Early Kiev/Contax Mount Jupiter-12 - different optics?


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5:07 AM
Dec 24, 2022
Recently I acquired a 1958 KMZ made Kiev/Contax mount Jupiter-12. It has bare aluminum body, blueish coatings, and rear element with metal protection ring/collar - somewhat like the original prewar Biogons. This design seem to be dropped at around 62/63 when manufacturing of J-12s moved to LZOS factory. Later J-12s has bare glass rear element with painted sides, just like all LTM versions.

Anyone knows if there's difference optically in the early Kiev mount KMZ J-12s from the later ones? Maybe some side by side comparison will be nice.

My guess: To convert the original Biogon design to use on LTM bodies, the diameter of the rear element has to be reduced a bit in order to avoid interference with the focus cam, thus the reshaped rear elements. However the change seen on later Kiev mount J-12 lenses might be purely economical consideration...

My copy of KMZ J-12:

Based on the fact the Soviets standardised all their lenses in such a way that the "LTM" lenses were basically Contax lenses with an M39 screw mount on the back, it wouldn't surprise me if they also standardised the Jupiter 12 in the same way.

It seemed like they wanted one production line for the optical elements so that those parts could be fitted into Contax or "LTM" mounts depending on what was needed that day, so it stands to reason that when they ran out of the German-made components for the Biogon, they'd make one standard set of Jupiter 12 elements that would work for both mounts.
And here's where I get to use "Why couldn't they just let Biogons be Biogons".

KMZ seemed to do that for their J-12 in LTM. My 1952 KMZ J-12 in LTM compared with the Biogon "T"- rear elements have (as close as I could measure) the same diameter. The Biogon and Contax/Kiev 1956 J-12 both have the metal collar for the rear group, The rear element is held in place with the metal ring. On the LTM lens it is cemented in place. I believe the formula is the same, just the LTM version could not accommodate the extra thickness of the collar.

Biogon and 1956 KMZ J-12 in Contax/Kiev mount.

1960 J-12 compared with the 1952 J-12. Different formula.

The optics on the LZOS J-12 are different from the KMZ J-12. Most likely the supply of Schott glass ran out, requiring a change. This does not answer whether the last of the KMZ J-12 lenses also changed formula, similar to the Jupiter-3. From sometime in 1954 through 1956 KMZ produced two versions of the J-3, one with the remaining Schott glass and the v2 with Russian glass. The performance of the second version is not as good. Probably the reason that KMZ turned it over to another company to make. I would guess the same is true of the J-12.
Not all the CZJ Biogons in LTM are the same, differences drive me crazy. Two 271 series lenses with metal rings around the rear group, followed by 284 series and 311 series. The prewar Biogons that I have in Contax RF mount have metal rings around rear group similar to pic in first post.
I remember one of those LTM J-12's with the collar jamming up on the RF Follower of my Canon III. The J-12 went through a quick evolution.
The first lens, serial number 2712841, will not mount on my Leica IIIc stepper or Leica IIc, but will fit on Canon 4sb and other screw mount Canons, my Tower (Nicca) cameras and Leotax F. It is a matching numbers lens, I have had it apart. Not sure what it was supposed to have fit, given that the IIIc stepper would have been a common camera in use at the time the lens was made.
Didn’t realize there were so many variations during a short period of time. The KMZ Kiev mount J-12s’ rear collar seem to be direct copy from post war Jena Biogons which were slightly reduced in size compared to pre war Biogons.