Archived posting to the Leica Users Group, 2001/02/07

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Subject: Re: [Leica] RE: DOF
From: John Collier <jbcollier@home.com>
Date: Wed, 07 Feb 2001 11:28:52 -0700

DOF tables commonly relate the perceived DOF to a standard PRINTED image
size. They also assume that if you expose all of a negative then perhaps you
might be interested in making use of as much of it as you can. If all we
view are contact prints, you and Austin are completely correct. However, it
is not common practice up here for clients to request contact prints.
Perhaps customs differ elsewhere. Clients request a specific output to suit
their needs and are not concerned with the input size at all, provided the
quality is there.

For example, one might get a request for several 8x10s. Now one could use an
8x10 view camera and supply the customer what he wants but if I submit a
35mm contact print telling him that this is what he should want, they may
not agree.

John Collier

Who is genuinely puzzled that this seems to be a difficult subject. I cannot
imagine any simpler way to explain it. DOF tables naturally have to refer to
a specific printed image size or else what practical use could they be? Who
cares how sharp a 35mm contact print looks if you need a x by y?

> From: Jim Brick <jim_brick@agilent.com>
> 
> If the "image size" on the film is the same, the DOF is the same for a
> given f/stop, REGARDLESS OF FOCAL LENGTH and REGARDLESS OF THE FILM SIZE.
> 
> This is a simple fact.