Archived posting to the Leica Users Group, 1999/06/14

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Subject: Re: [Leica] Tri-Elmar and Depth of Field marks
From: "R. Saylor" <rlsaylor@ix.netcom.com>
Date: Mon, 14 Jun 1999 11:34:14 -0400

Slight correction.

The 30, 50, 100 rule was based on a .025mm circle of confusion, 
which I believe is consistent with Zeiss usage.

The Leica DOF scales appear to be based on a .03mm circle. To 
get the corresponding hyperfocal distances, use 26, 41, 83 instead 
of 30, 50, 100. (Not quite as neat.) 

The general formula is H = (F*F)/(f*c), where F is the focal length, f 
is the f-stop, and c is the diameter of the circle of confusion. This 
will give the hyperfocal distance H in millimeters. Move the decimal 
point three places to the left to get it in meters.

Richard S.