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01-19-2012, 12:27 PM   #1
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Wobbly focus ring on DA 35mm f2.4

Hi,

I have a question about this lens. I've just bought it used from fleebay and as soon as I took the first picture I realised there's something wrong with it. It appears that it suffers from some back focusing, but I also noticed that the focus ring is actually a bit wobbly. Not that it's loose, but there definitely is some movement. The easiest way to determine the wobbliness is to try to very gently turn the ring with the focus switch on the camera in the AF position. The resistance from the focus motor becomes obvious, but the ring still turns in that position, not more than a millimetre, but it does turn which affects the focus point. Here's an example.

With focus confirmed by the camera (focus point in red) and with obvious back focus



and after this slight turn that I've just described




The camera was on my table and photos were taken seconds from each other the only difference being that I manually turned the focus ring until I felt the resistance from the focus motor.

The shift of focus point is obvious, moving it closer to the actual focus point. This certainly can't be normal behaviour and I was wondering if anyone has ever had similar experience? Maybe someone would be willing to check their lens and report back. is there anyway to deal with BF? My camera is the trusty old K10.

01-19-2012, 03:06 PM   #2
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Since you just got it, you would probably be best off to return it and try another copy, perhaps from another seller. You shouldn't have to deal with that with a new lens.
01-19-2012, 03:25 PM   #3
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you got a dud, that's why it's on ebay
01-20-2012, 11:25 AM   #4
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Looks like it's not a dud after all. Here's an unscientific test with batteries. Camera on the table, MLU On, just changed focus points from left to right. Here's the result.














Now I'm baffled. How come it locked on batteries spot on, but failed on those pictures in the first post? Lack of contrast?

01-20-2012, 11:45 AM   #5
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QuoteOriginally posted by deepbluish Quote
How come it locked on batteries spot on, but failed on those pictures in the first post?
Disregarding the physical wobbliness
and any issues connected with it,
the repeated lines of the corduroy fabric
might have confused the phase detection focussing.

I would have had trouble
manually trying to focus a rangefinder
on that kind of subject.
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