Need help with a wrong aperture shown with my Contax Zeiss Distagon 2,8/25 AE

ddc

New Member
I own two Contax Cameras
139 and 159 MM

and four lenses:

Distagon 2,8/25 AE
Planar 1,4/50 AE
Sonnar 2,8/135 AE
Tele-Tessar 3,5/200 AE

Everything works fine except the aperture with the Contax Zeiss Distagon 2,8/25 AE.
On the lens I adjust 2,8 but the camera shows 1,4. Same is for other apertures: It is simply two apertures wrong.
· On both cameras same problem
· With all other lenses the aperture is exact
· What makes me crazy: the measuring seems to have not a big problem. If I compare Distagon 2,8/25 with other objectives and measure e.g. white wall or some other neutral object, I will get same value of exposure for the same aperture (I am reading the real aperture on the lenses) or in the worst case Distagon 2,8/25 will show half exposure longer needed.

I was thinking to disassemble the objective and move the hook to show exactly the right value on the cameras, but than, I will get the wrong value of exposure. I am totally confused! How can it be? What is wrong here? Is there any other measuring parameter I forgot?
Is it easy to move the hook/ring or do I need to put the lens all apart? From the back side, it looks to be reachable without big disassembling.

This problem occurred after my old RTS II broke down. This camera was anyhow showing wrong apertures on all objectives and I was compensating it with the ASA adjustment. Now, I bought a “new” 159 which works fine and I first now noticed the problem.


Thanx for the help
Drazen (Klagenfurt, Austria)
 

stealth

Gold CI-Patron
Hi Drazen

As you already mentioned, I think it is only the shown value, which is not correct. I had something similar on the 139 once but back then it was the camera's problem. I got it fixed and now everything is fine. The real apperture is not affected by the shown apperture as long as you see that the blades are closing and opening when you turn the ring.

Since it is only an aesthetic problem, you could leave it like this. I cannot tell you what to think of when disassembling the lens since I have never done it. I for my part would briefly ask Zeiss' Support. I have found out that they were quite good back then, when I had to contact them few years ago. Also they can tell you what it would cost to get this issue fixed.

Cheers,
Milos
 

ddc

New Member
Milos, thank you for the reply!

I am sure the camera is not the problem in my case since:

  • both cameras I have show the same problem and
  • other three lenses are working 100% fine

I am also unsure if the problem is only a cosmetic. If I turn the aparture ring on the camera (the hook positioned at approx. 1 o'clock if one looks at the opened Contax body inside), than the turning of this ring will influence the measuring values: exposure will show longer values when I turn it clockvise.

This means that, if I adjust the hook on the lens - and therefore I need to move it for two stops/aperture values, I will get for two aperture too long exposure values (additionally to already half aperture too long, but let's ignore this half at the moment).

This is confusing me!!!
In my understanding, the right adjusted aperture on my Distagon 2,8/25 (if I move the hook for 2 stops, so the camera shows the same value as on the lens) - MUST than show the right exposure values and I believe it WILL NOT. Instead this, it shows now the right values, where the aperture hook stands wrong. On other lenses everything is OK!

But maybe the measuring system works different and I don not understand the function???

Confused, confused, confused ...

Drazen
 

stealth

Gold CI-Patron
Hi Drazen

As I understand the problem is with the lens, not with the camera. Perhaps I was not clear in my last posting. :) Sorry for that.

I am not certain on how the metering with those two cameras works but I THINK that the apperture values mechanically transferred from the lens to the camera might be only important if you are in full automatic mode (P, e.g. with a Contax RX, I believe the 159 has something similar) or in semi-automatic mode (Tv). When using Av or M the camera does not need to know which aperture you have selected.

When metering, the camera will always look for the amount of light coming in, whether this is aperture 1.4 or 16 does not matter, and then set the corresponding shutter time. If you put a filter on your lens which absorbs let's say one aperture value (e.g. 4 -> 5.6), the camera still thinks that you have set aperture on 4 but in the end there comes as much light in as if you set it on 5.6. Therefore it is not important what the camera thinks. :)

I guess the best thing would be to briefly contact Zeiss and ask them if they think that this issue is something worth fixing or not. :)

Cheers,
Milos
 

ddc

New Member
Well, it is time to inform you that I have found the problem.

At 12 O’clock on the body/camera lens opening there is another small hook (I wonder how I did not see it before!) which is responsible just and only for the aperture information in the camera. It has no influence on the measurement and if you move this small hook, the exposure will not change at all.

What happened: Somebody (probably before I got the lens, the previous owner) was disassembling the small part on the lens which is fixed with two screws. This part is asymmetrical so, one can fix it other way round by mistake. In my case, this had happened and now a shorter side was moving the small hook – so, it moved the hook from zero-position (aperture in the viewfinder = 1,2) to 1,4. Now, I turned it other way round and the longer end is moving the small hook to the real value =2,8.

I am happy with this now :)
Thanks for reading and advices!

Drazen
 

rollebajo

New Member
Wrong aparture 50 mm 1,4 fix

I had the same problem with my Contax 50 mm 1,4 lens, it showed wrong value in the viewfinder. I flipped this little thing the other way around, and now everthing works OK (made me very happy!). Earlier the value shown in the viewfinder was 1,2 when lens was set on 1,4 and so on, all the way up to the smallest aparture.
Thank you very much for this help!
Roland J
 
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