Originally posted by RioRico Ryan: The usual reason for M39 or M42 lenses (like the Jupe you mention) not hitting infinity is from using a flanged K-M42 adapter, which pushes the glass out just enough to be shortsighted. Some long teles, like my Spiratone 400/6.3, actually far-focus past infinity, so the flanged adapter corrects that. Flangeless adapters (sometimes labeled INFINITY FOCUS) like those from Pentax and Bower, don't have that problem. Of course, if you're using the Jupiter-9 for portraits, you don't really need infinity, right?
I meant to say...some M39 lenses have a registration distance (from rear lens element to film plane/sensor) shorter than their M42 counterpart. There were M39 lenses which had the same distance as M42 for SLR cameras (Zenit), and I also believe some were made in Leica Thread Mount M39 for Fed or Zorki rangefinder use.
So...basically identical lenses incompatible with different M39 cameras depending on registration distance...or at least that's how I understand it...
Originally posted by Ira And Yumpsh (and others), I found quite a few sources on eBay for 39mm to 42mm adaptors, but some of the sellers are specifically mentioning 39mm Leica, where others just say 39mm.
Aside from the material and quality, these are all the same, right?
The adapter is just a piece of metal...as long as the diameter and thread pitch is the same, you're ok.
LTM is 39mm diameter and 26 threads per inch, which is cross-listed on camerpedia as just M39
This is a discussion about Leica rangefinders, so insert [Pentax] and [M39] where required. Hopefully this helps and doesn't confuse...
Edit: Here's what I get out of all this.
Leica Thread Mount or L39 is for rangefinders and will not focus to infinity. If you can focus to infinity by putting the lens up to the camera mount, you need a standard "non-Leica" adapter for M39x1 thread pitch.