Thanks all... keep em coming. The Jupiters concern me because you have to do some mods to make them work on M cameras (is this true?)...
You have to do some mods to make Soviet lenses work on ANY camera, even their "parent" Soviet ones!
😛
Soviet quality control is, well, there wasn't any, so a large number of lenses misfocus because of poor calibration - applies to all Soviet lenses, whether Jupiters or Industars. When I got my Jupiter 8 , not only did it misfocus but one half of the photos from it was sharper than the other!
On the plus side, the misfocusing is easy to fix: take apart the lens and grind down or add padding to the shim (plenty of info on the web, e.g.
http://www.pentax-manuals.com/repairs.htm).
The Jupiter 8 and Industar 61 are surprisingly good lenses (when the focus correctly!). The Jupiter 3 and other industars (see wlewisiii's post) give a more "old fashioned" look - I'd plump for an older Industar because Jupiter 3s are quite pricey. As the Industars are so cheap, you can sandpaper the lens if you want more character".
If such a thing as a used-camera shop still exists in your neighbourhood, ask if they have any unwanted Soviet lenses - mine gave me some for free (a bit tatty, all misfocused [not that the shop had ever checked], but all working). Can't get cheaper than that!