[Leica] Rangefinder error on M9

[hopsternew at gmail.com (Geoff Hopkinson)]

Hi Howard. Don't be afrraid! Always a learning curve with new hardware ;-)
Some suggestions from me on possible factors here.
Firstly a sensor has effectively 'zero' depth vs. film with some curve and
thickness. So errors that may have always been present are more apparent.
That is exacerbated by the capacity to pixel peep afterwards, of course, not
to mention the availability of immediate processing.
You comments that you are OK at infinity but not at 7m suggest that any
issue may be worse at close range (dependant on whether you have a front or
back focus condition of course). Even wide open your lens should have about
~750mm acceptable depth of field at 7m. It would need to be a fair bit out
for your target to be soft then. Possible that the extra DoF at infinity is
masking an error which may in fact be worse there though.  But do some
careful testing including the most critical conditions of wide open and in
close. Try a magnifier too if you can. Can you test your lens on another
digital M and others lenses on your camera? Obviously any apparent
error may be in the camera and/or lens or neither.
I don't know what if any focus shift (on stopping down) is present with your
lens model. I don't recall reading any reference to a problem there. Still
it is something else to consider

In answer to your last sentence. No that is not true, although it may be
possible to arrive at a compromise that works well enough with your
combinations.  However what you want is a camera at the exact factory
specifications and the lenses the same, not equipment adjusted to work best
with just one or two specific lens samples. Your camera should be spot on as
delivered of course and the factory calibration process is extremely
precise.  Leica Camera test them at each metre out to 7m on  their massive
test rig in fact. That evolved from lessons learnt from the earliest M8
production. It is not impossible that it delivered out of adjustment or
moved since new but its more likely that your camera is not at fault. At
least that's the best assumption to start with.

You're (still?) in the SF Bay Area I think? A number of M9 LUG folks there
you may be able to collaborate with for testing.

Cheers
Geoff
http://www.pbase.com/hoppyman


On 7 November 2010 08:26, Howard Ritter <hlritter at bex.net> wrote:

> I have just discovered that the RF on my M9 does not bring the 90 ASPH to
> focus in at least the middle range, specifically 7 meters, although it does
> so, as far as I've been able to tell, at infinity. I have not tested it
> thoroughly at closer range, but I'll do so tomorrow during daylight when I
> can use a low ISO.
>
> I had seen comments on LUG/MUG along these lines previously but not paid
> attention because I didn't yet have an M9. I recall seeing something about
> lenses needing modding in order to focus properly on the M8 or M9, but 
> can't
> recall details.
>
> This is very counterintuitive and perplexing to me. Given that the
> flange-to-sensor distance on digital Ms is the same as the flange-to-film
> distance on analog Ms, how does the problem arise at all, and why does a
> modification of the lens or adjustment of the RF mechanism to accomodate 
> one
> combination not affect the modified unit's performance with other
> combinations?
>
> Any insight or advice would be highly appreciated.
>
> ?howard
>
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