DA 70mm F/2.4 Ltd.

**fredok1** · 06-14-2010, 08:31 AM

Why would a Pentax DA 70mm f/2.4 Ltd. lens not autofocus with a Kenko Pz-AF 2X teleconverter while a DA 21mm f/3.2 lens will autofocus with the same TC?

Adam · 06-14-2010, 08:34 AM

It should work. Why wouldn't it? Both lenses use the same screwdrive-based AF system.

**fredok1** · 06-14-2010, 09:03 AM

Originally posted by Adam

It should work. Why wouldn't it? Both lenses use the same screwdrive-based AF system.

In theory it should work. I based my purchase of the DA 70mm on my use of the TC with my DA 21mm. But for some reason the Kenko doesn't work with the DA 70mm in the same light and same camera body (K10D). I would have bought the FA 77mm if I had known the issue beforehand.

Adam · 06-14-2010, 09:05 AM

That's very strange. I don't see why you would ever want to use a TC with a 21mm lens (except for testing, of course), but I can see it coming in handy for the 21mm. Without the TC, does the AF work fine on your 21mm?

Adam
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**fredok1** · 06-14-2010, 09:30 AM

Originally posted by Adam

That's very strange. I don't see why you would ever want to use a TC with a 21mm lens (except for testing, of course), but I can see it coming in handy for the 21mm. Without the TC, does the AF work fine on your 21mm?

Both the 21mm and 70mm autofocus just fine without the TC. Plus I agree that the 21mm with TC are just useful for testing. But here's something even stranger. With the TC, the 21mm autofocuses on my K10D but not on my K7 body. And I just discovered (subsequent to my post) that the 70mm with TC autofocuses on my K7 body but not on the K10D. Go figure!

Adam · 06-14-2010, 09:31 AM

Sounds like some sort of electronic inconsistency. Maybe others know more about it.

Marc Sabatella · 06-14-2010, 11:31 AM

Maybe it's just insulted? It's extremely unlikely the IQ from this combo will be what you'd get simply cropping.

06-14-2010, 08:31 AM	#1
fredok1 Site Supporter Join Date: Feb 2010 Location: Colorado Posts: 58	DA 70mm F/2.4 Ltd. Why would a Pentax DA 70mm f/2.4 Ltd. lens not autofocus with a Kenko Pz-AF 2X teleconverter while a DA 21mm f/3.2 lens will autofocus with the same TC?

06-14-2010, 08:34 AM	#2
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,597	It should work. Why wouldn't it? Both lenses use the same screwdrive-based AF system. 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 purchasing one of our Pentax eBooks. 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:

06-14-2010, 09:30 AM	#5
fredok1 Site Supporter Join Date: Feb 2010 Location: Colorado Posts: 58 Original Poster	Originally posted by Adam That's very strange. I don't see why you would ever want to use a TC with a 21mm lens (except for testing, of course), but I can see it coming in handy for the 21mm. Without the TC, does the AF work fine on your 21mm? Both the 21mm and 70mm autofocus just fine without the TC. Plus I agree that the 21mm with TC are just useful for testing. But here's something even stranger. With the TC, the 21mm autofocuses on my K10D but not on my K7 body. And I just discovered (subsequent to my post) that the 70mm with TC autofocuses on my K7 body but not on the K10D. Go figure! Last edited by fredok1; 06-14-2010 at 09:32 AM. Reason: add clarifying wording

06-14-2010, 09:31 AM	#6
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,597	Sounds like some sort of electronic inconsistency. Maybe others know more about it. 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 purchasing one of our Pentax eBooks. 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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06-14-2010, 09:03 AM	#3
fredok1 Site Supporter Join Date: Feb 2010 Location: Colorado Posts: 58 Original Poster	Originally posted by Adam It should work. Why wouldn't it? Both lenses use the same screwdrive-based AF system. In theory it should work. I based my purchase of the DA 70mm on my use of the TC with my DA 21mm. But for some reason the Kenko doesn't work with the DA 70mm in the same light and same camera body (K10D). I would have bought the FA 77mm if I had known the issue beforehand.

06-14-2010, 09:05 AM	#4
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,597	That's very strange. I don't see why you would ever want to use a TC with a 21mm lens (except for testing, of course), but I can see it coming in handy for the 21mm. Without the TC, does the AF work fine on your 21mm? 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 purchasing one of our Pentax eBooks. 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:

06-14-2010, 11:31 AM	#7
Marc Sabatella Veteran Member Join Date: Sep 2006 Location: Denver, CO Photos: Gallery Posts: 10,685	Maybe it's just insulted? It's extremely unlikely the IQ from this combo will be what you'd get simply cropping.