Originally posted by retired2007 here's what i have , a k1 with the 70-200 2.8, i also have the old 55-300 which on a clear day is a great lens. i have a k20d that i am using the 55-300 on and it just isn't there . would like the converter for both the k1 and am looking in to a k3ii.
I assume you mean the DFA 70-200 f2.8? That one uses DC autofocus, rather than screwdrive. I tried my DA 18-135, which also has DC AF, with the Kenko (with the pz contacts) and it does work. I'm not sure that a TC without the pz contacts will work with any AF lenses other than ones with screw-drive AF. Other people will be able to confirm that.
As for the 55-300, the screw-drive versions (not the PLM version) will work with any AF TC. But you need to bear in mind that a 1.4x TC will cost you one stop of light - so the maximum aperture of f5.8 at 300mm becomes, in effect, a little narrower than f8. Not to mention that that lens benefits from stopping down, especially at the long end, so you may need to be somewhere in the region of f11 or so. And if you are using it for moving subjects like birds, where faster shutter speeds are also required, you will need good light to allow these settings. (Maybe the K-1 would be better than the K-3 series in this regard, because of its superior high-ISO performance.) On most cameras the autofocus is likely to be unresponsive or hit-and-miss at such narrow apertures when the light is less than excellent. And of course a TC is only as good as the lens it's used on - I also have the 55-300 and while it's very good for a consumer zoom, it's no match for my FA*300 f4.5. Personally, when it comes to using a TC with the 55-300, I wouldn't find the game worth the candle.
Nevertheless, a number of people have successfully used the 55-300 with a TC. If you search the forums you will find plenty of examples. By all means try it, but don't expect it to work well every time.