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Re: [Rollei] Re: DOF Indices, on R-TLR and other lenses
- Subject: Re: [Rollei] Re: DOF Indices, on R-TLR and other lenses
- From: Richard Knoppow <dickburk >
- Date: Tue, 13 Nov 2001 12:39:42 -0800
- References: <126.96.36.199.20011113025744.008f2140 >
At 08:39 AM 11/13/2001 -0500, you wrote:
>Richard Knoppow wrote:
>> FWIW, Kodak states that the depth of field charts published for their
>> large format lenses is based on a circle of confusion equal to 2 min of arc
>> or approximately 1/1750 of the focal length.
>> I don't know what criteria was used for the depth of field scales on
>> their focusing lens. I rather think it depended on the application and
>> assumed magnification of the final image. Kingslake may say something about
>> this in his old book on photgraphic lenses.
>Just to put the Kodak value in context, the DOF tables in my Rollei TLR
>manuals are calculated on f/1400 for 66 and f/2000 for Rolleikin, so the
>Kodak tolerances are stringent indeed...
Here is some more from _Lenses in Photography_ 1st ed., Rudolph
Kingslake, 1951, Garden City Books
He gives the following values for Kodak depth of field markings or charts
on various types of lenses:
8-mm cine 1/2000" (0.012mm)
16-mm cine 1/1000" (0.025mm)
24mm x36mm 1/500" (0.50mm)
Small folding cameras 1/200" (0.127mm)
Large cameras, critical 2min of arc (f/1700)
Large cameras, liberal f/1000
The discussion in the text indicates these are based on assumed typical
image magnification and viewing conditions. Kingslake has a very full
discussion of depth of field in this book with illustrations. He points out
that for cameras, like motion picture cameras, with interchangible lenses,
the depth of field must be calculated from a constant circle of confusion
rather than from one which is a fraction of the focal length.
There are some funny constants with depth of field. For instance, where
pictures are taken from the same viewpoint with two different focal length
lenses, and the images magnified to the same size, the DOF is constant with
the physical size of the diaphragm opening. That is, a half inch hole,
which is f/48 for a 12" lens and f/4 for a 2" lens, will have the same
depth of field when the image from the 2" lens is magnified to be the same
size as the other.
When the image size is adjusted to be identical by moving the viewpoint
the DOF will be constant with f/stop. i.e., if I place set up a camera with
a 12" lens and a camera with a 2" lens so that the actual images are the
same size the 12" lens will obviously be much further away from the
subject. At the same f/stop the depth of field of the two will be the same.
There was a second edition of Kingslake's book. I think I have it but
have a lot of books stored away. Both editions are reasonably easy to find
used and worth it. Very clear explanations of optics applying to cameras
intended for working photographers.
Los Angeles, CA, USA