Hi! As you know I have a Helios 44K4 (formerly 58mm f2) lens modified to be a single element soft lens. The process of making this kind of lens has many side effects ;-)... One of those effects is that focusing range is thrown out of whack. It is usually taken care of by attaching an extension ring between the lens and the body.
Originally, when my monocle was made, I used Pentax #1 extension ring. It did not solve the problem completely. That is, I could focus far beyond infinity ;-), and the closest focus distance was rather far. Today I received Kenko 12 mm ring and tried it... I think I achieved the perfect infinity focus and then of course proper close focus distance too. According to Boz's site, Pentax #1 ring is 9.5 mm in height. So here is the question... Is there a way to actually compute the distance between the glass element and focal plain? Or in other words, is there a way to compute the height of the extension ring to be inserted? Do I have to know the curvature of the glass element in order to make this computation? Thanks in advance. -- Boris
