Archived posting to the Leica Users Group, 2001/02/08

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Subject: Re: [Leica] Re: DOF -Optical vs Apparent
From: John Collier <>
Date: Thu, 08 Feb 2001 07:28:23 -0700

If this is your definition of optical depth of field versus apparent depth
of field, you are incorrect. There is only a plane of focus, it has no
width. Any observable width is an optical illusion involving varying sizes
of COC and the image size you choose to observe; that is, in photographic
terms, contact, reduction or enlargement.

If we are discussing this "optical depth of field" then I agree, negative
size, lens focal length and focused distance has no effect. It is always a
plane having no width. Naturally you do not need a DOF table to calculate
this. You use a DOF table to calculate what the depth of focus our brains
are fooled into seeing. A DOF table has to calculated using a fixed COC, a
fixed output (whether that involves enlargement, reduction or contacting the
negative) and a fixed viewing distance. This DOF table calculates the extent
of the optical illusion of being in focus. The only points in actual focus
are those that bisect the plane of focus.

John Collier

Perhaps things are different in Texas where, I hear, they have a "plain" of
focus. :-)

> From: Rob McElroy <>
> If we assume, for this example, that the optical depth of field was say 6", if
> you look critically (using a loupe) at all three images, you will see
> that even with the wide-angle lens - anything falling outside that 6" DOF, IS
> technically out of focus (not critically sharp).  Here's the big BUT
> though.  With the wide-angle lens, our brain recognizes many OOF objects and
> doesn't think that those out of focus areas look too bad (not too fuzzy),
> but with the telephoto lens the OOF objects are almost unrecognizable (way too
> fuzzy) and our brain tells us that they are definitely OOF.  And no,
> this isn't fuzzy logic.

Replies: Reply from Rob McElroy <> (Re: [Leica] Re: DOF -Optical vs Apparent)