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12-21-2010, 10:45 AM   #16
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QuoteOriginally posted by jwblilie Quote
Thanks for all the info. I'm mulling all the options. I will probably get the PENTAX 1.7 AF, since they are still readily available. But I'll keep my eyes open for the KENKO and TAMRON ones as well.

Lowell: Thanks for the link! Very helpful!
Note that the .7x TC will cost you 1.5 stops so make sure you are faster than F6.7 combined or AF will still be an issue

01-05-2011, 01:40 PM   #17
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I ended up getting the PENTAX 1.7 AF

I ended up getting a PENTAX 1.7X AF converter (but I haven't had a chance to try it yet!)

I'm going to try the SIGMA if I can ever get my hands on one ...

I feel pretty comfortable with PENTAX glass. And the positive reports from others on this site makes this unit seem like the best choice (PX 1.7 AF).

Thanks all!
04-08-2011, 12:45 PM   #18
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I recently purchased (from B&H) the Pentax DA* 300mm f4. I love the lens but am still interested in extending the range a bit. I have a Kenko 2X MC7 telextender which does not work at all but was wondering if a 1.4x (or1.5x) might work. Does anyone know if the Vivitar 1.4X will work on this lens?
04-08-2011, 01:14 PM   #19
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richard

you need to check if the TC you are looking at has the power zoom contacts, i.e. is a KAF2 mount or specifically says PZK or something like that on it,.

Not all teleconverters have these contacts and without them there is no chance at all of it working (other than manual focus)

a 1.4-1.5x TC will be fat enough (assuming electrical compatibility) to permit AF, where a 2x wont

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