Archived posting to the Leica Users Group, 2000/11/11

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Subject: [Leica] DOF + M6 modifications
From: Robert Appleby <robert.appleby@tin.it>
Date: Sun, 12 Nov 2000 08:37:52 +0100

>>>>>
What you call film-plane DOF is not soley determined by subject distance,
focal length, and aperture.  It is also determined (and this is *critical*)
by the size of the CoCs that you are willing to accept.  I believe that in
35mm photography, a standard circle-of-confusion size is 0.03mm.  If you
plug a different CoC size into the equations, the DOF will change even
leaving the subject distance, focal length, and aperture the same.

Once you stop thinking of DOF as an objective property and start thinking of
it as "the zone of perceived sharpness around the focus plane", you realize
that DOF "around" the subject, on the negative, and in the print are all
just different ways of looking at the same thing.  It is just a convenient,
standardized representation of the limits of visual perception as it
pertains to photography, and not conceptually different entities.  Outside
the equations, in the "real" world, DOF doesn't exist.
<<<<<

Well, I got all of that Martin. After all, even the definition of focus is
going to change from lens to lens. I wasn't thinking of it as an inherent
property of the lens but as determined by those factors when the CoC thing
had been set. But I didn't say it! Incidentally, I believe Zeiss uses a
factor of 0.02mm for their depth of field markings, is that right? I read
it somewhere, maybe on Erwin's site. But since I don't have any Zeiss
lenses I can't compare their markings to the Leica ones.
Still this discussion did clear something up for me, which is now making MF
look much more attractive!

"Outside the equations, in the real world..." - Martin, you know better
than that!

As to the 4mm spacer, I don't think there'd be much profit margin in
something like that. It wasn't cheap for me! Tom A would be the best person
to do it, I suppose, since he's already tooled up.
As I said I find it a very real improvement on the existing shutter dial.
And it doesn't interfere with the Voigtlander or Leica accessory finders.
You lose the flat-topped Leica look, though. 
The battery cover - well, I already had the knurled cover on my cameras but
they seemed to lock up so this was a solution. One of the original covers
is now missing its leatherette because that came away while I was trying to
unscrew the damn thing.

Rob.
Robert Appleby
V. Bellentani 36
41100 MO
Italy
tel. (+39) 059 303436
mob. (+39) 0348 336 7990

Replies: Reply from Jim Brick <jim_brick@agilent.com> ([Leica] Re: slotted battery cover)
Reply from Mark Rabiner <mark@rabiner.cncoffice.com> (Re: [Leica] DOF + M6 modifications)