Archived posting to the Leica Users Group, 2013/01/06
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Hi Frank, Alpa supplies the shims with the mount for the back. They make mounts that work with HV, H, Mamiya, Pentax, and other cameras. Shims supplied with each. There is a YouTube that shows you how to calibrate your MF back to the Alpa body: http://www.youtube.com/watch?v=ajteLwe-ntE It's a two parter... Basically you take a non-wide angle lens (I use the 80mm), fully open it up and put the len's at it's infinity focus position. Then, on a clear day, you shoot something at least 2km away with some detail. Then you move the focus just a titch closer than the infinity mark (which moves the lens element further from the back) and compare that to the first image. If the stuff at infinity is crisper in the second shot than the first, you begin adding shims in .01mm increments. If it's not crisper you take out shims in .01mm increments. At some point in the process, the difference in clarity is undeniable and deteriorates with the addition or subtraction of just 1x.01mm shim. So you need your computer when you do this to read and display the files. It's a back of the car or an on top of a building thing. Once done, however, you're done. With Alpa you only need to do this once and it works for all lenses. With other tech cams (e.g. Cambo) the process is different; usually each lens has to be calibrated and the focus ring change... Bob On Sun, Jan 6, 2013 at 2:47 PM, Frank Filippone <red735i at verizon.net> wrote: > That is fascinating.....! > > I always suspected it was not as easy as taking out of the box and > shooting....... > > So how did you get the shims? And did you do the "calibration" yourself? > > Frank Filippone > Red735i at verizon.net > > I found the GG not to be reliable on these technical cameras with medium > format backs. I had been using the ground glass, which, though it looked > sharp, often was not. These sensor are so remarkably flat that even being > off 1/100mm will cause out of focus images. That's why Alpa allows users to > shim the piece that holds the digital back onto their cameras to be > adjusted > with shims by 1/100mm. Other digital technical cameras allow you to adjust > the focus point of each lens to the back. The manufacturing tolerance of > the > back's mounting plates are not within this range. > > The difference between my traded in back and this back was .1mm (the back > had to be positioned .1mm closer). > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information > -- Bob Adler