Using a teleconverter


ggsupersport

Link Posted 04/07/2012 - 18:00
I am using a Pentax K10 with a Tamron 18-200 lens, and it works fine on automatic settings
I have a Bower MC 2X Pz/AF teleconverter, but when I added this, it did not seem to want to "auto" focus. I manually focused and got a great shot. Shouldn't it auto focus? (I was shooting through a window)

bforbes

Link Posted 04/07/2012 - 18:07
Could be the lack of light being let past the converter, (You lose 2 stops on your exposure don't forget.) that makes it difficult for the AF system. I've tried a few converters with different lenses and if happens often
Barrie
Too Old To Die Young

http://www.pentaxphotogallery.com/artists/barrieforbes
https://www.flickr.com/photos/189482630@N03/

ggsupersport

Link Posted 04/07/2012 - 18:11
Thanks Barrie, I will play with it in brighter light.....

Mike-P

Link Posted 04/07/2012 - 18:18
What's the 18-200mm at the long end .. f6.3?. If so then with a 2x converter you will be shooting wide open at approx f13.

No, I doubt very much it will AF and if it did it would be very slow and unreliable.
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ggsupersport

Link Posted 04/07/2012 - 18:34
Mike-P,
Yes it is 6.3. I understand what you are saying, but don't know why at f13 it would not "auto" focus. I am way over my head in the equipment I have...I try to learn, but forget so rapidly.

Mike-P

Link Posted 04/07/2012 - 18:45
As an example Canon cameras are not able to AF with a teleconverter on any lens that takes it over f5.6 (or f8 on their pro range bodies).Therefore I can use my 1.4x TC on a Canon 70-200mm f4 (for instance) as this will take it to f5.6 but I cannot use the same lens with a 2x converter as it will take it to f8.

The reason for this is that Canon don't want people taking iffy shots with their lenses/converters and then blaming the equipment when it is quite obvious that you are not going to get a sharp shot at f13 400mm without ideal conditions. By making it manual focus only they are saying yes you can do it but use your own skills to get there and if it doesn't work then don't blame us.

Now I don't know for certain if this is the case with Pentax but I would guess it is.
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Last Edited by Mike-P on 04/07/2012 - 18:46

ggsupersport

Link Posted 04/07/2012 - 18:51
Thank you Mike, that sounds reasonable.

bforbes

Link Posted 04/07/2012 - 18:57
I also think it may have something to do with the construction of a zoom lens. I have a Tamron 70-200 which is supposed to be F2.8 at both ends but I can not get it to AF with a converter. (Kenko 1.5x or Pentax 1.7AF)
Barrie
Too Old To Die Young

http://www.pentaxphotogallery.com/artists/barrieforbes
https://www.flickr.com/photos/189482630@N03/

Mike-P

Link Posted 04/07/2012 - 19:06
bforbes wrote:
I also think it may have something to do with the construction of a zoom lens. I have a Tamron 70-200 which is supposed to be F2.8 at both ends but I can not get it to AF with a converter. (Kenko 1.5x or Pentax 1.7AF)

That's very strange, the 1.7x should AF with almost any fast(ish) lens because its the converter itself doing all the work.

My Sigma 70-200mm f2.8 has worked with every TC I have tried.
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johnriley

Link Posted 04/07/2012 - 23:34
I think the Pentax converter needs f2.8 or faster lenses to work properly.
Best regards, John

seaside

Link Posted 05/07/2012 - 08:54
bforbes wrote:
I also think it may have something to do with the construction of a zoom lens. I have a Tamron 70-200 which is supposed to be F2.8 at both ends but I can not get it to AF with a converter. (Kenko 1.5x or Pentax 1.7AF)

That's a bit odd. Have you ever tried it with a Tamron 1.4X Pz-AF MC4?

paulgee20

Link Posted 05/07/2012 - 09:18
I have a Kenko x2 and it will only auto focus with Pentax lenses. Im not sure they are compatible with others, maybe be wrong though. It certainly doesnt with my Siggy lenses.

Paul
K5's (2)both gripped, K10d gripped, Pentax 28-90 f3.5, Sigma 18-250mm, Sigma 150-500mm. Sigma 105mm f/2.8 EX DG Macro, Sigma 10-20 f.4-5.6.EX DC, Hoya 135 f2.8, Take on 28mm f2.8 Pentax AF360 flash, 2 fill in slaves. 30 metre remote release, Rt angle viewfinder, Giotto NOT 3261B Tripod with Manfrotto 808Rd4 ball head, Manfroto 4861RC2 monopoly, shoulder stock, various filters etc, Panasonic SET HBS HD Video cam, Tamrac Explorer 8x backpack and a sore back.....
-------------------------------------------------------
Photography is an index for measuring futility and pride.......

Paul

:wink
http://s743.photobucket.com/home/pg20_photos/index http://www.flickr.com/photos/pg20

bforbes

Link Posted 05/07/2012 - 09:20
No, I have not tried the Tamron 1.4.

Since a trip out with Blythman I've been using the green button to operate the AF. So yesterday when I tried 70-200 f2.8 with the Kenco 1.5 and with a Teleplus 2x MC7 I was surprised that they worked after a fashion. I can not think of any logic as to why the green button would make a difference?

Also the AF was no where near as fast as the Tamron 300 F2.8 with Pentax 1.7AF
Barrie
Too Old To Die Young

http://www.pentaxphotogallery.com/artists/barrieforbes
https://www.flickr.com/photos/189482630@N03/

seaside

Link Posted 05/07/2012 - 10:24
I ask because I know the 70-200 works with the Tamron 1.4.

Unfortunately I haven't tried it with the other converters you mention.
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