What to do with front focusing Jupiter-9

[Hamster]

I have a silver LTM Jupiter-9 that is front focusing by quite a bit. I have calibrated the lens mount to ling up correctly with my M4, however the optical block seems to be front focusing by a fair bit, even with all the shims removed.

As far as I can tell, I have the mount lined up correctly with the rangefinder cam and the main helicoid is racked back as far as it can go. The lens is very good condition and I suspect it was out of alignment right from the factory.

Am I doing something wrong? I have the same lens in M42 and would love to use it on the M4.

 

[clayne]

Does it hit infinity?

 

[Hamster]

Nope. It is focusing short of infinity.

Does it hit infinity?

 

[clayne]

Nope. It is focusing short of infinity.

Sounds like the helical is just simply off, starting thread wise. You'll need to use trial and error with ground glass on the back of the film rails with an actual camera to roughly assert it hits infinity after changing the helical starting thread. Then you can fine tune things. An SLR would make this massively easier but it's still possible to resolve this issue if it were just a simple reassembly error by whoever had it last.

This is assuming that the lens is grossly off already and basically allowing more close focusing than normal at the expense of infinity (like a permanent small extension tube). If it's close enough that shims would handle it then I'm not sure what the issue is.

 

[gb hill]

I read Brian Sweeny commenting that a J9 is impossible to adjust correctly. one reason I never got one. I have seen others that seemed to work fine. I have a J-3 that was front focusing & I fixed it by adjusting the rear element as close to the film plane as it would go & took out the 1mm shim & replaced with a paper thin shim. I don't know how similar the J-9 is to a J-3 as far as similarities of adjustment goes.

 

[johannielscom]

The Jupiter-9 is impossible to get in line with Leica over the full length of focus. But it can be adjusted to either focus correctly in the closest ranges, or at infinity. Whichever you prefer.

Only exception to this is quite unknown: if you have a real early one (starting with 50 or 51 serial number, or marked 'ZK') and the index marks for focus and aperture are approx. 7 mm off, you might have one that has a Zeiss optical block installed. In that case it's not a 85mm but an 83.7mm lens and it perfectly aligns with a Leica over the full length of focus...

 

[clayne]

Sounds like the inherent flange distance of these lenses are off for Leica, period. I agree with the others above that it's a pick your poison - either close or infinity. If I were you I'd target close-focus and accept that it'll never reach infinity (less used anyways).

 

[johannielscom]

^^Plus, at infinity DOF is bigger anyway, covering any focusing error at least partially.