Brian has had more experience of J3's than I have. However, I have yet to come across a J9 that front focussed. Some have been very close but all those that needed adjusting were back focussing. In other words the actual focal length was slightly too long for the cam action. However, Robert Ludwig's words are a little ambiguous. Furthermore, to my mind and I stress it is only my opinion, not only are there several weaknesses in his test but the results are written up in a way which many people misread.
Firstly, the test seems to be more about whether you can use an FSU body with "standard" lenses i.e. Leica, Canon and others. As far as the lenses are concerned, I don't think his tests are conclusive. He used only 23 lenses of different sorts. Not surprisingly, he found the least problem on the J12. Not only is this of moderate aperture but has a greater depth of field. In any case, as the depth of focus is less the wider the angle of the lens, the film plane/flange distance is likely to be more critical than the caming where the depth of field is more likely to cover it. He doesn't state the source of the lenses. Are these from an average FSU seller and what is their history? Have they been subjected to "kitchen" repairs or are they as they came out the factory? In the end you end up with a relatively small sample of uncertain lenses.
Next, think about the way you or most people focus an RF. Ignoring the Bessa L (which is not a rangefinder 😉 ), I doubt anybody takes a steel tape measure out to measure the distance but uses the RF. If you removed to distance scale it would have little effect on most people unless they were trying to calculate DOF or use flash. Therefore the accuracy of the engraved distance scale is not important. As he says to achieve an indicated lens distance setting you need to measure to a point behind the subject. However if you use the RF, this is not the same thing. Many people that have found focus problems and sent me messages asking for advice, first get out the tape measure because of this. Indeed I have had several messages where as far as using the RF is concerned, the lens works well and they are getting good results using the RF. However, they are worried because it doesn't match with their tape measure!
I am not an optical engineer nor am I a camera tech. I have "sorted" a number of J3's though not as many as Brian. I have done quite a few more J9's, certainly more than were "tested" in the link below. I would not call my results empirical by a long shot but I have reached several conclusions which I am happy with.
The J3's I referred to earlier probably came from a "lost" supply that had been discovered. As such they had never been sold or "allocated". Unless you can find something like that (hen's teeth), you are better off staying away from the pristine examples. They are most likely pristine for a reason. To that end, there may well have been some QC issues especially with Friday afternoon lenses. If your lens is full of Yak spit and stiff and notchy to focus, it could be a good thing. It means it is less likely someone has been tampering with it. We are talking about fractions of a mm here. If you take a J9 apart or look at the pictures in my guide, you will see that one of the helix is very coarse. Due to the way the helix has 4 start points and because there are guide slots on both sides, it is easy to put the focus mech back together 180 deg out. This will change the caming. Take it apart again, re-grease it with a different amount of grease and again the caming can change. I have seen all sorts of lube used. If all the lenses back focussed by the same amount, it would be easy to just give simple directions like take x amount off y shim. In reality I don't find this works. If it were purely due to Contax/Leica differences then they would all be out the same. I haven't found this to be the case. In general, there is a tendency for back focus issues with the J9 that becomes more apparent on the M8 and especially the RD1. However the amount varies. I believe, again purely on my experience is that the difference between the Leica and Contax focal length for the "50" lens is a red herring. It is only important if the cam is directly connected to the lens group as is the case with the Industars and most of the J8s. Once you introduce a separate helix/mech for the lens group and the cam, the design focal length of the lens does not matter. If not, you wouldn't be able the range couple lenses from 21mm up to 135mm and beyond. Both the J3 and the J9 (and one type of J8) have a separate helix for the cam. As the actual focus mech on the Contax and the LTM is so different, I can't see that the fact that the Jupiters are based on Zeiss Sonnar designs is the root cause.
Kim
Kim
