Shimming the Jupiter 8

[boojum]

This may sound crazy, maybe it is. But some Jupiter 8's need to be shimmed to move them far enough, ~1.5mm I believe, further from the camera in order to focus correctly. So, pinhead idea, why not place shims between the LTM > bayonet adapter and the lens to make the adjustment? I have an M240 with the Epson VF so I can focus RF and then through the lens and take a photo each way. Check the focus, shim accordingly until the RF and the visual through the VF agree and I am done.

OK, guys, it sounds like it would work. What do you think? I may just try it.

 

[santino]

But why? As far as I know you shim an optical block not the whole lens body. The rf would be off because of the shimming... or am I wrong?

 

[retinax]

No, wouldn't disturb RF focusing, but also wouldn't help. It would just keep it from focusing to infinity (or could keep it from focusing past infinity). On a 50, the RF cam and optical block move in unison. Moving both if them further away from the film is called focusing, it doesn't alter their relationship. You want to move the lens block in relation to the RF cam. It's not hard on the j 8. 1.5 mm sounds excessive, mine needed something like 0.2 mm.

 

[Horatio]

I tried that with a paper shim on my Jupiter 3. Didn’t help.

 

[peterm1]

No, wouldn't disturb RF focusing, but also wouldn't help. It would just keep it from focusing to infinity (or could keep it from focusing past infinity). On a 50, the RF cam and optical block move in unison. Moving both if them further away from the film is called focusing, it doesn't alter their relationship. You want to move the lens block in relation to the RF cam. It's not hard on the j 8. 1.5 mm sounds excessive, mine needed something like 0.2 mm.

I think this is right. Its the optical block that must be moved not the rangefinder cam . (i.e. the relationship between the optical block and the rangefinder cam needs to change because the calibration between the two is off.) Shimming it in the manner proposed by the OP would change both the optical block and rangefinder cam (in unison) in relation to the camera body not in relation to each other.
I find the easiest way to think about this is by considering what happens at infinity assuming there is a hard stop (to make this hypothetical visualization easier). In this case if the lens needs shimming, presumably this is because when the focus cam is at the infinity hard stop the optical block is actually focusing beyond infinity. You need to leave the focus cam so it is still at infinity / hard stop (so the rangefinder is registering correctly) but move the optical block further out to shift focus backward to till it corresponds with actual infinity and also corresponds with what the rangefinder cam is telling the camera. This should then result in all intermediate distances also focusing correctly.

 

[former member]

If you have the earlier J-8, the type that the optics do not rotate as you focus, the easiest way to correct back-focus is to built up the RF cam using tape. I use copper tape, about 0.08mm per layer. Usually one layer does the trick. Done this way- no need to re-index the aperture ring. Best done when using the lens on an M-Mount adapter, put the adapter on first, then mount the lens on the camera. That was the RF cam stayes in contact with the tape while mounting, does not move past the edge.

 

[boojum]

If you have the earlier J-8, the type that the optics do not rotate as you focus, the easiest way to correct back-focus is to built up the RF cam using tape. I use copper tape, about 0.08mm per layer. Usually one layer does the trick. Done this way- no need to re-index the aperture ring. Best done when using the lens on an M-Mount adapter, put the adapter on first, then mount the lens on the camera. That was the RF cam stayes in contact with the tape while mounting, does not move past the edge.

I guess I know why you are called "Sonnar Brian." ;o)

My J-8 is a '55 which makes it an early one. I just did some test shots and it seems this one focuses fine. I was lax previously. I like the lens as it has a slight pastel effect when on my M-9. I'll check it on a CMOS to see if it is the sensor or the lens.

Thanks for the advice. I have it filed away.

 

[peterm1]

If you have the earlier J-8, the type that the optics do not rotate as you focus, the easiest way to correct back-focus is to built up the RF cam using tape. I use copper tape, about 0.08mm per layer. Usually one layer does the trick. Done this way- no need to re-index the aperture ring. Best done when using the lens on an M-Mount adapter, put the adapter on first, then mount the lens on the camera. That was the RF cam stayes in contact with the tape while mounting, does not move past the edge.

I can see why that may well work -up to a point. It would not however change the actual focus point, which means in this case that the closest actual focus point might be (say) 2 meters in practice not 1 meter (or whatever is marked on the lens distance scale). And if it comes to that the distance scale would be wrong throughout the range too. Subject to that if focusing by rangefinder you should be able to calibrate it to focus correctly using that method. (I think!!!!!)

 

[former member]

The distance scale is also calibrated to the Zeiss Standard. It will never be exact.

I have a test target setup that is 5m out. I put the lens on a Canon III and check the distance using the rangefinder and distance scale, get fairly close to 5m. I use a TTL viewer to focus the J-3 or J-8 on the target, note the distance, most of the time it comes up at 4.2m. You can increase the shim of the lens until actual focus through the TTL viewer is 5m, OR you can build up the RF cam until the rangefinder measures 5m. Changing the shim of the lens requires re-indexing the Aperture ring, easy on a J-8- the set screws usually are outside the focus mount. On the J-3, they are usually inside the mount- meaning you need to carefully drill out taps so the set screws fit flush.

Sometimes - especially on a J-8- the RF cam is off. The 5m target comes up at 7m, meaning the lens will not focus to infinity. For the J-8- I build up the cam until it measures 5m, then shim the lens. On a J-3, you can fix this by screwing the helical deeper into the mount. That is tedious.

 

[Andrea Taurisano]

Probably a stupid question, sorry for that: Do back-focusing Jupiter lenses back-focus so much that it's just as noticeable on analog M cameras as on digital cameras? Or is the problem mostly visible on digital images?

 

[former member]

There is a lot of variation among individual lenses. Most J-8's, you will not notice "too Much" on a film camera. J-3, most are noticeable. Some are awful, others are spot-on.
I've seen some lenses that required a lot of work.

My notes from a Valdai J-3,

Good news, the lens is in mint condition, has never been opened, and the glass looks good.


Bad news:
1) The optics module was glued into place. NEVER force one out, the guide pins will snap. I learned that from someone else.
2) The actual focus was off by 2 meters at 5 meters when using the RF for focus. You cannot use the distance scale, either. You can use a mirrorless camera.
3) The lens does not focus to infinity, the helical is not deep enough in the helical to focus to infinity.
4) Distance scale is way off, 5m test target comes at almost 7m. This is a function of the helical not being screwed far enough into the mount.