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[OM] Re: Figuring out depth of field with 4/3 adaptor

Subject: [OM] Re: Figuring out depth of field with 4/3 adaptor
From: "Michael R. Collins" <michael789@xxxxxxxxxxxx>
Date: Sun, 27 Mar 2005 15:03:31 -0500
>...A 24mm lens ... always and forever projects the same image out 
>its behind relative to the scene in front of it, meaning, assuming 
>the lens-to-film (or sensor) distance is correct, even the 
>foot/meter distance scale will be correct, and, obviously, the COC, 
>DOF and FOV will be the same.

Walt, this is where you lose me. No question the *projected* image at 
the sensor, whether it's 35mm film or 110 film or 8x10 film or small 
or large digital sensor, will have the same "sharpness" in that plane 
regardless of the sensor type or size. However, I have always 
understood DoF to be dependent not only on the lens but also the 
format - 35mm, MF, LF... (and also on assumptions made about viewing 
distance and quality of eyesight, but factor those out for now). For 
any given format, you use a factor (e.g., typically 5x for 35mm, less 
for MF and even less for LF) to account for a *viewed* image as 
opposed to the image projected on the sensor.

The answer to the "digital DoF" question, then, would depend on the 
factor used, and is the same as for 35mm only if the factor is the 
same, which I doubt. I'm off to search the literature; no idea 
whether I'll find anything.

There's a further issue of CoC vs. pixel size, which can be left for 
the next discussion :-) .

Michael
-- 
Michael R. Collins  ...  Michael.Collins@xxxxxxxxxxxxxxx
Toronto, Ontario, Canada

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