Re: [Leica] Re: DOF, thanks Austin

["Jason Hall" <JASON@jbhall.freeserve.co.uk>]

- ----- Original Message -----
From: "Austin Franklin" <austin@darkroom.com>
To: <leica-users@mejac.palo-alto.ca.us>
Sent: Thursday, February 08, 2001 5:31 PM
Subject: RE: [Leica] Re: DOF, thanks Austin


> > No, with respect, you're not addressing my point, Austin. DOF
> > as commonly
> > used (eg in published DOF tables, lens engravings and
> > published formulae)
> > refers to DOF of an image at a particular nominal
> > magnification and has for
> > fifty years. Your definition doesn't.
>
> I believe DOF (ie, engraved on a lense) is referenced to the film,
not to
> any magnification.

Wrong!!!  The depth of field scales on lenses are calculated based on
the COC that the manufacturer finds acceptable.  The "circle of
confusion" is typically calculated as the largest on-film circle that
you see as a point when you make an 8 × 12 print and view it from a
"normal" viewing distance.

The circle of confusion commonly used in the online tables, etc, is
based on the "Zeiss formula": d/1730, where d is the diagonal measure
of the film, in millimeters.

I do not understand why some people cannot accept that the generally
accepted definition of coc and depth of field is in fact tied to film
size.

Jason Hall