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11-05-2010, 06:13 PM   #1
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zoom on an autofocus lens

the last couple of lenses that i've purchased for my sf1 i noticed something i didn't expect. the first was a pentax 35-80 f smc 4.0-5.6. the guy said it was untried and sure enough it works sporadically .the next lens is a 28-80 3.5-4.5 pentax takumar
finally i had winner. but on both lenses the zoom rings turned extremely slow. i feel as though something might break. am i doing something wrong?

11-05-2010, 07:05 PM   #2
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Do you mean they are hard to turn? Make sure you aren't turning the focus ring.
11-05-2010, 07:33 PM   #3
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Wait--your title says "Autofocus Lens" These are actually manual focus, right? Also, checking the Lens reviews, I get the impression that the 28-80mm F3.5-4.5 is not a highly regarded lens.
11-06-2010, 06:46 AM   #4
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to my knowledge these things don't auto zoom.i think that i'm turning the zoom ring. they both feel really heavy.unusually so. they are definitely the zoom ring. they are definitely auto focus.

11-06-2010, 07:56 AM   #5
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QuoteOriginally posted by newpentaxman Quote
to my knowledge these things don't auto zoom.i think that i'm turning the zoom ring. they both feel really heavy.unusually so. they are definitely the zoom ring. they are definitely auto focus.
Hrm, hard to tell. If they were power zooms, you'd likely see a switch on the side, as I recall. A tight zoom ring is a pretty rare complaint, (They're much more likely to get loose, if anything) never mind to have occur twice. Assuming there's no confusion on your part, I wonder if they might have been subjected to some really bad storage conditions together.

Is it like grindey-feeling or smooth-but-stiff like there's gunk in there, or are they scrapey-tight, or something else perhaps? Maybe some lubrication got gummy in there or something.
11-06-2010, 11:24 AM   #6
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The SF1 does not support power-zoom lenses. In film cameras, I believe that only the PZ series did so. Some Pentax dslrs partially support it. My K10D has the contacts for the SDM lenses, which also provide power to the zoom. The basic power zooming works on my K10D, but some of the more advanced features do not.

The one power-zoom lens that I have switches from power to manual zoom by sliding the zoom ring forward or backward, along the lens' axis. I don't have it in front of me, so I don't remember which way is which.

Try pushing the ring forward or pulling it back, toward the camera.
11-06-2010, 11:50 AM   #7
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Neither lens described is a power zoom. The zoom ring should turn smoothly with some resistance, but not much. It sounds as though they are already broken. "Untried" is eBay-speak for a lens that is faulty in some way that is not visible in a photograph.
11-06-2010, 10:13 PM   #8
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the 28-70 feels the way ratmagic lady describes it.it auto focus's jut fine. the 35-80 works when it wants to and is also very heavy in the zoom. it's just my luck to get two in a row i guess. who conditions these?

11-10-2010, 07:24 PM   #9
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I'm sure Eric at Home can fix these lenses -- but it's probably not cost-effective. Probably cheaper to buy another that is asserted to be in good repair.
11-16-2010, 10:14 PM   #10
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QuoteOriginally posted by dadipentak Quote
Wait--your title says "Autofocus Lens" These are actually manual focus, right? Also, checking the Lens reviews, I get the impression that the 28-80mm F3.5-4.5 is not a highly regarded lens.
It was cheap and was OK for snapshots, but not much more. We still have one with packing tape holding the power zoom switches on the lens. It's nothing at all to compare with the 24-90, which is a very nice lens.
11-17-2010, 01:57 AM   #11
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QuoteOriginally posted by newpentaxman Quote
the 28-70 feels the way ratmagic lady describes it.it auto focus's jut fine. the 35-80 works when it wants to and is also very heavy in the zoom. it's just my luck to get two in a row i guess. who conditions these?
The Takumar is a manual lens, while the FA-J 35-80 is an AF lens but it does not have a power zoom or the switch.
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