Jupiter 9 back focus

[crispy12]

I recently got a cosmetically great condition J9 85/2 however it seems to have problems focusing at close distances (1-2m from my first test) on my Bessa R2. The lens is back focusing about 10cm behind where I've focused.

I've searched around and it seems like a common problem for J9s, does anyone know how to fix? Here are some things I noticed:

1) It can be very hard to focus due to the short base length of the R2. The images don't move very much with a moderate turn of the focus ring. I start at minimum focus and turn the ring till the images start to align, then stop. Should I be starting from the other direction?

2) I checked a website on RF collimation, can anyone tell me if this is accurate for checking inf focus: I taped a thin receipt to the back of the camera (film plane) and set the lens to inf. It looks very sharp when placed against a bright light. I'll check with some film later. However close focus is more important for me as I want to use this as a portrait lens.

I get around by shooting this at f4, which works reasonably enough but not very satisfactory solution overall.

 

[mdarnton]

It's not a "problem"; it's what it's supposed to do. Russian "Leicas" have a slightly different focus curve than the real thing. Apparently it's possible to disassemble the lens and replace a few shims with different ones--one to change the focal length of the lens, and one to change it to its new infinity position with the new focal length, and that lens is one of the easier ones.

Someone will probably pop up to refer you to instructions. You may not be up to them if you're not mechanically inclined. One thing that's handy is to have access to an M series Leica so you can use a ground glass at the film plane. There may be someone online who does it commercially. . .

Or you can be one of the deluded ones who say it's "bad Russian tolerances", or insist there's not problem at all, and your photos are in focus. . . or other such garbage. Those are two common responses. 🙂

Once you get it set straight, it's a good lens.

 

[Chriscrawfordphoto]

To add to what mdarnton said (all of which is correct), you can only calibrate the lens for accuracy at one distance. If you re-shim it to be accurate up close, focus at long distances will be off in your photos (even if it looks in focus on your rangefinder) and if you calibrate it for accuracy at long distances, you'll get backfocus up close.

I had a J-8 and it made great images up close (mine was calibrated for close focus accuracy) but worthless at other distances, and that got real old real quick. I prefer gear that 'just works', no compromises. If you can afford it, I'd look into a lens made for Leicas. The Voigtlander 50mm f2.5 Color-Skopar is excellent and cheap at $350 or so. The Konica 50mm f2 and the Zeiss 50mm f2 Planar are both great lenses for a little more money used.

 

[mdarnton]

Yes. There's a shim between the elements that is adjusted to change the focal length, and a second shim between the lens head and the mount to -re-adjust the focus once you've altered the FL. If you change only the second, you will just move the mis-focus to another range. You have to change them both. In order to do that, though, you have to understand the problem, and what you are attempting to do. If you're not real geeky, I doubt you can handle it. Most people don't seem to understand the problem at all.

I just remembered where I read the relevant info: http://pentax-manuals.com/repairs/j9collim.pdf

 

[crispy12]

Alright, thanks a lot! I'll study that PDF. It'll be a good project to learn about lens construction anyway. I'm getting a used M8 next month, I think I'll probably hold it off till then. I've bulk loading short baby rolls of 5 frames to test the lens so far!

 

[randomm]

I've attempted to shim two and have only been successful to get them focus correctly between 1.5m - inf. Anything closer seems to be a nono, and for that purpose I set the focus on my other one at 0.8m (fixed focus and aperture at f2). It's a hassle to carry two lenses instead of just one though...