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07-23-2012, 07:56 AM   #1
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Need help Sigma lens not working

Hi all, I just joined the forum hoping i could get some help.

I recently purchased a Sigma 20-40mm F2.8 DG lens off ebay. I have a Pentax K-x, the problem i am having is that with that lens mounted with the aperature control ring in the A position the aperature read out on the lcd blinks between F-- and F1.2 (sometimes F1.4). Also the autofocus is not working. I dont think its a camera issue because i have another Sigma lens (28-200mm F3.5-5.6) which works perfect.

I have tried cleaning the contacts with alcohol and i have used the eraser, i have tried tightening the lens and body mounts and now i m out of ideas. I know this type of problem has been asked before but i cant find any definitive answers. Any help would be appreciated thanks.

07-23-2012, 08:20 AM   #2
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Not sure this will help but might give some additional info. Check that "use aperture ring" is turned on in the menu. Now see what happens if you turn the aperture ring away from the A setting. You should see F-- not flashing. Turn back to 'A' you should see the aperture as set on the camera.
07-23-2012, 08:26 AM   #3
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Hey jatrax, thanks for the reply i have that already enabled in the menu since some of my other lens require that setting. It doesnt explain the blinking to F1.2 which is weird because the max aperature for the lens is F2.8. Also forgot to mention the lens works normally in the full manual mode.
07-23-2012, 09:26 AM   #4
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QuoteOriginally posted by Mod 16 Quote
It doesnt explain the blinking to F1.2 which is weird because the max aperature for the lens is F2.8.
Nope, did not expect it to, but when troubleshooting I have found that sometimes when you are stuck it helps to just gather data, even unrelated stuff can suddenly result in an "ah ha" moment. So with the lens in the "not A" position does anything change? Or do you get the same error state?

Another thing to check is to see if all of the pins are correctly aligned, look at the lens mount and see if the little gold contacts all are in place and centered as they should be, compare to another lens. If one of the pins is miss-aligned or shorted improperly that will give you bad aperture readings.

Next thing to check, if you have access to it, would be another camera. If you get the same result on two different cameras then that is pretty definitive that the lens is faulty. Normally the solution would be cleaning the contacts, which you have already done. So I would then go back to the seller with a complaint, assuming you just got this it should not be hard to send it back as defective.

07-23-2012, 10:27 AM   #5
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i have some sigma lens and periodically i will get the f---.... i have a little play in the lens and when i tweak it slightly on the camera it will start working...i have seen this with both the teleconverter and the 70-200...good luck
08-19-2012, 09:02 AM   #6
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Mod 6 - Did you ever resolve this issue? I am having the same problem with my K5 and two lenses (one is a Ricoh with a P mode and the other is a Pentax FA 80-320mm lens.)

Wondering if my K5 is the issue....

I have tried both of the aperature ring modes.

When I turn off Permit Aperature Ring = Prohibited, I get the F-- blinking. Have tried "wiggling" lens with no luck...

Open to other suggestions.


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