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07-02-2011, 09:36 AM   #1
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Tamron 18-200 focus resistance

I bought my wife a Tamron 18-200 recently for casual use. We're not disappointed with it optically - we didn't expect it would measure up to our primes - but sometimes, her K100D really struggles (mechanically) to focus it. It often just gives up and won't lock focus in situations where you wouldn't expect the AF sensors themselves to be struggling. It works noticeably better on my K200D. I guess there is probably a difference in the strength of the focus motors. On her camera, it's a single spin then fail; on mine, it's spin, reverse, spin, reverse, spin, reverse, succeed. Yet none of our other AF lenses have difficulties on her K100D.

I'm wondering if our 18-200 is unusual / defective in providing more resistance to the AF system than it should, or if that's a trait of this lens? Even the MF ring is very stiff. I hadn't seen these *specifically* mentioned as issues with this lens.

If it's just how the lens is, I'm also wondering if other superzooms would be noticeably better in that respect? Yes, I know they are optically better, but that's not worth anything if her camera will struggle to focus them too. And then we get to a price range where replacing the camera starts to sound equally attractive.

07-02-2011, 05:35 PM   #2
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Marc,

I recently sold a Tamron 18-200 to my brother. I had been using it on my K200D with no focusing problems, and now he is using it on his K100D and has not mentioned any problems. Maybe you have a stiff one.

John
07-03-2011, 09:32 AM   #3
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Marc,
When does it have trouble focusing? In a dark room, or when zoomed in to 200mm?
Does it perform any better on the K100D in a brighter setting, or when zoomed out to 18mm?
Glen
07-03-2011, 04:16 PM   #4
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I haven't had enough opportunity to test to narrow things down further, and she's out of town right now so I won't be able to for a few days. But the time I saw it with my oen eyes, it was outdoors, near sunset but still lots of light, and at 18mm.

07-03-2011, 04:48 PM   #5
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QuoteOriginally posted by Marc Sabatella Quote
I haven't had enough opportunity to test to narrow things down further, and she's out of town right now so I won't be able to for a few days. But the time I saw it with my oen eyes, it was outdoors, near sunset but still lots of light, and at 18mm.
Stopped down @18mm I'd have a impossible time finding the focal plane too, which probably extends from a few feet to infinity.
07-04-2011, 10:42 PM   #6
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Not sure what stopping down would have to do with anything - focus is done wide open. And like I said, it worked fine on my K200D. The K100D simply turned the focus ring once then stopped, which is not the normal way a lens fails to focus lock.
07-05-2011, 11:23 AM   #7
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Yes focus is wide open, but what was the subject distance in each case? More than, say, 15 feet at f/3.5?
07-06-2011, 07:42 AM   #8
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Probably just over 15 feet. But again, I'm not talking about ordinary failure to lock, which wouod usually involve several turns of the focuw ring. I'm talking about an unusual mechanical situation where the lens just stops after one turn.

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