Re: Body focus was [Leica] RE: Cosina still at it

["Dante A. Stella" <dante@umich.edu>]

Martin Howard wrote:

> > Think of the 200 parts in an M rangefinder.  Add up all of the individual
> > tolerances.
> >
> Yeah, but some are positive and some are negative and so they balance each
> other out to some degree.  Besides, there must be a tolerance for the focal
> plane too: it can move back and forth by some (small) measure and we will
> not be able to see the differance in the negative/print.  As long as the
> individual tolerances balance out to within this range, then everything's
> fine.  Which, I'm assuming, is standard mechanical engineering practice.

Certainly, but this is not the "right-or-replace" policy that Leica had.  It's
a modern engineering practice that started in the United States with Deming,
was rejected here and in Europe, traveled to Japan, entered their automotive
manufacturing, filtered through their optical industry, back into America,
Europe and finally into Leica.  And yes, you're right - the tolerances may add
up properly in a one-dimensional system.  But the mount plane and the film
plane can move in three dimensions (with 0.02mm tolerance, from what I
understand, for proper focus).  The only reliable way to cancel this out is by
adjusting one end, i.e. the mount or the film plane itself.

> > If you think otherwise, mount a very heavy lens on a rangefinder.  Line up
> > infinity. Flip it upside-down.  Notice anything?
>
> So what, don't use a Leica M in microgravity?  How many people do you know
> who use their rangefinder cameras upside-down?

That's not the point - it shows you that the weight of the lens bears on the
whole system.


> > -- Finally, any combination of the above.  This is the "system tolerance."
>
> But isn't the job of factory QC and aftermarket CLA to ensure that the
> "system tolerance" is within spec?

Factory QC definitely brings things to spec.  But what of the reassembly?  I
would be very surprised if any aftermarket CLA involved collimating at the
corners and the center of the film plane.

>
> I think the solution is simple.  Grab a camera and one lens.  Grab 20 rolls
> of film.  Walk the streets for 10 hours.  Take pictures.
>

And take the whole thing on faith.  That's what it requires - I guess the point
of this is that we obssess about optics and not enough about keeping the rest
of the system in line.  Just get stuff that works together and run with it!