Archived posting to the Leica Users Group, 1998/04/19

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Subject: Re: [Leica] DOF indicator
From: Nick Hunter <nhunter1@mindspring.com>
Date: Sun, 19 Apr 1998 21:51:17 +0100

Thibault Collin wrote:

>Of course, but if we have free time this summer, we could try to calibrate
>it with other lenses which will give other apertures!! It would be a tough
>job!

Thib:

What an interesting idea! I don't know if I'll get around to doing anything
about it, but I think the theoretical answer would be as follows: Two stops
slower for twice the focal length. Therefore (approx.):

50mm=   f:5.6/f:16

75mm=   f:8/f:22

90mm=   f:11/f:32

135mm=  f:16/f:45

I stand ready to be corrected by LUG optical wizards. Remember I did say
approximate, and DOF is a tricky issue which can (and has) filled whole
books.

Nick Hunter