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andie80 · 04-21-2010, 09:29 AM

Could anyone tell me if k7 or kx can af with slow glass such as a 4-5.6 behind a teleconverter?

thanks..

dgaies · 04-21-2010, 10:19 AM

Originally posted by andie80

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.

PePe · 04-21-2010, 10:26 AM

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.

Marc Sabatella · 04-21-2010, 10:57 AM

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.

palmor · 04-21-2010, 11:44 AM

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

flippedgazelle · 04-21-2010, 11:50 AM

Originally posted by andie80

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

04-21-2010, 09:29 AM	#1
andie80 New Member Join Date: Mar 2009 Location: Sweden Posts: 3	new pentax dslr Could anyone tell me if k7 or kx can af with slow glass such as a 4-5.6 behind a teleconverter? thanks..

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04-21-2010, 10:19 AM	#2
dgaies Veteran Member Join Date: Oct 2009 Location: Maryland / Washington DC Posts: 3,917	Originally posted by andie80 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, DA60-250/4, DA300/4, 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
PePe Pentaxian Join Date: Nov 2007 Location: Helsinki, Finland Photos: Gallery \| Albums Posts: 597	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
Marc Sabatella Veteran Member Join Date: Sep 2006 Location: Denver, CO Photos: Gallery Posts: 10,685	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
palmor Veteran Member Join Date: Dec 2006 Location: North of Boston, MA Posts: 798	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
flippedgazelle Veteran Member Join Date: Apr 2009 Location: NJ, USA Photos: Albums Posts: 1,270	Originally posted by andie80 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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