Sigma APO 400mm Tele Macro+Sigma 1.4X

Ducatigaz · 08-09-2010, 05:18 AM

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

Adam · 08-09-2010, 05:23 AM

Yes, it will. See the Sigma 1.4x teleconverter review.

snostorm · 08-09-2010, 08:49 AM

Originally posted by Adam

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

Talisker · 08-09-2010, 02:22 PM

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...

08-09-2010, 05:18 AM	#1
Ducatigaz Pentaxian Join Date: Feb 2010 Location: Blunsdon,Wiltshire, UK Posts: 1,254	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
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 49,785	Yes, it will. See the Sigma 1.4x teleconverter review. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

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08-09-2010, 08:49 AM	#3
snostorm Pentaxian Join Date: Oct 2006 Location: Chicago suburb, IL, USA Posts: 1,535	Originally posted by Adam 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
Talisker Senior Member Join Date: Nov 2007 Location: Isle of Skye, Scotland Photos: Gallery Posts: 262	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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