Archived posting to the Leica Users Group, 1999/09/11

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Subject: Re: [Leica] depth of field..depth of focus?
From: Martin Howard <mvh@media.mit.edu>
Date: Sat, 11 Sep 1999 14:04:21 -0400 (EDT)

On Sat, 11 Sep 1999, Ted Grant wrote:
>
> What think you folks?  The student is waiting, because I told him I'd
> present his question to the worlds "great photo minds for an answer!" :)
> 

Not that I fall within that category, but that has never stopped me from
proffering an answer ;)

As I understand it, `focus' has to do with the film plane.  When we talk
about focussing on a subject, it is not the fact that the lens is set to a
particular distance that is meant, but that the light rays from certain
plane infront of the lens converge at the plane of the film.

Consequently, `depth of focus' should refer to the film plane, not the
object space, or else we would be mixing two different definitions of
`focus', one to do with the film plane, one to do with the object space.
`Depth of field' is used to refer to the object space, to avoid this
confusion of the term `focus'.

OK, not the most technically clear presentation, but isn't that the
fundamental distinction?  Focus has to do with the film plane?

M.

- -- 
Martin Howard                                 (__)                 (__)
Visiting Scholar at MIT Media Lab |           (oo)                 (OO)
fax: +1-617-253-8874              |    /-------\/       ~~~~~~~~~~~~~~~~~~~~
email: mvh@media.mit.edu          |   /|     ||
www: http://mvhoward.i.am/        | ~~~~~~~~~~~~~~
                                  |   Cow in water         Cow in trouble