[Leica] Rfdr. Accuracy Test Results

[nbwatson@juno.com (N. B. Watson)]

Well friends, being the I've-got-to-prove-it-to-myself type, and what
with all this talk about the new 135 lens and HM vs. "classic"
viewfinders, I had to do a definitive experiment to put my mind to rest
and I hope it's useful to you folks as well...I encourage anyone who
cares, to try this for themselves:

I made a temporary ground-glass focussing screen by taking the backflap
off my M4-2 which just returned from a Leica CLA, and taped a focussing
screen (frame-less type with microprism and split-image from a Nikon
FE-2) flat against upper and lower film rails, *matte side facing the
shutter*. [BTW and FYI, I confirmed the accuracy of using the Nikon
screen for this, with an actual piece of view-camera ground-glass. The
SLR screen is brighter and easier to see cricitally]

I then replaced the baseplate and mounted the camera with 4/135 lens
attached,  on a tripod.  Using a locking cable release, I locked the
shutter open on "B" and aimed the camera at a wall on which I had taped a
newspaper page with a black, vertical 1mm-wide line I had drawn with a
felt pen and a rule.

With the lens wide open, focussing alternately with the rangefinder and
on the ground-glass (using an 8x APO focussing loupe and examining the
matte, microprism and split-image) at distances varying from the lens'
minimum (1.5m) to 10m, I found that the rangefinder was not just close,
but *dead-on* in agreement.  I repeated this test outdoors using
contrasty vertical-lined objects from 10m to infinity, and also with my
M6 0.72x. (Of course, since DOF decreases with subject distance, my
close-range test was the more critical).

Bottom-line, friends, is that whilst * I do not dispute* the immutable
optical fact that the higher magnification finder is more accurate, I
have convinced myself that the 0.72x rfdr is more than up to the task of
critically focussing a 135 lens at f4, and the DOF of the 3.4 would not
be dramatically less, up to the lens' near-focussing limit.  So anyone
who is contemplating buying an HM with the *primary* reason of focussing
accuracy with 90 and 135 lenses, and has mixed-emotions about losing the
28mm frameline (or the 28 *and* the 35 if you wear glasses), I strongly
urge you to take an hour and perform this test for yourself.  Or simply
run a test-roll of Velvia using similar target subjects.  I have already
done this, too, and I will run it through the Jobo ATL tomorrow morning
and see what develops.

A good weekend to all!

Regards,
Nigel

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