Jupiter 9 Back Focuses on ZI

[drjoke]

Now what?

I bought Jupiter 9 off Ebay because I wanted a cheap alternative to ZM Sonnar 85mm. I forgot to read about this lens compatibility, and it seems other people have issues.

What do I do now? Is this something I can fix myself? Or do I need to find an expert to send this lens off to?

 

[Mazurka]

It's always a good idea to read threads started by yourself: http://www.rangefinderforum.com/forums/showthread.php?t=46487

Get a Zorki or Fed camera (do a search) if you still want to use the J-9. Sell or write it off if you don't want to gamble any further.

 

[Kim Coxon]

It is a common problem with the LTM J9s and relatively easy to fix. You need to thin the shins between the two lens groups to effectively shorten the focal length and then thin the main shims to ensure it focusses at infinity. It can be a bit of trial and error. With the black ones, you may need to "thin" the aperture control ring depending on how far out it is at the moment. You may find that it is also out out an FSU body as well.

Kim

 

[ZorkiKat]

Get a Zorki or Fed camera (do a search) if you still want to use the J-9. Sell or write it off if you don't want to gamble any further.

A good J-9 will be good regardless of where it's put on. My J-9s work well on both my LTM and M Leicas. J-9 belonging to my friends also work on their respective non-FED or Zorki (Canon, Bessa, and other Leica) cameras too. In fact, I've found at times that the J-9 on a Leica does better than a J-9 on an improperly adjusted FED or Zorki.

As Kim has said, some J-9 may need adjustment. The reason why they don't focus right is likely due to some improper servicing they received.

It's not always a shimming issue though. In many cases, it's the improper assembly of the three helicals which the J-9 uses. They're easy to take apart, but diffcult to put back properly. The multiple entry threads would allow almost an infinite ways to putting them together, but only one will be correct.

Jay

 

[Kim Coxon]

The correct way to get the helix's back together is covered here: http://www.pentax-manuals.com/repairs.htm
As far as the helix is concerned, this affects primarily the RF coupling. If the lens focuses st infinity but back focusses at close range, then it will be a shimming problem and not the helix. 😉

Kim

It's not always a shimming issue though. In many cases, it's the improper assembly of the three helicals which the J-9 uses. They're easy to take apart, but diffcult to put back properly. The multiple entry threads would allow almost an infinite ways to putting them together, but only one will be correct.

Jay

 

[ZorkiKat]

The correct way to get the helix's back together is covered here: http://www.pentax-manuals.com/repairs.htm
As far as the helix is concerned, this affects primarily the RF coupling. If the lens focuses st infinity but back focusses at close range, then it will be a shimming problem and not the helix. 😉

Kim

Some of the 'back focusing' issues may actually be RF coupling issues. An improperly assembled helical may show correct infinity camming(ie, the cam extension length is right) but loses this as the helicals move to focus for more intermediate to close distances.

I've had several J-9s which have been shimmed properly - when focused through a groundglass on an LTM camera, infinity focuses on the dot- and appear to have correct RF camming at infinity as well. But these same lenses lose RF camming/coupling accuracy as they focus closer. For instance, with one of these J-9, the camera RF would make the lens to focus at 4 mtr for a target 3 metres away.

Focusing these lenses using their distance scales would show correct focus on the groundglass too, but the camera RF patch would show something else. Their helical RF camming is not quite right - the back extension length to couple with the camera's RF sensor isn't of the right value.

Taking the helicals apart and putting them back over and over until the correct (ncessary) cam lengths at various focus settngs were obtained made these lenses focus correctly.

One J-9 (not mine) which I got to look at had a strange affliction. It appeared to be correctly calibrated from infinity to about 1.2 mtr. But at 1.15 mtr (the lens' closest focus), it wouldn't couple correctly. The camera it had been on was a Bessa.

Jay

 

[Iggy]

Just bought one of these from a guy in Poland (via ebay). Maybe it'll be a good one, maybe it won't but it cost less than £50 including postage so I see it as a worthwhile gamble.

 

[drjoke]

I am no mechanic nor carpenter. Is there someone who is good at these kind of things that I can send my lens to, for a fee?