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08-09-2010, 05:18 AM   #1
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Sigma APO 400mm Tele Macro+Sigma 1.4X

Does anyone know if the auto focus will still work on a K20D with a Sigma 400mm APO Tele Macro + Sigma 1.4x Convertor fitted?
Cheers Gary

08-09-2010, 05:23 AM   #2
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Yes, it will. See the Sigma 1.4x teleconverter review.

Adam
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08-09-2010, 08:49 AM   #3
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QuoteOriginally posted by Adam Quote
Yes, it will. See the Sigma 1.4x teleconverter review.
Now this is just weird. I read the posts in the link given and the second one says that AF will not work with this combo -- that the TC will mount on this lens, but it will be MF only. The OP distinctly asked if AF will still work. . .

My first guess (I don't own the Sigma 400/5.6 APO Macro) would be that it might gain an AF lock in the brightest sunlight conditions with a good contrast border, but it would struggle with anything less. Add 1 stop to the f5.6 max aperture and you get an effective max aperture of f8.

I use TCs more than not, and my experience says that an f8 max effective Av combo has little chance of anything close to acceptable AF performance.

Scott
08-09-2010, 02:22 PM   #4
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For what its worth, my Tamron 1.4x and Tokina 400mm f5.6 ATX worked suprisingly well together and would AF in quite gloomy conditions, so its probably hit and miss. The Tokina is more or less retired since I bought the Sigma 100-300mm/1.4x - much sharper even when enlarged to give the same framing as the 400mm...

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