[Leica] DOF scales on Leica, Hassy lenses

["Oliver Bryk" <oliverbryk@home.com>]

After following the DOF thread - or, more accurately, attempting to follow
its occasional branchings - for some time, I remembered that I had inquired
about the circles of confusion (CoC) used in marking Leica's and
Hasselblad's lenses, respectively. FWIW here are the answers, retyped from
the printouts (I no longer have the messages, and I have changed my e-mail
address).

(From Leica):
"Subject: Re: Circle of Cunfusion
Date: 19 Jan 2000
From: Olesin@aol.com
TO: obryk@flash.netdex.com

The size of the CoC upon which we mark depth of field scales is 1/30th mm.
I'm afraid the actual mathematical formulae are left to textbooks on optics,
as we are unfortunately not equipped to delve into the theoretical
background. This should answer at least half of your question. Thank you for
your e-mail."

(From Hasselblad):
"Subject: Ang: Depth of field scales
Date: 19 Jan 2000
From: erland.petterson@hasselblad.se
TO: obryk@flash.netdex.com
CC: torbjorn.eriksson@hasselblad.se

Dear Mr. Bryk,
The circle of confudion (sic) has a diameter of 60 microns. The indications
on the lens barrels are theoretical distances for different apertures for a
lens without other lens errors. This means that diffraction effects is (sic)
also not included.
Our recommendation is to take the indicated depth-of-field with some care.
If you need good quality we recommend to only use half the indicated DOF.
For example if you use aperture f/11 you should consider DOF for aperture
f/5.6 as good quality.
Sincerely yours,
VICTOR HASSELBLAD AB
Erland Petterson
Product Manager Camera Systems
(phone, fax nos)"