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OK you pedants - what is the *exact* size of a 35mm image?

 
 
Alan F Cross
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      08-03-2003
So the 10D has a "magnification ratio of lens focal length of 1.6
compared with 35mm usage. Then a pedant comes along and says it's 1.58,
another says it's 1.59.

I know this is purely academic (if you're bored, quit now!), but what
are the *exact* dimensions of a 35mm image? Most of us say it's 36mm x
24mm, but perhaps this is only an approximation. Anyone accurately
calculating a dSLR 'ratio' from its sensor size needs to know exactly
what size a 35mm image should be.

Now, no guessing, no assumptions, who can point me at an authority where
the precise 35mm size is recorded?
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Phil Stripling
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      08-03-2003
Alan F Cross <(E-Mail Removed)> writes:

> I know this is purely academic (if you're bored, quit now!), but what
> are the *exact* dimensions of a 35mm image? Most of us say it's 36mm x
> 24mm, but perhaps this is only an approximation. Anyone accurately
> calculating a dSLR 'ratio' from its sensor size needs to know exactly
> what size a 35mm image should be.


See the following ANSI standards:
ANSI PH7.1-1971
ANSI PH3.41-1972(R1991)
ANSI PH3.43-1969
ANSI Y15.1-1959

See the following URLs:
http://www.imagingspectrum.com/cgi-l...html?E+scstore
http://digilander.libero.it/comolli/resol2.htm
http://www.panoguide.com/technique/digitising.html
http://www.photo.net/bboard/q-and-a-...?msg_id=005HBS
http://www.earthboundlight.com/phototips/20021215.html


(Watch for wrapping on that first one.)
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Jim Townsend
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      08-03-2003
Alan F Cross wrote:

> So the 10D has a "magnification ratio of lens focal length of 1.6
> compared with 35mm usage. Then a pedant comes along and says it's 1.58,
> another says it's 1.59.
>
> I know this is purely academic (if you're bored, quit now!), but what
> are the *exact* dimensions of a 35mm image? Most of us say it's 36mm x
> 24mm, but perhaps this is only an approximation. Anyone accurately
> calculating a dSLR 'ratio' from its sensor size needs to know exactly
> what size a 35mm image should be.
>
> Now, no guessing, no assumptions, who can point me at an authority where
> the precise 35mm size is recorded?



All I've read shows the 35mm frame is 36mm wide. The 10D sensor is 22.7mm
wide.

So 36 / 22.7 = 1.585903083

1.6 is so much easier to work with


 
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Alan F Cross
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      08-03-2003
In message <(E-Mail Removed)>, Phil Stripling
<(E-Mail Removed)> writes
>Alan F Cross <(E-Mail Removed)> writes:
>
>> I know this is purely academic (if you're bored, quit now!), but what
>> are the *exact* dimensions of a 35mm image? Most of us say it's 36mm x
>> 24mm, but perhaps this is only an approximation. Anyone accurately
>> calculating a dSLR 'ratio' from its sensor size needs to know exactly
>> what size a 35mm image should be.

>
>See the following ANSI standards:
>ANSI PH7.1-1971
>ANSI PH3.41-1972(R1991)
>ANSI PH3.43-1969
>ANSI Y15.1-1959
>
>See the following URLs:
>http://www.imagingspectrum.com/cgi-l...n_eos_1ds_digi
>tal_camera.html?E+scstore
>http://digilander.libero.it/comolli/resol2.htm
>http://www.panoguide.com/technique/digitising.html
>http://www.photo.net/bboard/q-and-a-...?msg_id=005HBS
>http://www.earthboundlight.com/phototips/20021215.html
>

Interestingly, the first link above has the following statements in
respect of the Canon 1Ds

"an imaging area of 24 x 36mm, the same dimensions used by full-frame
35mm SLRs"

"Image size: 35.8 x 23.8mm (1.4 x 1 in)"

By deduction 4064 sensors at 8.8um comes to 35.7632 mm

I suspect there's rounding off in some of these figures, so the question
remains. Is the 1Ds *exactly* the same as 35mm film, or is film
*exactly* 36mm x 24mm?

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Alan F Cross
 
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Larry Caldwell
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      08-03-2003
http://www.velocityreviews.com/forums/(E-Mail Removed) (David J Taylor) writes:

> I bet that 35mm film is exactly 36 x 24mm, but that most manufacturers
> will make their image area slightly smaller to allow for subsequent
> processing. In the case of professional cameras, perhaps not smaller at
> all.


The real nuisance is that manufacturers make their viewfinder image
smaller than full frame, and photo processors typically print at less
than full frame. You pretty much have to do your own darkroom work to
get a full frame print.


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JPS@no.komm
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      08-05-2003
In message <(E-Mail Removed)>,
Jim Townsend <(E-Mail Removed)> wrote:

>All I've read shows the 35mm frame is 36mm wide. The 10D sensor is 22.7mm
>wide.
>
>So 36 / 22.7 = 1.585903083
>
>1.6 is so much easier to work with


Most converters ignore 12 horizontal pixels, and 8 vertical pixels, so
it may actually be closer to 1.6 with a 3072*2048 image (the sensor
actually records 3084*2056).
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