Shimming a Jupiter-3

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How does one go about shimming a J-3 for Leica? I have a 1961 example, which I rather like, but there is the nagging feeling that it isn't set up right for my IIIf or M2. I tend to use it for closer shots at wide apertures simply because it's fast and has rather nice bokeh. However, I sometimes wonder if it isn't acheiving as much sharpness as it could.

I can operate a very small screwdriver and use fine tweezers, and I can work metal and other materials, so I don't feel that shimming is something that I need avoid. I'm just not sure what actually gets shimmed - is the idea to move the whole optical assembly such that it is in a slightly different position with respect to the rangefinder cam? Or does it have to do with changing the distance between the front and rear parts of the optical assembly? Are there any disadvantages to consider?
 
Thanks, Brian. I may have a usable SLR focussing screen soon - a Nikon EM is on its way to me, which I bought for the attached lens. I'll never use the camera (auto exposure), and wasn't sure if it was worth the effort of selling it, so maybe the screen can be harvested for this sort of thing.

There's something I'm not clear on. Am I right in thjnking that the stand-off ring used to make fine adjustments, while shims are for gross adjustments? You mention using a 3mm shim, but also mention having 0.1mm shims. Is it the case that there must be some sort of shim between the stand-off ring and whatever it bears against, but the shim isn't actually used for the final setting?

Regarding the lens in question, it is pretty close on my Leicas. Infinity is out by a tiny amount (lamp post about 300m away), and close focus isn't a million miles off, so it doesn't seem to be a wrong-un. If fine adjustment can be done with the stand-off ring, is that all I need concern myself with? (Assuming it isn't at the wrong end of its limit of travel.)
 
A follow-up...

The screen came out of the Nikon EM easily - unscrew a little bracket, and remove the screen from the bracket.

My test focus point was a little over 1.2m away. With the rangefinder patch aligned, the focus index mark landed about one third of the way between the 1.2 and 1.5m marks (nearer 1.2m). On the focus screen, the same point was sharp (ie, lined up in the split image part of the screen) closer to 1.2m - having the 1.2m mark mid-way between the f2 and f2.8 engravings on the depth of field scale was good.

The end-stop ring was a bit hard to get moving at first, but was fine after a couple of attempts to adjust. With the final adjustment, the correlation was at the 'very hard to tell a difference' stage, and I decided that this was enough of an improvement to stop at that. I have not adjusted the aperture collar yet - at wide open, the indicator shows 'stopped down a little from f2'. I'm shooting all day tomorrow, and I don't want to attempt too much tonight - a temporary index mark will suffice for now.

While I had it apart, I used a thread pitch guage to measure the thread that the end-stop ring runs on - it is 0.5mm, which means that 1/5th of a turn gives an adjustment of 0.1mm, etc. Judging by where the aperture ring now ends up when wide open (was very close before), I reckon 1/10th of a turn made the difference on my lens - a change of about 0.05mm.

I had one mishap - one of the grub screws broke when I went to tighten it up. One of semicircular halves at the slot snapped off (first time I've ever broken a camera/lens screw). Unfortunately, the screw was still proud of the end-stop ring (the bottom of the slot was flush with it, or a smidge above), and I couldn't screw the optical module back in. Luckily, I was able to remove the screw, and make do with the remaining one. No apparent issue with the operation of the lens. If I ever manage to find a replacment, I'll fit it.

Overall, I'd say focus at this distance was out by around 3". It's hard to be exact because the focus scale isn't linear, but that seems like a reasonable estimate. The proof of the pudding is in the shooting wide open and up close, of course, and I'll be using a roll of Adox CHS 25 tomorrow to see how it goes.
 
It sounbds like you got it right. The set screws break easily. I've taken apart junk lenses to get a few spares. Two screws for the aperture ring work nicely. 0.05mm makea a big difference for exact focus.

Report back with the results on film.
 
Some test shots with the shimmed Jupter-3. Camera was my Leica IIIf, film was Adox CHS 25 developed in HC-110. Scans were done at 2400dpi, 16-bit greyscale. No scanner tricks like sharpening, other than letting the scanner set exposure. No processing in Photoshop, other than a resize or crop as required, and reducing bit depth to 8-bit to allow saving as normal jpegs, with compression set to keep the file size under 170KB.

The focus point was the little stub of a thin branch in the middle of the frame. The subject distance was about 4 feet / 1.2m. The shots were hand held in good light, and were shot at f1.5, f2, and f2.8, in the order shown. If I remember correctly, starting shutter speed was 1/1000, so 1/500 for the next, and 1/200 for the last.

Full frame shots in this post, crops in the next.


f1.5
img001_full.jpg


f2
img002_full.jpg


f2.8
img003_full.jpg
 
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