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04-21-2010, 09:29 AM   #1
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Could anyone tell me if k7 or kx can af with slow glass such as a 4-5.6 behind a teleconverter?

thanks..

04-21-2010, 10:19 AM   #2
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QuoteOriginally posted by andie80 Quote
Could anyone tell me if k7 or kx can af with slow glass such as a 4-5.6 behind a teleconverter?

thanks..
I've tried my 1.4x (Tamron Pz-AF) with several f/4 lenses (Sigma 100-300/4, DA*60-250/4, DA*300/4, DA55-300/4-5.8) and the AF systems of the Kx and K7 will find and lock focus most of the time, although it's not as fast or reliable as without the TC. It also works best if you are already close to being in focus before using the AF.
04-21-2010, 10:26 AM   #3
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I have 1,4 x and 2 x TC`s for my Sigma 500/4,5.
With the 1,4 x TC AF becomes sluggish, but works most of the time. With the 2 x TC it is a manual focus lens.
04-21-2010, 10:57 AM   #4
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They can indeed focus, although not as well or as fast. More to the point, IQ from these consumer zooms when used with TC is usually worse than simply shooting without the TC and then cropping - plus you don't pay a penalty in maximum aperture or in focus speed. It's really only the faster / higher end lenses that stand a shot of being helped by a TC.

04-21-2010, 11:44 AM   #5
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Like others have mentioned it should focus but it will be slow and in bad light it could hunt quite a bit. It is one of those things that you have to try and see if you can deal with it.



John
04-21-2010, 11:50 AM   #6
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QuoteOriginally posted by andie80 Quote
Could anyone tell me if k7 or kx can af with slow glass such as a 4-5.6 behind a teleconverter?

thanks..
I have been rather extensively testing the Kenko 1.5x and 2x TC's with my K-x and DA L 55-300mm lens. AF is usable - albeit slow - with the 1.5x, provided there is decent light (sunny or bright clouds) and plenty of contrast. AF is nearly unusable with the 2x TC, except in very good light.

In case you didn't know, the DA L 55-300 is f/4 - f/5.8.

IQ with often noticeably better than a 100% "crop" from the 55-300.

I'll be doing a bit of a comprehensive write-up on using the TC's at some point this weeked.

Samples:

https://www.pentaxforums.com/forums/post-your-photos/97911-nature-early-sampl...converter.html

https://www.pentaxforums.com/forums/post-your-photos/98357-nature-4-more-bird...o-1-5x-tc.html

https://www.pentaxforums.com/forums/post-your-photos/98654-nature-early-shots...at-flower.html
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