Archived posting to the Leica Users Group, 2012/10/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]My understanding is that film has "depth" and a dgital sensor has almost no depth. So if the lens isn't focused on the active plane of the sensor, you are defocused. Second, I can understand that the optimal focal plane of the lens is dependent with f-stop, and was set to the focus mount to a larger tolerance during "film days". Now with digital days, it is much more important to set the focal distance to tighter tolerance, and also to determine which f-stop to use to set the focal distance. Vick On 10/12/2012 1:51 AM, Herbert Kanner wrote: > I'm gonna add some fuel to this fire. Maybe there is some technical > witchcraft going on that I don't understand, or maybe some of you guys are > just plain superstitious and Leica is talking a lot of impressive bullshit > about lasers and suchlike. > > So here is the understanding I've had for years as to how Leica worked > interchangeable lenses with a rangefinder mechanism. > 1. The rangefinder was designed to work with a 50mm lens in that the as > the lens unit moved to and from the film plane, the real end of the lens > container pressed against a roller on a lever that actuated the > rangefinder mechanism. Other lenses used a pair of threads (the technical > term being differential threads) so that as the lens focussed (with > greater motions if the focal length was more than 50mm and lesser motion > if less than 50mm) the rear cylinder would move the same distance as that > of a 50mm lens. With that kind of system, the only adjustment that would > be possible would be setting the infinity stop and setting the distance > marking ring to agree. > > Also, there is absolutely no reason for a digital camera to have any > different focussing problems than a film camera. It just that the focus > might be a bit more accurate since the sensor is rigid and there is always > the possibility, despite a pressure plate, that the film is not exactly in > a plane. > > Herbert Kanner > kanner at acm.org > 650-326-8204