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05-13-2015, 06:18 PM   #1
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Can't adjust aperture ring

I recently purchased a second hand Sigma 100-200m f4.5 lens, but when I attach it to my K3, no matter how I adjust the aperture ring, the aperture doesn't change on the lens. For some reason, this lens also has an aperture tab, though there are no pins. Consequently, the aperture is wide open no matter what I do. If anyone knows about this and has a workaround, I would like to know.

Thanks.

05-13-2015, 06:30 PM   #2
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QuoteOriginally posted by halfaura Quote
I recently purchased a second hand Sigma 100-200m f4.5 lens, but when I attach it to my K3, no matter how I adjust the aperture ring, the aperture doesn't change on the lens. For some reason, this lens also has an aperture tab, though there are no pins. Consequently, the aperture is wide open no matter what I do. If anyone knows about this and has a workaround, I would like to know.

Thanks.
The aperture will stop down only when you go to take a picture, otherwise it will stay wide-open.

If the aperture ring doesn't have an A setting, here's what you need to do to expose properly:
https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...k-x-k-7-a.html

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05-13-2015, 06:53 PM   #3
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If you have the DOF preview set to optical when you operate the DOF preview lever (on-off switch) it should stop down.
05-13-2015, 08:06 PM   #4
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That's a pretty early one, probably does not have an A setting (would be next the smallest aperture, so you'd see an A on the apeture ring next to f/22 or f/16 -- whatever it is on that lens). If that's the case, you must use (M)anual mode on the body or it will never ever stop down -- see Adam's link.

05-13-2015, 09:35 PM   #5
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Ah, seems to have worked. Thanks.
05-15-2015, 01:32 AM   #6
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If you ever come across a lens where you follow all these steps and it still doesn't stop down.

Check if the base of the lens mount is covered by a coat of paint.

Chinon are a great example of this and you need to scrape it off where the pins would normally be. Otherwise the camera cannot detect it.
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