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08-16-2009, 12:52 PM   #1
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50-135mm troubles or is it me?

Hello,

I recently acquired a 50-135mm f2.8 and was hoping anyone else who owns this lens could shed some light on a few questions.

As a side note, I also own the 16-50mm f2.8 so I have been comparing sharpness and autofocus ability to this lens (which may or may not be a terrible idea).

Anyway, I've noticed that the focus on my lens can be very finicky. For example, I can point the lens at a car 20 feet away, hit the autofocus button and the lens focuses to that point and stops. However, if I zoom into 135mm and try to shoot something, say, 5 feet away the autofocus reaches the point at which the object is in focus, then begins to "second guess itself" by moving in and out of focus several times.

Is this lens more finicky at close focus distances?

Also, if anyone has any experience using the 200mm f2.8, as well as this lens, I am wondering which one you prefer. I am still able to return this lens and purchase the 200mm, but I'm on the fence about it all together.

Quick responses appreciated.

08-16-2009, 01:29 PM   #2
DAZ
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Are you in AFC or AFS? In AFC the camera will keep trying to and will change focus with even a small movement of the camera. 5 feet is near the close focus limit of the lens but it should still not have a problem. The 50-135 needs more turns at the short end (this also make it slower) so it is a little less sensitive to focusing but at 135mm f/2.8 at a short focus the DOF can get small. If the light is low with a low contrast target and/or you are using AFC this could be what you are seeing.

DAZ
08-16-2009, 10:31 PM   #3
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QuoteOriginally posted by DAZ Quote
Are you in AFC or AFS? In AFC the camera will keep trying to and will change focus with even a small movement of the camera. 5 feet is near the close focus limit of the lens but it should still not have a problem. The 50-135 needs more turns at the short end (this also make it slower) so it is a little less sensitive to focusing but at 135mm f/2.8 at a short focus the DOF can get small. If the light is low with a low contrast target and/or you are using AFC this could be what you are seeing.

DAZ
Yeup... something I noticed too.
Never use AF-C with static objects... EVER.

Try AF-S and tell us how it works. My 50-135mm is occasionally finicky but that is in low light situations... and it still is ocasional even then.
08-17-2009, 08:27 AM   #4
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Changing this helped and was definitely a user error (ie, just purchased a k20 and that was the only setting I had forgotten!)

Thanks for the reminder and your help. Now my only problem is the focal length is too small!

Thanks

08-17-2009, 10:30 PM   #5
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If focal length is to small, might i suggest the Sigma 100-300mm i have for sale.

$950

https://www.pentaxforums.com/forums/photographers-marketplace/70022-sale-trad...m-f4-more.html
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