Archived posting to the Leica Users Group, 1999/01/12

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Subject: Re: [Leica] Ground glass focusing check on M cameras
From: Ken Iisaka <>
Date: Wed, 13 Jan 1999 10:20:15 +0900

Harry Haige wrote:
> When used with a high power magnifier, this setup will reveal the
> full strengths and weaknesses of the focusing accuracy and lens
> quality.  For instance, you will be pleased to be able to read
> the fine print in a newspaper at 15 feet with a 50mm lens and
> surprised to see that (unless it is an APO) your lens clearly
> cannot focus red and blue targets at the same distance setting.
> No telling what your comparison of the rangefinder focusing
> indication with the actual image focus at the film plane reveals.
> There are many variables involved so don't be surprised!

Of course, our own eyes' chromatic abberations come into play, too.

Calibration is perhaps best performed using sodium vapour illumination,
or with a filter between the eye and the focal plane. :) :) :)