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09-05-2011, 02:52 PM   #1
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Apperture Priority Setting on Sigma 70-300mm Zoom

Hi All,

I'm still exploring my K-x's capabilities being quite new to DSLR photography. I decided to have an experiment with aperture priority with my cheapish Sigma 70-300mm zoom lens. The lens support aperture down to f4-f5.6 according to the documentation and indeed on the auto setting it does exactly that. However, when I set the camera to Av aperture priority, the camera seems to have a mind of its own when I try to bring the f number down to anything like this, sometimes jumping to a larger f number by itself when I turn the setting wheel.

I can set it manually on the lens but should I have to do this?

Any ideas?

Sorry if it's a dumb question.

09-05-2011, 04:56 PM   #2
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The minimum aperture is a variable that depends on the focal length you've picked on that lens. So at 70mm you'll get f4 and at 300 you'll get f5.6. I wonder if that's what you're noticing? I happen to have the same lens and I don't notice the aperture changing on me in Av unless I change focal length.
09-05-2011, 05:04 PM   #3
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Two things come to mind. First, make sure all the lens contacts are clean. Second, make sure you aren't spinning the wheel to quickly. I've seen that "confuse" my K10D.
09-05-2011, 09:11 PM   #4
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Thanks for the early replies folks. It kind of confirms that I'm not completely mad. On most occaisions I can't get down to f5.6 on Av never mind f4 but the strange thing is that with the camera on full auto it does. I'll give the contacts a clean tomorrow and have another go.



12-11-2011, 05:08 AM   #5
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Just a belated update to this thread. The K-x actually turned out to be faulty and Argos gave me the option of a new replacement which is now the K-r if I paid the 30 difference, which I did.

Thanks for the suggestions though.

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