Topic: Jupiter 37A infinity mod
Hi there, here is my 2cents...
I am using Pentax DSLR and I play with m42 lenses, Russian made mostly as they are low cost but not 'cheap', I always have problem with the adapter, those 'flush fitting' adapter that allows infinity focusing is hard to install and remove, quite trouble when I need to change lenses in middle of shoot, so I decided to stick with the non flush type, but I only able to do close focusing then, there is exception with mirror lenses, as they focus pass infinity (compensate for temperature change), more than enough to offset the adapter thickness.
Just recently I pick up a Jupiter 37A, which is a very sharp 135mm lens, with non flush fitting adapter I can only focus to about 20m, after looking at the inside of the lens I found a simple way to push the 'infinity lock' further, and this is completely reversible, but by doing so the focus scale will become out of line, I think that wouldn't be a problem, as we will focus by eye or use AF assist anyway !
Here is how to do it 'at your own risk !'
Simply remove the m42 mounting at the back of lens which locked by 3 screws, after that you will see two L-bracket at the sides of the lens assembly, they are used to limit the optical block from completely unscrew from the lens body. Remove only the 4 screws that holding the L-brackets, then turn the focus to the far end, so that the L-brackets shifted by one hole, that little adjustment moves the optical block further to the focal plane, thus bring the lens into near infinity focus. Put back only one screw at both L-brackets, or you can drill holes for the other screws but not necessary, put back the m42 mounting that's all !
I am still looking for ways to adjust my Mir 1B, Pentacon 30mm/3.5 and Pentacon 135mm/2.8 any idea ??