KMZ maintained production of the J-8 in thread mount for the full run, and in my experience- they made the best of the lenses of the USSR. When you find one with markings in English- means they made it for export. The 1975 J-8 was made for export, and is one of the best I've used. KMZ manufactured the Jupiter-3 only until 1956. I have a Valdai J-3 and ZOMZ J-3 that match my 1956 KMZ J-3, but I went through a lot of J-3's to cherry pick them. I'm never had a bad KMZ lens. But- I did have to put a lot of work into my two 1950 KMZ J-3's, figure they were assembly practice for the new fixtures.
And- my favorite lenses are the ones that I CLA'd and/or repaired myself. Using a lens and having the focus spot-on as a result of your hard work is very gratifying.
Hi Brian, I have had a question in my head for a while and this seems a good thread for it. You say that KMZ were in continuous J8 production for its whole life but do you have any information on reformulation of the glass/spacings during this period. From you experience is it "safe" to replace a scratched KMZ 57 front element with a good 75, 80 or even 92 KMZ one. Obviously whole optical unit's can be swapped easily but can single elements? Taking this further, are Arsenal glasses compatible with KMZ? I suppose not but....
I've tried this with J-8's before: at some point the front elements increased in diameter. I did not record the dates, but tried replacing the front element from a mid 1950s lens with a newer one, did not fit. The Jupiter-3 is a different story: I've replaced front elements of 1950s J-3's with those made in the 1980s. The rear triplet of the J-3 changed formulation and the mechanical fixture changed when production passed from KMZ. You can swap out KMZ elements with CZJ 5cm F1.5 elements- work fine. You cannot use the later optics.
I have a large number of parts J-8's and J-3's, when i get a break- will take some measurements.
These are "Triple-Zero" screws. I use a hand drill with a triple-zero drill bit to get them out.
Sometimes you can use the tip of a flat head screwdriver and nudge it out. Turn the aperture ring against the screw to put some friction on it. Then slowly back the screw out if one side of the head is remaining. Sometimes a small slot remains, will also work. Then use a magnetized screwdriver to get it out.
This is the worst part of working on a Jupiter lens, the screws are fragile. Next up is cross-threaded retaining rings.
Hi Brian, as it's on topic I have another question that may be of value to the OP. For J8s is there still some value in shortening the distance between the central and rear element block (I think I saw a figure of 0.4mm mentioned for J3s) or does sample variation make this unwise?
Sample variation exists, and I only suggest doing this for lenses that are first shimmed for close-up/wide-open work but do not give an acceptable focus at infinity when closed down 1-stop or so. This condition indicates the focal length of the lens is on the long side of the range. The deviation for the J-8 and J-3 is 52.4mm+/-1%. Get luckym get a lens on the short side of the deviation - the lens will focus correctly across range. In the middle- optimize for wide-open/close-up, 1-stop gives good infinity. "The Far Side"- get out your Lab coat, chase an Ice Cream Truck, and move the rear group in to shorten the focal length. You will need to reduce the main shim to compensate. I computed "roughly" 1mm ~ 2mm is required to bring the focal length into good agreement. You will be limited by the thickness of the main shim.