Re: Film flatness etc. (was Ed at Modern)

[Edward Meyers <aghalide@panix.com>]

On Wed, 17 Sep 1997, Kari Eloranta wrote:

> > From: Edward Meyers <aghalide@panix.com>
> 
> > My thoughts go to making photographs with lenses and that the lens
> > doesn't stand alone. It's has a camera to go along with it. So,
> > I lens should be tested with film on the camera, not on an optical
> > benchwhich gives you theoretical answers that are electonically
> > converted into make-believe prints.
> > One concern is the film channel of a camera. Bob Schwalberg noted
> > much about this to me during our many lunches in the big apple.
> > For example: The screw-mount Leica's film channel is not so good.
> > The M camera is much better. The old Nikon F was excellent.
> 
> Solid point!
> 
> In the process of sorting out the focusing problem in my M4-P I ended up
> doing the following experiment as well:
> 
> Reload a strip of uniformly exposed film into the canister. Load it into
> the camera as ususal, advance a few frames and leave the shutter open at
> B. Remove the lens and look at the black film surface. In particular look
> at the reflection of a circular light from the film. It can be anything
> from oval to irregular and certainly varies from edge to center. And
> depending on whether you have film with stiff base or a thinner one you'll
> see different things. If you poke the film (with some blunt object) you'll
> get a feel of how much play there is between the film and the pressure
> plate at various parts of the frame.
> 
> This should convince anyone that testing a lens separately is not
> sufficient if one wants to assess what the final image is like. And in
> particular things like the image flatness of Summicron 35 ASPH versus the
> non aspheric seem a bit of academic after this.
> 
> BTW my M4-P came back from the third service trip from the factory in
> less than two weeks with apologies for the missing framelines. But it
> 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.
> 
> He also said that whenever any of their customers gets a Noctilux its
> bayonet is matched to that of the body for the reasons above.
> 
> 
> Kari Eloranta
> 
> 
> 
> 
> 
> 
> 
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