CZJ Biotar in M42 mount, 1949

dexdog

dexdog

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I recently picked up this lens cheap, seller was advertising it for parts or repair. A couple of the rear elements were very hazy, but cleaned up nicely once I took the glass out. I have a question for the lens geeks. Close focus of 0.9 meter seems spot on, a measured 5 meter spot in my house shows 6 meters on focus scale, while infinity focus seems way too short at about 50 meters (areas farther away than 50 meters will not come into sharp focus at all). Any suggestions on where to begin? I am not likely to use infinity focus too often, but would be nice
 
My uneducated guess is that the lens assembly has been taken out of the barrel threads and when it was threaded back, it is not threaded in the correct way.

But let's see what others, more knowledgeable members think.
 
Typically- if the helical is misthreaded the focus is off by much more than what you are seeing. The individual elements and groups being out of position, or a barrel not being properly shimmed could be the problem.

When putting the rear elements back in: is there the possibility that they went in too far? Or the front elements not far enough?

Try unscrewing the rear section about 1 turn and see what happens.
 
Sonnar Brian said:
When putting the rear elements back in: is there the possibility that they went in too far? Or the front elements not far enough?

Try unscrewing the rear section about 1 turn and see what happens.
Click to expand...
From what I have seen on youtube, the rear lens group is press-fit into the lens barrel, a retaining ring holds it in place (i.e., there are no threads to adjust how deep it is seated). The front lens group appears to be seated properly, it is press-fit as well and held in place by retaining ring like rear group. I think I will start by making a shim to go under the rear lens group fixture, will start with card stock or aluminum tape.
Thanks for the ideas!
 
I removed the rear lens group and inserted a shim made from an index card. The shim is 0.24mm thick. Anyway, it worked very well, infinity focus is now about 210 meters or a bit farther, good enough! The attached pic is an 8x center crop using one of my lens testing subjects, a STOP sign at a known 210 meters from my front porch. Gray and rainy this morning, but I think the shot looks decent. Maybe not quite as sharp as some of my Sonnars or J-3s, but pretty good for wide open at f2. Adding the shim improved the performance significantly, makes me wonder whether the shim had been removed at some point in the past, or whether it was never shimmed in the first place. Close focus still good, and my indoor benchmark of a measured 5 meters now shows up at 5 meters on focus scale insteada 6.
 
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I took a couple hours this morning to tear down the black Biotar seen in the first post in this thread. Focus and aperture almost immovable due to old grease, a truly grimy mess. I dont think that anyone had been inside this lens since it left the Zeiss factory in 1949. The process to disassemble helical is not that different from an LTM Jupiter 3 or LTM Sonnar. Got the lens back together (took me 3 tries to get the correct start on the helical), the lens works very smoothly now. I decided to compare the black Biotar to the nickel-plated version also made in 1949 that was attached to my Contax S.

I was surpised to find out that the chrome version was set up similar to the black version, i.e., infinity focus was about 50 meters, no shims under rear element. Did I get two oddball lenses or did CZJ set these lenses up to max out at 50 meters? Anyone spot a lens box in this picture?
 
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Nice job!
Have you verified the focus discrepancy on film? I noticed that sometimes the sensor stack can induce odd focus behaviors. I have had this even with new lenses which were calibrated for digital Leicas instead of film ones.

I am asking because I have a silver Biotar and a black one, both very close to your serial #s, and they focus fine on my M42 Fujica.

And yeah I spot the Jupiter3+ box, which I am so glad I picked up for when they were still sold (and.. well not cheap... reasonably priced?).. I sometimes wish I had picked up another just so I could use the brass focus mount of it.
 
TenEleven, the black Biotar is 3188990. I have not verified focus on film because my Contax S has a broken shutter and I do not have another M42 camera. I will have to order an M42 to Nikon Z adapter to try both lenses on my Nikon Z6 to see if I get the same results. Thanks for the idea! So far, I have only shimmed the black lens, have not done anything to the silver one.

Note: test pictures on Sony a7iii.
 
