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07-17-2019, 01:44 AM   #1
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Kenko 2.0 Teleconverter issues

Hoping there is someone out there that has experience with the KENKO Pz-AF 2X TELEPLUS MC7 Teleconverter for PENTAX K-Mount. I just purchased on used and it wont focus it goes straight the focus point. I have tried it on my Pentax K3 ii with various Pentax and Sigma lenses in all AF modes but it is always the same.

Is there anyone out there that is successfully using such a set up?

If so was there anything you needed to do to get it working?

07-17-2019, 03:08 AM   #2
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QuoteOriginally posted by stewartvp Quote
Hoping there is someone out there that has experience with the KENKO Pz-AF 2X TELEPLUS MC7 Teleconverter for PENTAX K-Mount. I just purchased on used and it wont focus it goes straight the focus point. I have tried it on my Pentax K3 ii with various Pentax and Sigma lenses in all AF modes but it is always the same.

Is there anyone out there that is successfully using such a set up?

If so was there anything you needed to do to get it working?
It won't work with SDM lenses. It should work with screwdrive.

KENKO Pz-AF 2x TELEPLUS MC7 - SDM compatible? - PentaxForums.com
07-17-2019, 04:35 AM   #3
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QuoteOriginally posted by pschlute Quote
It won't work with SDM lenses. It should work with screwdrive.

KENKO Pz-AF 2x TELEPLUS MC7 - SDM compatible? - PentaxForums.com
Interesting, however one poster in that thread said given enough light AF work (although slowly) with one SDM Pentax and one HSM Sigma lens.

It could be the TC has a chip to compensate the focal length and aperture info as some of the Pentax TCs have. If the SDM/Power Zoom contacts are not wired up would be easy to test with a continuity checker or multimeter.
07-17-2019, 06:12 AM   #4
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the issue likely is that the combined native aperture of your lens plus TC is below F6.9 which is about the functioning limit of AF systems in general.

since you give up 2 stops of light, a 2x TC likely only works on lenses faster than F4 a zoom with maximum aperture of F5.6 for example becomes F11 and the camera cannot AF with such lenses unless in extremely bright conditions

07-17-2019, 07:33 AM   #5
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QuoteOriginally posted by Lowell Goudge Quote
since you give up 2 stops of light, a 2x TC likely only works on lenses faster than F4 a zoom with maximum aperture of F5.6 for example becomes F11 and the camera cannot AF with such lenses unless in extremely bright conditions
^^^^^ THIS!!!

What lenses are you trying?
07-17-2019, 08:12 AM   #6
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I think it should work in theory with SDM (the 1.4x Pz-AF does), but the 2x ones never work very well with autofocus -- just too much light loss. If your base lens is f/2.8 or faster it ought to work ok in bright light, anything slower it is going to be iffy.
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