Archived posting to the Leica Users Group, 1996/07/22
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>Gerard:
>
>I am sure you know more German that I do. Actually, I believe the literal
>translation of the German word would be "measurement searcher" of which the
>English word "rangefinder" is the closest equivalent. Correctomundo, my good
>man!!
> The German word "Mess" translates as "measurement" or maybe "measuring".
"Sucher" means finder. Another english equivalent therefore may be
"measuring finder" but we agree that the term "rangefinder" is the best
equivalent in photographers language. How right we were!
At the risk of annoying our group with technical detail, and knowing that
the essential point of the question has been answered already, here is the
detail on the baselength issue, a bulk answer to a number of messages.
1. The baselength of the rangefinder is the same for all M-Leica's: 69,25mm.
2. The rangefinder magnification for the M3 is 0,9x, which gives an
effective measuring base of 63,3mm.
3. The rangefinder magnification for the M2/M4/M5 and M6 is 0,72x, which
gives an effective measuring base of 49,9mm.
3. A point is generally accepted as sharp at 0,03mm or smaller (depth of
field tables are based on 0,03mm).
4. Given above data, one can calculate the largest aperture, for a given
focal length, that the Leica M rangefinder can handle with 0,03mm precision
(the formula is in a German book on optics: ABC der Optik, Hanau 1972).
5. The results are the following:
Focal length M3 M2/4/5/6
--------------------------------
largest aperture
--------------------------------
21mm 0,12 0,15
28mm 0,21 0,26
35mm 0,33 0,41
50mm 0,67 0,84
75mm 1,50 1,88
90mm 2,17 2,71
135mm 4,88 6,10 (without glasses!)
--------------------------------
6. The glasses of the Elmarit-M 2,8/135mm magnify the baselength of the M2/4/5/6
with a factor 1,08, increasing the effective base to 74,8mm. This gives
higher precision than focussing the same lens on a R camera.
7. If you compare focussing on a M and a R camera, the main difference is
that M cameras focus with a fixed base (49,9mm), not dependant on the lens
used, and R cameras with a variable base, dependant on the lens used.
8. The measuring bases of R camera's, with different lenses, are the following:
Focal length effective base
-----------------------------
21 1,63
28 2,78
35 4,43
50 9,82
80 23,11
90 29,20
135 65,70
9. From the above its is clear that M-Leica's focus more accurately than
R-Leica's for lenses up to a focal length of approximately 125/130 mm.
Beyond that point the R-Leica's offer more precise focussing.
Back to picture taking now!
Gerard Captijn,
Geneva, Switzerland.
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