CZ 21mm Biogon on Contax IIa -- hits the innards?

[Trask]

I just received a beautiful-condition 1950's CZ 21mm Biogon and intended to put it on my Black Dial Contax IIa. I set the shutter to T so I could see just how far the lens went into the camera, and found that the little ring with ears at the rear of the lens would hit the top and bottom of the lens chamber when focussing the lens. Then I found that in fact the rear ring-with-ears rotates. Can this be correct? Can Zeiss have manufactured this lens with this ring and ears knowing that it would hit the innards of the lens chamber, then gave the ring the ability to rotate? So that at some point the ears hit the top and bottom of the lens chamber, and the lens can keep turning/focusing because the ring rotates around the rear element?

I can avoid this by putting the lens on my Nikon S2, which reportedly has larger lens chamber than does the Contax IIa. But I'd like to try the Contax, IF this is really how this is supposed to work.

Thanks, Contax experts!

[Jeff L]

I thought this lens was for this camera....
I might suggest an email to Henry Scherer at zeisscamera.com the ZI Contax specialist.
I had my IIa Blackdial serviced by him.
Good luck.

[wjlapier]

Please report back what you found. I too have this lens and have used it on my S2 ( long since sold ). I just picked up a Contax to LTM adapter and found the "ring with ears" does in fact rub around in the inside of my IIIc body. I removed the ring, but just realized it may be there to protect the rear element, but why is it shaped the way it is?

I can use the 21 on my new to me S3 2000, but I like the compactness of the IIIc and found this adapter, so I'm out today shooting a roll to see how it works.

Anyway, I'd be curious too to know why it is hitting the inside of your camera.

[Trask]

From inquiries I've made elsewhere, it seems no one has a strong answer as to why the ring-with-ears is on that lens. You will not that the ring has two red dots opposite each other, and the idea is to rotate the ring so that one of the red dots is aligned with the larger red dot on the actual lens mount -- this larger red dot being the one you line up with the dot on the body itself when you mount the lens. When all this is done, the ring-with-ears is perfectly aligned to enter the lens chamber without hitting anything. However, when the lens rotates either in mounting or when focusing the ring rotates as well, and the ears hit the top and bottom of the lens chamber. The lens then continues to rotate, with the ring-with-ears rotating on the lens. It doesn't hit on the interior of my Nikon S2.

I can only suppose that someone, for some reason, thought the ring-with-ears served some purpose, perhaps, as you say, in protecting the rear element in some fashion. It really strikes me as being something on an unnecessary "appendix" that might be removed without causing any harm. In my lens and camera, the ring-with-ears does cause a bit more drag when focussing, but it's not significant. If I felt comfortable taking it off, I probably would.

FYI, I'm sending my IIa to a repairman for a CLA, and I may ask him why he thinks the lens is built like that. It's a Zeiss mystery.

[wjlapier]

I posted a question about the ring on RFF before reading your question here. Someone replied that it acts as a lens hood for the rear element. Taking it off might cause light bouncing off the film and could cause problems. We'll see after I get my film back--I shot with the 21 Biogon on my Leica IIIc with the ring off. I could have left it on, but it did rub on something inside the IIIc when I first mounted it.

Bill

[Mark Layne]

Not sure about the Contax but on the Contarex the ears are necessary accomodate the locked up mirror then remain as a flare shield
Mark