[Leica] Received M8 & lenses repaired/adjusted by Solms

[pklein at threshinc.com (Peter Klein)]

Peter:  I know what you're going through. Leica should make good on your
problems, but the issues are complex, and some real-world compromises may
be needed.  Let me give you an overview of the situation.

Those of us experienced with film Ms tend to think of the Leica
rangefinder as a perfect device. And with film, for all practical
purposes, it was when properly adjusted. Nobody complained about focus
shift and back/front focus except with the Noctilux.

The digital Ms have much greater precision requirements for focusing, due
to the fact that the image-making plane on a sensor is a flat plane,
whereas film has thickness.  And the M8's lack of an anti-aliasing filter
means that you really see minute differences in focus accuracy.  When the
M8 came out, Leica was still adjusting lenses to film-M specs, which
wasn't good enough. Supposedly they've upgraded their equipment and
testing procedures.  But there are enough stories like yours that I
wonder.

DAG (Don Goldberg) in Wisconsin is the only person on the planet that I
know of outside Leica itself who can truly optimize lenses for the M8. He
will adjust your lenses using a known-good M8.  If necessary, you can send
him both your M8 and your lenses, and he will make sure both are up to
standard.  With Don, it may take a while, but you know he will get things
as right as they can be.  With Leica, it seems to be a crapshoot.

90mm lenses and very fast lenses are the hardest to get right. With some
fast lenses, you have a choice.  You can have a lens adjusted to focus
perfectly wide-open, in which case it will back focus at middle apertures;
or you can have it adjusted so they are perfect from f/2.8 and narrower,
in which case they will front focus wide-open.  I had DAG adjust my 35/2
pre-asph Summicron IV in the latter manner, since I mostly use it
outdoors.

My 35/1.4 Summilux ASPH came from the factory optimized for wide-open use.
 It back focuses slightly at middle apertures, but I know what to do to
get it right--focus on a person's nose instead of their eyes, or focus on
the closest thing I want in the zone of focus rather than the middle of
the zone. Since it's behaving exactly how Leica described it in a Leica
Fotographie article, I decided to leave it alone. I hand-code it rather
than send it to Leica, and risk an experience like yours. If it ever gets
out of adjustment, I'll send it to DAG.

Even DAG was not able to get my pre-Asph 90 Summicron to focus perfectly. 
But he got it close enough and consistent enough that I know what to do to
compensate when I use it in the theatre or concert hall. My old 1960s 90
Elmarit is hopeless on the M8, and it was fine on film.  My other 90 is a
Voigtlander 90/3.5 Lanthar, and it is perfect at all stops--so this is the
90 I use the most. Even Leica has admitted that faster 90mm lenses may be
beyond the accuracy of the rangefinder system on the M8.

Now the dirty little secret: All fast lenses have focus shift. It's always
been there, but we never noticed it on film.  With the M8, the question is
how much and whether it really matters. I can detect it on my tabbed 50
Summicron, but it doesn't really matter in practice. My 50 Dual-Range
Summicron (altered to mount on the M8) has so little that it can be
ignored. A lens like the VC 35/1.4 Nokton has a great deal of focus shift,
and it's never going to be perfect at all stops and distances.

This is one reason why Leica is creating new lenses with floating elements
(like the new 35 and 50 Summilux ASPH lenses).  Voigtlander solved the
focus shift problem on the big 35/1.2 Nokton by not correcting some
aberrations, such that as you stop down, the focus shift actually
oscillates back and forth slightly across the point the rangefinder is
actually focused on. I've reproduced this myself, and couldn't believe my
eyes. Erwin Puts told me that no, I wasn't imagining it, it was part of
the lens design. The result is a lens that is for practical purposes, free
of noticeable focus shift. The price you pay is in contrast.

So, getting lenses to focus correctly on the M8 is a complex process with
several variables:

1. Is your M8 exactly up to standard?
2. Is your lens exactly up to standard? (if either of these two factors
are off, you will have front or back focus at all stops. If the camera or
the lens cam is way off, you may have correct focus at some distances and
not at others).
3. How much focus shift does your lens have?  If focus shift is a
practical problem, then...
4. Do you want your lens optimized for wide open, middle stops, or some
compromise where it's almost right everywhere, but not quite? If the
compromise is sufficient for the kind of photography you do, great. If
not, pick the optimization you want. Compensate when needed, or use
different lenses for available light vs. outdoors.

I hope this is helpful.

--Peter