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02-03-2014, 02:59 PM   #1
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Sigma 150-500mm lens AF won't work

I purchased a Sigma 150-500mm lens new several years ago to use with, at that time, my Pentax K5 for wildlife photography. I have been thinking of selling it because the AF system has not worked with any of my Pentax dslr camera bodies from the day it arrived. I have tried it on my 200D, my K7, my K5 and now on my new K3. I can only take photos using the manual focus system. When I try to use the AF, the lens AF system just shutters like it cannot get the elements inside to align properly. In reading the lens reviews, it appears I am unique at having this problem. Is there a way to correct it? Any constructive help would be most appreciated.

02-03-2014, 03:25 PM   #2
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Does that lens have the push/pull AF/MF clutch? If so you might check to see if it is in the correct position or maybe stuck partway. Just a thought.
02-03-2014, 03:27 PM   #3
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I assume you have pulled the focus ring in and out several times from MF to Auto focus using a bit of force.
02-03-2014, 03:28 PM   #4
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It should have been returned immediately. It's defective. I returned a Sigma 120-400 for the same reason.

02-03-2014, 03:43 PM   #5
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QuoteOriginally posted by jatrax Quote
Does that lens have the push/pull AF/MF clutch? If so you might check to see if it is in the correct position or maybe stuck partway. Just a thought.
Thank you for your quick response. It has the AF/MF slide switch. I am not sure what is meant by clutch.
02-03-2014, 03:46 PM   #6
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QuoteOriginally posted by DC Cebula Quote
I am not sure what is meant by clutch.
Some of those 'bigma' style lenses have a large collar ring that slides forward or back to allow MF or AF. It is a complete ring, not a switch. If you don't have that then I suspect you have a newer model, so my thought probably does not apply.
02-03-2014, 03:50 PM   #7
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QuoteOriginally posted by jatrax Quote
Some of those 'bigma' style lenses have a large collar ring that slides forward or back to allow MF or AF. It is a complete ring, not a switch. If you don't have that then I suspect you have a newer model, so my thought probably does not apply.
Thank you. I thought I should have returned it right away but thought the error was in something I was doing.
02-03-2014, 03:51 PM   #8
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Make sure the AF switch on the lens is moved all the way. Switch to MF then back to AF.

A test to try: Manually focus close up then try to AF on something near infinity. Does the focus point change at all? Then manually focus to infinity and try to AF on something close up. Knowing the results of those tests might reveal something to help diagnose the problem.

Try pointing the lens upwards or downwards. Does behavior change? If the focusing motor is dying then gravity might help move the lens.

Regardless, it sounds like some sort of repair is needed.

02-03-2014, 03:52 PM   #9
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Try pulling the first collar in and out and see if it moves or look at the collar and see if you can see AF or MF printed on the the main barrel next to the collar. I am probably a bit confusing as my 50-500 is out on loan and i can't look at it,
02-03-2014, 04:07 PM   #10
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I thought sigma had a 10 yr warranty. Send it in
02-03-2014, 05:17 PM   #11
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Put the camera on AF-C and move the focusing ring multiple times, also past each end of the scale, wile using the the AF. That was how I brought my 70-200 to life when stuttering before I got it serviced. It was "dirt" in the motor possibly due to a lack use by previous owners that was the culprit.
02-04-2014, 07:50 AM   #12
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Thank you

Thanks to all of you for your suggestions.
02-04-2014, 10:01 AM   #13
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The repair of my 70-200 cost me 130€ so it's probably worth it to get it repaired even if you're gonna sell it.
05-06-2014, 03:04 PM   #14
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QuoteOriginally posted by normhead Quote
It should have been returned immediately. It's defective. I returned a Sigma 120-400 for the same reason.
Normhead, did you keep your serial number by any chance? I just got one and the darn thing won't focus neither in AF or MF, nothing moves when I turn the focus ring and when in AF it makes the normal SDM noise but nothing moves. As I was opening the box I had the feeling that the lens wasn't new. I'm just curious to see if they just put yours back in the pile...
05-06-2014, 04:06 PM   #15
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People are confusing the Tamron clutch (push-pull barrel). Sigma has a switch only. Sigma has a 3 (or 4?) year total warranty IF it is registered.

Your choicies are use it MF, send it in for service,. or sell it.
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