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12-28-2013, 11:08 PM   #1
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Can a lens Auto Focus be "slightly" broken?

I have a Pentax-F 35-135, and I wonder if it's slightly broken. One symptom is the manual focus. It's not smooth when turned. I have a similar 28-80 F-SMC that turns very smoothly from either the barrel, or the narrow focus ring. The lens, the 35-135 that is, focuses quickly and accurately outdoors, but inside it hunts and rarely finds an in focus point. Sometimes I'll take it out of Autofocus, move the focus manually, then put it back to Autofocus. Sometimes it can find the mark after that. I wonder if the internal gears (if it has gears) are slightly worn out by manually focusing it while the camera was in "Auto Focus".

Can lenses like this be damaged by focusing them while they are in Autofocus? I recently got the lens, and don't have any history on it.

12-28-2013, 11:52 PM   #2
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It is generally not recommended to manually focus a screwdrive lens while the camera is in AF mode. Turning the focus ring turns everything including the camera motor.

But I doubt that`s the problem. The F 35-135 is a slow lens and tends to hunt in low light. I think the issue is just the lack of light.
12-29-2013, 12:28 AM   #3
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What about the roughness in the turning of the focus? I can't believe it was like that when it was new.
12-29-2013, 12:52 AM   #4
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It is rough when in manual focus?

What about when not on the camera?

Mine is smooth, at least smooth for F series.

12-29-2013, 01:34 AM   #5
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QuoteOriginally posted by Tighelander Quote
What about the roughness in the turning of the focus? I can't believe it was like that when it was new.
I assuming roughness you feel is when you try to focus manually?
12-29-2013, 01:36 AM   #6
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The motion of the focus is inconsistent. Just now I turned it a few times and it was perfectly smooth (I momentarily thought I picked up my 28-80), then something jammed it up a little. A few mores turns, and it went back to smooth briefly. This is off the camera.
12-29-2013, 02:12 AM   #7
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Had something similar with fa 50. Screw was loose inside
12-29-2013, 02:43 AM   #8
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Lovely. Well I knew that something was wrong.

12-29-2013, 07:28 AM   #9
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Agree with something loose. Had a lens that would jam occasionally finally took it apart and found a chunk of black plastic inside. It would catch in the helicoid when the lens was held a certain way.

Recommend you send it off to Eric if you are in the states.
12-29-2013, 10:02 AM   #10
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QuoteOriginally posted by i83N Quote
Had something similar with fa 50. Screw was loose inside
I had the same issue with the FA31Ltd after it came back from repair. Depending on the angle I could turn the focusing ring all the way or only partially; camera had the same issue with it.

Repair center fixed what they broke at no costs.
01-17-2014, 03:12 AM   #11
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Well I'll be...
I was just dickin' around with the 35-135mm lens...jabbing, poking, and prying the focus ring just for the hell of it,
and it freed up what ever was causing the focus to jam 60% of the time. The auto focus is connecting more frequently.

I am happy.
01-17-2014, 05:24 PM - 1 Like   #12
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QuoteOriginally posted by Tighelander Quote
Well I'll be...
I was just dickin' around with the 35-135mm lens...jabbing, poking, and prying the focus ring just for the hell of it,
and it freed up what ever was causing the focus to jam 60% of the time. The auto focus is connecting more frequently.

I am happy.
That's good to hear, but I'd be a little concerned that whatever caused the problem is still floating around in there.
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