Archived posting to the Leica Users Group, 1997/09/17
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]> 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