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Old Mar 4, 2011, 10:10 AM   #1
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Join Date: Jul 2010
Location: Indianapolis, IN
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Default A100 Kit lens auto focus question (18-70mm)

I while back, my 18-70mm lens for my A100 stopped auto focusing. It still works as a manual focus though. I recently (yesterday) upgraded to a new A55. I was curious so I popped the old 18-70 lens on the new camera and low-and-behold, the auto focus worked. However, when turning the camera on (and off), there was a horrible gear grinding sound. Needless to say, I won't be doing that again (I am selling it anyway).

I put the lens back on the A100 and the gear grinding sound, which hadn't happened on the A100 before, happened. It still would not auto focus.

Any ideas why it would auto focus on one camera and not the other? I have three other lenses that all auto focus on the A100 with no issues and no grinding gear sounds.
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Old Mar 4, 2011, 1:33 PM   #2
Join Date: Jun 2003
Location: Savannah, GA (USA)
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Check for mechanical problems (loose screws in camera lens mount, lens, etc.).

If you have loose lens mount screws on the lens or camera (so that the camera screw drive and slot for it to mesh with in the lens are not engaging properly), that can cause problems with the screw drive mechanism for focusing and may be what's causing the grinding you're hearing.

If the problem occurs on more than one camera, it's probably a lens issue. If the problem isn't obvious (tighten the mount screws on the lens and/or camera and all works fine), then I'd just get another lens. Just look at the camera mount with the lens removed and you'll see screws in the round mount you can tighten. Ditto if you're looking at the lens with it removed. Sometimes those screws come loose and prevent a solid connection between the camera and lens.

It the problem is internal to the lens (internal gears, etc.), versus a mechanical problem with how the camera's focus screw drive and lens mesh together, then I'd just get another lens (as the 18-70mm kit lens isn't worth a lot anyway, and a replacement shouldn't cost you much).
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Old Mar 4, 2011, 3:13 PM   #3
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Default Probably the lens but I was already selling it.

The grinding noise happens on both cameras whenever I attach the lens. I don't hear that noise when I attach any of my other three lenses. That and the fact that it will auto focus on one body but not the other lead me to believe it is a mechanical issue with the lens itself.

I am not looking for a replacement since I bought a Minolta 28-105 back in July (in large part based feedback from yourself and TCav).

I just bought the A55 (Body Only) with an extra Sony 55-200 because Crutchfield was running a $100 instant savings on specific sony lenses with a camera purchase. I couldn't pass up a telephoto for the price of the 18-55 kit lens.
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