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01-23-2009, 08:05 AM   #1
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Help - intermittent autofocus probems with 50-135

I have a 50-135mm f2.8 that I has intermittent autofocus problems on my K20D. Occasionally on mounting the lens, the autofocus motor in the lens (SDM) does not actuate. The viewfinder does not show 'MF' (unless I switch the lens to 'MF'). If I unmount and remount the lens, the problem goes away.

I've also noticed that the autofocus is not as smooth as my 16-50mm. With the lens cap on, the lens will focus across the full range; the 15-60 does this very smooth, but the 50-135 is very slightly 'lumpy'. I doubt if I would have noticed this if I was not looking for problems.

I've checked the lens contacts and the look clean and functional, though I am not sure which contacts are used for what purpose.

To make matters a little more complex, I purchased a 50-135mm f2.8 from Amazon 'warehouse deals' four weeks ago. The lens is categorized as 'used', but is in the box and in its original bag, so it appears completely new, with the only issue a tear in the box. I get to return the Lens for up to 30 days, which is nearly up. I got a great deal on the lens (570 USD), so I am reluctant to return it if I don't have to. The lens did not include the warranty card, but none of my other Pentax lenses did either.

- Any suggestions?
- Is this type of problem normal with autofocus lenses, or rare?
- Is it likely to be a significant fault?
- Does anyone have a 16-50 & 50-135 that they could check to see if the motor should be the same smoothness?


I would appreciate any help!

Thanks,

Jonathan

01-23-2009, 08:58 AM   #2
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I had a problem with that same lens about a year ago. All of the sudden while shooting a wedding, the lens motor went out and it started using the camera's motor. To make a long story short, I had to send both the camera and lens to Pentax and the problem was corrected. Turns out it was something in the camera, not the lens.
01-23-2009, 10:27 AM   #3
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QuoteOriginally posted by jfsavage Quote
I have a 50-135mm f2.8 that I has intermittent autofocus problems on my K20D. Occasionally on mounting the lens, the autofocus motor in the lens (SDM) does not actuate. The viewfinder does not show 'MF' (unless I switch the lens to 'MF'). If I unmount and remount the lens, the problem goes away.

I've also noticed that the autofocus is not as smooth as my 16-50mm. With the lens cap on, the lens will focus across the full range; the 15-60 does this very smooth, but the 50-135 is very slightly 'lumpy'. I doubt if I would have noticed this if I was not looking for problems.

I've checked the lens contacts and the look clean and functional, though I am not sure which contacts are used for what purpose.

To make matters a little more complex, I purchased a 50-135mm f2.8 from Amazon 'warehouse deals' four weeks ago. The lens is categorized as 'used', but is in the box and in its original bag, so it appears completely new, with the only issue a tear in the box. I get to return the Lens for up to 30 days, which is nearly up. I got a great deal on the lens (570 USD), so I am reluctant to return it if I don't have to. The lens did not include the warranty card, but none of my other Pentax lenses did either.

- Any suggestions?
- Is this type of problem normal with autofocus lenses, or rare?
- Is it likely to be a significant fault?
- Does anyone have a 16-50 & 50-135 that they could check to see if the motor should be the same smoothness?


I would appreciate any help!

Thanks,

Jonathan
Sometimes it seems to get confused if you mount the lens with the camera switched on. The 50-135 does seem rather prone to early failures and the first signs are normally intermittant inability to focus followed by the AF failing altogether after a time.

Mine is fine, and smooth, but slower than the 16-50. If yours is rough or noisy I would send it back (just like the last person did!!!).
01-23-2009, 11:10 AM   #4
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The 50-135 makes slightly more noise than the 16-50, but I would not have noticed if I were not looking for it. So far, reseating the lens has resolved the problem.

01-23-2009, 11:57 AM   #5
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QuoteOriginally posted by jfsavage Quote
The 50-135 makes slightly more noise than the 16-50, but I would not have noticed if I were not looking for it. So far, reseating the lens has resolved the problem.
Sometimes when seating a lens I realise I havent twisted the lens to the lock point.

If you have a 12 month warranty you are probably OK, dont worry. The 16-50 has a smaller focus group so it just moves faster and probably is very slightly quieter.

But if the lens starts squeaking its about to go AWOL.
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