Opinions of 1.5x,1.7x,2.0x AF teleconverters

[Reportage]

planning to get one to extend the range of my tamron 75-300 zoom.

so far pentax`s is still MIA so left Kenko and so on.

are there any NOT recommended models to look out for?

Which TC`s the AF actually works as advertised?

 

[longko]

IIRC, 2 most after AF TC are Pentax-F 1.7x and Tamron-F 1.4x Pz-AF MC4.

 

[adiknaim]

TC coupled wif ur tamron... aperture will be very small eh.... n i tink most TCs dont AF if the aperture is smaller than a certain value rite? i tink so la.. haha.. wait for other pros to comment...

 

[Gengh]

I've used Kenko's Pz-AF 1.5x Teleplus MC with the Tamron 70-300mm before, the AF works perfectly fine even at 300mm despite the small aperture, but the IQ leaves very much to be desired. Point to note: if you want to use SDM lenses with a Kenko 1.5x Teleplus, you need the SHQ version. The MC version can't AF with SDM lenses, and I've no success even after taping up the SDM contacts (which were meant for power zooms).

For your reference:
http://photo.net/pentax-camera-forum/00SfYS
http://www.stevesforums.com/forums/view_topic.php?id=601814&forum_id=94&jump_to=961195
http://www.pentaxforums.com/forums/pentax-slr-lens-discussion/18264-teleconverter-question.html

Edit: Should probably add that I was using K100D body, and in overcast, but still fairly bright, conditions.