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08-22-2007, 01:22 AM   #1
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Compatibility - Tele Adapter 1.7x & Pentax Lenses

Hullo Everybody!
I am led to believe that the 1.7x AF tele adapter is compaitble only with K and A series lenses. Can anyone here shed light on whether it can be used with F or FA series lenses in AF mode, please? And what can or will happen if one tries to use them on F/FA lenses with AF on? Thank you.

08-22-2007, 02:23 AM   #2
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I'm not sure about the autofocus functionality, and have not tried this with my lenses, BUT, most pentax AF lenses are too slow (i.e. maximum apature too small) to use successfully with autofocus when using the adaptor.

Note the manuals all state that the adaptor is to be used with F2.8 and faster lenses, however, fortunately neither the cameras or the adaptor can read because it works up to F4.0, but not any slower.
08-22-2007, 02:57 AM   #3
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I will work with all K-mount lenses, incl the F, FA and DA.

It does need enough light to retain its AF function indeed, for lenses slower than f/2.8 it will require bright light.

Even for AF lenses the in-converter AF mechanism will be used, so the lens will have to be focused on infinity manually. On SR enabled cameras the camera will ask for the focal length as the converter doesn't pass this info to the body.

hth, Wim
08-22-2007, 03:27 AM   #4
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Thanks, Wim!
Hope all is well with you; I forgot you used to have one!! Infact, you should be the right person to ask - will it work on the 100mm f3.5 you sent me? Did you try them together? What should I do to get the lens+1.7x combination to AF if, say, the subject is 1 metre away from the lens?
The very best!

08-22-2007, 04:56 AM   #5
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The 1.7x AF Teleconverter works with any lens, not just A/F/FA/DA ones. It will work with M and K lenses. Yes, it even works with M42 screw mount lenses.

In order for the autofocus to work with the M42 lenses, you need to put a little piece of aluminum foil between the base of the lens and the electrical contacts on the converter.

I've gotten mine to work with my Super-Takumar 300/4 in moderate light. I don't have anything slower to test it out.

The only 'bug' I've found with it is that it doesn't calculate the aperture correctly with the A 50/1.2 when wide open. Every other lens I own is fine.
08-22-2007, 04:58 AM   #6
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QuoteOriginally posted by Khukri Quote
Thanks, Wim!
Hope all is well with you; I forgot you used to have one!! Infact, you should be the right person to ask - will it work on the 100mm f3.5 you sent me? Did you try them together? What should I do to get the lens+1.7x combination to AF if, say, the subject is 1 metre away from the lens?
The very best!
The neat thing about the 1.7x AF Teleconverter is that you 'pre-focus' and then the converter has a small range to adjust. I usually focus the lens just in front of the subject and let the converter finish the focus. It should work with an f/3.5 lens just fine.
08-22-2007, 05:58 AM   #7
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QuoteOriginally posted by Khukri Quote
Thanks, Wim!
Hope all is well with you; I forgot you used to have one!! Infact, you should be the right person to ask - will it work on the 100mm f3.5 you sent me? Did you try them together? What should I do to get the lens+1.7x combination to AF if, say, the subject is 1 metre away from the lens?
The very best!
I'm fine thanks! Hope the FA100/3.5 made it all right?

I didn't use the two together. I believe I tried the Tamron 1.4x once, but I cannot be sure. f/3.5 being only half a stop from f/2.8 I guess it should work more or less OK.

Personally I never AF for macro subjects, I find MF much easier. Though at one meter it should be OK. As posted by carpents, you can even focus the lens closer with the 1.7x than indicated by the minimum focus distance. I guess setting the lens manually at 1m would give the TC the freedom to fine tune focus around that distance?

At infinity it won't focus at 1m, the 1.7x's AF range is much shorter (starts further from the lens) than the range of the lens without it when the lens is focused at infinity. But manually focusing it closer by actually yields a larger range, though never in one go if you see what I mean.

hth, Wim
08-22-2007, 10:14 PM   #8
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Dear Carpents & Wim,

Thank you for your advice. Shall try it out with the 100/3.5 and see how well it works!

Carpents, what sort of image quality do you get with your 300 Takumar + the 1.7x? And how effective is SR with this combination?

I am wondering whther someone here can or has compared the efficiency/effectiveness of a Canon 300/f4 IS with that of a Pentax 300/f4 on a K10D. (With and without the TC.)

Thank you!

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