Archived posting to the Leica Users Group, 1999/04/11
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Just a few thoughts about the film scratches this Sunday morning. In the early days of the M-3's, the pressure plate was ceramic, if my memory serves me correctly, but that was changed when static electricity discharges on the film were apparently traced back to the film rubbing across the ceramic plate thus generating static electricity. At least that was the story in the 1950's. Polishing the current pressure plate. It is likely the current pressure plate is an aluminum alloy that has been plated or anodized. Thus, if it is polished with fine abrasives such as silicon carbide paper or crocus cloth, the surface may be removed. If the pressure plate is aluminum and the anodized surface is removed, the very soft aluminum will likely pick up specs of dirt and grit that will really cause a scratching problem. If the surface is anodized, the surface will be harder than tungsten carbide and should not be removed in my view. Another problem is getting the pressure plate too smooth. If the plate is too smooth, the film may "wring" to the pressure plate just like Jo-blocks ring together. Then you would really expect to see scratches on the film since the film would stick to the pressure plate and resist moving across the pressure plate. There is a fine line between getting a surface too smooth and not smooth enough and each application requires its own specification. Further, if the black finish is removed, light will travel through the film, reflect off the pressure plate and begin a return journey through the film from back to front this time thus degrading the film image. I am looking at the pressure plate on my M-6 that was purchased about 6 months ago and the finishing marks are NOT in a straight line but somewhat circular which leads me to believe the pressure plate was finished on a flat lapping machine that employees a lapping wheel to provide the final finish. I have just checked my old M-3 pressure plate and the finishing marks appear identical to the M-6 so the manufacturing methods must not have changed much over the years. One of the LUG members suggested taping protective covering over the rest of the camera while sanding the pressure plate to keep out the grit generated from that operation. If an M camera owner is going to attack the pressure plate, I would suggest he or she remove from the camera body the back cover on which the pressure plate is mounted. The left hinge moves laterally by pressing the stop pin to the right which should allow the back cover and pressure plate to be totally removed from the camera body. It is likely ALL of the abrasive used in the effort to further smooth the pressure cannot be cleaned out of the back cover and it will eventually get into the works of the camera and really make a mess of things. If there is a spec of grit on the pressure plate, you will probably be able to see it by using a strong light and positioning the pressure plate in relation to the light to get a terrific view. You will likely be able to see specs so small that they would not put visible scratches on the film backing. Why not return the camera to Leica with the scratched film so the matter may be properly examined and resolved. May be that the factory let out pressure plates that are either too smooth or not smooth enough. Bringing it to the attention of the company would benefit everyone involved. It might even be worth a call to see if Leica would send you a back cover while yours is in the shop since the back cover is removable. Good luck with the project! DonjR43198@aol.com