| Author |
Message |
    
Matthew Padden
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 14, 2004 - 04:41 pm: | 
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Hi folks,
I have a Pentacon 4/200 lens that seems to be stuck at a focus of about 10cm. If I turn the focus ring the lens barrel extends and retracts as expected, but there's no change in the image as seen through the lens. Aperture ring and leaves seem to be fine. Can anyone shed any light [sic]?
Thanks in advance for any advice.
Matt
Glasgow, UK |
Jan Dvorak
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, January 14, 2004 - 07:24 pm: |
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Matt,
If the lens extends and retracts as it should (and is otherwise in original condition), I don't see a reason why it would not focus past 10cm. As a matter of fact, the minimum focusing distance of this lens should be about 2 to 2.5 meters. That leads me to believe that the lens was tampered with and not put together properly. I am assuming that this is a lens in an M-42 thread mount or Praktica bayonet mount - are you using it on the proper body?
Good luck,
Jan |
Matthew Padden
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 15, 2004 - 03:08 am: |
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Hi Jan,
Thanks for your thoughts. All my tests have been done with the lens off the camera. The lens does mate to the M-42 thread on my Zenit EM camera. There are no obvious signs of tampering or forced entry to the lens, and no suggestion of anything loose inside. The aperture leaves open and close normally as the aperture ring is turned, and the aperture limiter is also working (lifting the aperture ring allows the usable aperture range to be restricted), but the focus ring has no effect apart from to extend/retract the barrel. I agree that the current focussing distance is far shorter than would be expected.
Many thanks in advance for any advice
Matt
Glasgow, UK |
Jan Dvorak
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 15, 2004 - 10:51 am: |
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Matt,
Some more thoughts:
1) Front or rear lens elements re-installed the wrong way round.
2) Don't be offended by this - an extension tube or close-up lens attached to the lens. I am assuming that other lenses focus correctly on this camera.
Other than that, I am stumped.
All the best,
Jan
Vancouver, BC |
Matthew Padden
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 15, 2004 - 02:49 pm: |
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Hi Jan,
Oops; guess I owe myself a big 'duh'... I was doing all these tests with the lens OFF the camera. With the lens ON the camera, the focus works fine. Saves me worrying about opening the lens up at least.
Matt
Glasgow, UK |
Jan Dvorak
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 15, 2004 - 04:02 pm: |
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Matt,
An obvious question pops to mind: If you tested the lens OFF the camera, how did you know that the closest focusing distance was 10mm?
All the best,
Jan |
Matthew Padden
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, January 17, 2004 - 04:10 am: |
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Hi Jan,
My 10cm figure was estimated by measuring from the front of the lens to the nearest clearly focussed object. Not exactly scientific or even accurate.
Matt |
