Re: Film flatness etc.

[Kari Eloranta <kve@dopey.hut.fi>]

> From: Edward Meyers <aghalide@panix.com>
> > KE wrote:
snip
> > still needed the bayonet changed. While all this was worked out I talked
> > quite a while with an experienced service technician. Among other things
> > he said that most M's are originally a bit "fat" - they are made perhaps
> > one or two hundreds of a millimeter too thick (distance from bayonet to
> > pressure plate) to accomodate the wear from lenschange. If the thickness
> > is at the tolerance limit the camera may have a focusing problem IF the
> > lens' tolerance it the same way i.e. the whole assembly puts the lens
> > too far from the film plane.
> >
> Maybe Leica figures that the new owners of M6 cameras tend to
> hold them tight and therefore end up squeezing a little. I'm
> sure that there is a tolerance, but I cannot believe that they
> would make the camera fatter and beyond the tolerance. Ed

No, they don't make it beyond tolerance. But there is some tolerance
allowed for body thickness, bayonet thickness & barrel length. As with
any industrial product there will be some variability. If you don't allow
any there won't be anything coming out of the production line. Chances
are you'll newer see the "error" unless you shoot test target fully open.

What I said is that if the tolerances for both the lens and the body add
up and don't cancel (both items can be too short/thin or too long/fat)
i.e. the errors have same sign, there may be a visible result of fuzziness
in the image.

This sort of thing doesn't get caught in a plain lens test (without a
body that is). My Summicron 50 has fine glass, the centering seems dead
on etc. But with it's new bayonet it "conspired" with the slightly too
fat body.

Interestingly when a body and lens combination is sent to the factory the
items are handled by different people in the service dept. They don't
test them together(even when the reason for the items coming in is a
focusing problem).

The sevice guy (factory trained) that told me about these things also had
a few body bayonet rings that were milled to certain thickenesses for
exactly this matching operation.

No, I don't waste film on test targets any more than I have to. I find it
is much more rewarding to shoot fuzzy targets like fellow human beings 
:-). But when the factory really screwed up I wanted to find out what was
going on and if they did anything at all right while the equipment as
there. I'm relieved the hassle seems now to be over.


Kari