for both dimensions in the
> calculation.)


But surely it is not a coincidence that around 50 mm, with a 'normal'
viewfinder, images tend to be as I described.

 
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Skip M
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      11-17-2005
"223rem" <(E-Mail Removed)> wrote in message
news:EB5ff.547225$x96.357169@attbi_s72...
> Is it only the size of the sensor? In other words, if I use
> the same lens (say 50mm), focused the same way, on a film
> SLR and on a DSLR, both cameras viewing the same scene from the
> same vantage point, then the image taken by the DSLR will simply
> be a cropped version of the image taken by the film SLR? That is,
> if I cut off the borders of film photograph I will obtain the
> image taken by the DSLR?
>
> Thanks.


Well, yes, on most digital SLRs. But there are two exceptions, both
relatively expensive, the Canon 5D ($3300) and the Canon 1Ds mkII ($7000).
Both use sensors that are effectively the same dimensions as a frame of 35mm
film, referred to as "full frame." The Kodak DC/n (Nikon lens mount) and
DC/c (Canon lens mount) used a "full frame sensor, too, but they're out of
production.

--
Skip Middleton
http://www.shadowcatcherimagery.com


 
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