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10-15-2010, 04:06 PM   #1
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Sigma 1.4x converter with K10D - Wrong Info?

Hi there

This is my first real post on here - I have tried to search the forums for an answer to this and can't find one.

I just bought a sigma 100 - 300 f4 (non-DG) from the marketplace, and have paired it up with a new 1.4x sigma converter (DG).

I'm quite bemused. When both are mounted my K10D does not register the focal length or aperture change from the converter. It thinks I'm at 300mm f4, when it should be 420 f5.6. Surely this is going to cause a problem for my SR?? I'm not sure if I've made some mistake or have a dud copy of the TC.

Any help?

Thanks in advance

Dan

10-15-2010, 04:18 PM   #2
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QuoteOriginally posted by ddekadt Quote
When both are mounted my K10D does not register the focal length or aperture change from the converter.
None of the TCs in existence modifies the data from the lens (changes in focal length and in aperture). They just pass the data as is from the lens to the camera body.

The only exception is the Pentax 1.7X AFA, which modifies the aperture data and blocks the focal length data.
10-15-2010, 04:20 PM   #3
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Thanks for the reply. So what does that mean re: SR? Do I need to turn it off when I use the 1.4? I suppose it's not a problem as I should be shooting from a tripod anyway.

Thanks!
10-15-2010, 04:22 PM   #4
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I leave SR on when using the TC with the 100-300mm f4 or 70-200mm f2.8.

I just presume having some SR is better than none as I don't us a tripod.

10-15-2010, 04:24 PM   #5
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Thanks for the info
10-15-2010, 04:25 PM   #6
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Re: SR, there's not much you can do. You can either turn it off or leave it on (with incorrect FL).

If you use a tripod, you should turn it off (or use the 2sec delay timer, which turns off SR).

For hand-holding situations, you should leave SR on. It will not as effective as with correct FL data, but IMHO, it doesn't hurt.
10-15-2010, 04:49 PM   #7
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You may want to check the exposure with and with out the TC. There will be some error due to an interesting non linearity of the metering and focusing screen. Since the lens's native aperture is F4 o would expect about .3 to .7 ev is needed with the 1.4x
10-15-2010, 04:50 PM   #8
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Yes, I noticed in the field that shots with the 1.4 seemed consistently underexposed. I will do some more comparative shots when the weather here clears up.

10-15-2010, 05:21 PM   #9
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Forget comparative shots. Use a plain surface evenly illuminated

Test in Av mode and dial in each aperture using the body to control aperture

Measure grey scale value with your photo editor

My sigma 70-200 f2.8 had a constant shift of 30 grey scale which is about .7 stops
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