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Are you certain that the problem is not the adapter?
Also- 50m at infinity, at what F-Stop? Focus shift is a feature, "not a flaw"... If it close-focuses at F2, then F5.6 will shift the focus to infinity.
 
Also again, film vs digital. In film you have to hit the silver halilide (or other particles) suspended in the emulsion which has a certain depth to it, so there is a certain amount of focus "leeway" built into the medium. In a digital camera you have to hit the micro lens above the imaging (photon) well pretty much exactly or it won't look sharp. This is by the way one of the reasons digital lenses are so large - it's optically a very hard problem to solve while making sure that the incoming rays also hit the sensor in a perpendicular fashion, but I digress...

I have noticed this in the real world with a "focus test" Nex 5N camera which I use for repair and have modified to remove the AF linkage (so it won't hit the back of biogon and other lenses) and shimming the mount to be perfectly in focus with L39 (LTM) lenses.

However, I have found that even with the shim being perfect, for example, all Sonnar lenses read as going over infinity, whereas Tessar and Planar type lenses read spot on. I have also had certain wide angle lenses (the Ricoh GR 28mm) read as not quite reaching infinity on the digital camera but again the lens was fine when used with film - even wide open when checked at very high magnification.
 
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Sonnar Brian said:
Are you certain that the problem is not the adapter?
Also- 50m at infinity, at what F-Stop? Focus shift is a feature, "not a flaw"... If it close-focuses at F2, then F5.6 will shift the focus to infinity.
Click to expand...
Sonnar B, 50 meters is about the extent of focus at f2 with the unshimmed silver lens. Things get better as the lens is stopped down, but the 210 meter STOP sign is not in clear focus until f8; although things are a lot better by f5.6 at 210 meters, it is not quite there. Thanks for the responses from TenEleven and Sonnar B. I have a lot to learn about these lenses. Hey, at least I have a shimmed version and an un-shimmed version now! Also, the shimming is easily reversed, takes just a few minutes to remove rear lens fixture, only one retaining ring.
 
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Just tried the same STOP sign at 210 meters with the SMC Takumar at f1.4, it performs similarly to the Biotar. ie., is not in sharp focus. Focus at 210 meters gets better upon stopping down, but like the Biotar, the Takumar does not get there until f8.
 
I've polished adapters down to correct problems like this before. Since it is 2 of 2 Biotars: I suspect the adapter at this point. You can always take the shim off the rear group that you made.
 
Seconding what Brian says about the adapters, I've never had the really expensive ones but at the same time even branded ones were of questionable accuracy. I certainly would not adjust my lens according to one.

That being said, by design - most of these adapters go over infinity as to make sure that all lenses (even the slightly out of spec ones) can focus through its range. Not quite reaching infinity is rare and I haven't had that ...
 
OK, I changed adapters and both the SMC Takumar and the un-shimmed Biotar focus to infinity wide open! Sonnar B got it right, the adapter was the problem. I will remove the shim from the black Biotar. The adapters in question are cheap ones, K&F Concept, although in two different designs. The one with the shiny orange ring marked M42 to E-mount was the one that worked well. The other one marked M42 to NEX is the one that did not work, have probably had it since 2010 or so when I bought a Sony NEX-5
 
Intrigued by the results of switching adapters, I attached this heavy CZJ 25cm/6.3 Tele-Tessar on the M42 to NEX adapter and saw that the silver ring that touches the base of the M42 mount moved when I hung the lens on it.

The M42 to NEX adapter has three small set screws holding the silver ring in place. I used a 1.25mm hex wrench to tighten all three screws, and lo and behold both the un-shimmed Biotar and the SMC Takumar will both focus wide open at 210 meters. I also noticed that the adapter with the orange ring has 4 set screws insteada 3. Makes me wonder if the manufacturer recognized a problem and fixed it. Many thanks to TenEleven and Sonnar B to figure this out- you guys are great

 
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You could probably polish down the front of the adapter to allow the lens to screw in deeper, then use the set screws to re-align the focus and aperture index.
 
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