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Auto forces issue with my 2nd contax n24-85

 
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chhchow



Joined: 20 Jan 2012
Posts: 5

PostPosted: Fri Jan 20, 2012 12:57 pm    Post subject: Auto forces issue with my 2nd contax n24-85 Reply with quote

I recently bought a Contax n24-85 (EOS converted by conurus in 2010, the SN: 12705046) but the auto-focus seems not really functioning with my Canon 5D2 no matter indoor, outdoor, day and night. When I half-press the shutter button, I can see the lens is “trying to seek” the focus point but fail. It keep looping to search that I cannot press the shutter. It is not help even I put the 580EX2 for assistance. The only think I can do is switch it to MF (F22) and adjust by myself for photo shooting. Could you please give me some hits or tips what thing I should check before return to the seller? The firmware of my 5D2 is 2.1.1 and I change the focusing panel to Eg-D, does it affected? Please help
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conurus
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Joined: 15 Aug 2006
Posts: 795
Location: Vancouver, Canada

PostPosted: Sat Jan 21, 2012 5:25 am    Post subject: Reply with quote

Thank you very much for your question.

First, if you have a different lens you can try on your 5D2, that would narrow down if it is a problem with the lens or the camera body.

Even though every lens we converted is tested at least 4 times before and after conversion before it is shipped, a lot of things may happen after the lens is shipped. Are you getting sharp results if you use manual focus? A lens which has been subject to impact or abuse or has been tampered by an inexperienced camera repair technician and which as a result suffers from an optical misalignment problem may fail to lock on using autofocus, but you can rule out that possibility if the lens is sharp wide open when you use manual focus.

The focusing screen has no effect on autofocus. The autofocus sensor is situated at the bottom of the mirror box.

Summary:

1, is the camera body autofocusing properly with a different lens?
2, did you get sharp results shooting wide open using manual focusing?
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chhchow



Joined: 20 Jan 2012
Posts: 5

PostPosted: Sat Jan 21, 2012 7:14 am    Post subject: Reply with quote

thanks for your reply

i tried with diferent lens like 35L 16-35 s85.4 and 70-200IS with my body and there is no similar issue, i get the sharp results if i used manual focus. Actually, when i use AF and half press the shutter , i can see the lens is "trying to find" the clearest point but it just keep looping. So i guess that is not an issue with the lens motor

i put this lens to another 5D2 (with firmware 2.0. 8 ) and the lens work perfectly fine. (mine one is 2.1.1 i just bought recently) It is strange....

And the seller told me this lens was worked fine with his 5d2, 1d4 and 40d with no such issue
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chhchow



Joined: 20 Jan 2012
Posts: 5

PostPosted: Sat Jan 21, 2012 7:52 am    Post subject: Reply with quote

i got the previous 5d2 firmware and downgrade my body either 2.0.9 , 2.0.8 or 2.0.3 but the problem is still...
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conurus
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Joined: 15 Aug 2006
Posts: 795
Location: Vancouver, Canada

PostPosted: Tue Jan 24, 2012 3:02 am    Post subject: Reply with quote

This is very strange indeed.

  • If the lens tries to autofocus, that means the ultrasonic motor is working fine.
  • If the lens is sharp wide open using manual focus, that means it is free of optical aberrations which would interfere with the camera body's AF operation.
  • If the lens works fine on a second 5D2 body, that is even stronger evidence that the lens itself is working.
  • It has nothing to do with firmware version of the camera, that I am pretty sure.

Well I really have no idea. If you could return it back to the seller, that would be great. If you can't, selling it may be a good idea, since it is very likely that only one camera body on earth is not working with it properly. As for why... I really don't know...

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reeray



Joined: 24 Dec 2011
Posts: 12
Location: Thailand

PostPosted: Tue Jan 31, 2012 7:08 am    Post subject: Reply with quote

Two things you might like to check.

Switch the AF point to the centre, (one only) mark.

Check in the micro adjustments menu that it is set to zero.

If this fails then I too am at a loss with the problem.
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chhchow



Joined: 20 Jan 2012
Posts: 5

PostPosted: Tue Jan 31, 2012 7:41 am    Post subject: Reply with quote

Finally I discovered the problem of the Lens: it seems like the aperture of the lens cannot open it smoothly after turning to F22. I remembered last time when I switched to F22 and test, then I roll it back to F3.5, I found that the aperture of the lens itself is still in F22, that's why the auto-focus is not working. Then I press the “pre-shoot” (the button in the front button and next to the Lens rang) several times and lucky the aperture back to normal that can use the auto focus again. And this problem is happen arbitrarily and the temporary solution is press the “pre-shoot” button until it back to normal. Does it harmful? Any ideas?

And the bad thing is, my seller refuse to refund after he known the issue and he suspected I am the person who break this lens…..Although I found this issue within same day (actually less than 2 hours) I guess this is the reason why he selling to me. Anyway, may I know will it be able to solve this issue if I send this lens to you regards on this problem? And how much does it cost? It would be nice if you can review and resolve this issue while you are in Hong Kong this year that would be great ^^ Again, many thanks for your help
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reeray



Joined: 24 Dec 2011
Posts: 12
Location: Thailand

PostPosted: Tue Jan 31, 2012 8:01 am    Post subject: Reply with quote

The control of the aperture is via the camera and not the lens aperture ring.This may be what is confusing you. If you look at the lens aperture whilst adjusting FROM THE CAMERA you should see the changes.
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chhchow



Joined: 20 Jan 2012
Posts: 5

PostPosted: Tue Jan 31, 2012 3:19 pm    Post subject: Reply with quote

Thanks for you comments and what I discover is the aperture will stay F3.5while AF is on and only Change the aperture while I press the shutter, however the problem is when I turn the lens ring to F22(manual focus) and adjust to F22 via 5d2, that's fine for this photo. Then I turn the lens ring to different (like F3.5-F16 whatever) the aperture cannot on the lens cannot back to AF, it just keep in the smallest aperture F22, Since it is the smallest aperture, then the AF is not working and I saw the motor is keep "searching" the object
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conurus
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Joined: 15 Aug 2006
Posts: 795
Location: Vancouver, Canada

PostPosted: Tue Jan 31, 2012 6:38 pm    Post subject: Reply with quote

Hi chhchow,

Yep, you have figured out the problem! The electronic aperture of your lens is broken and the lens keeps on searching for focus because AF only works properly when the lens' aperture is wide open.

Only Contax Japan will be able to fix the electronic aperture. (More specifically, it is the flex cable going to the electronic aperture that is broken, not the electromagnetic diaphragm itself.) The cost is approx 25,000 yen, subject to their final repair estimate.

Do not just find some repair shop to fix this problem. The repair requires a special flex cable part that only Contax Japan has. An independent repair technician will do some band-aid fix for cheap but that won't last long.

Your seller is clearly at fault in this case. You discovered the problem on the very same day, but he still refuses to refund and accuses you of breaking the lens. This is totally unreasonable and unacceptable.

I have seen this problem a few times. From my statistics, approximately 1-2% of 24-85 lenses will eventually develop an electronic aperture diaphragm problem.

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