I'm considering purchasing a Kenko 1.5x TC to go with the Sigma 135-400 APO zoom I recently won on eBay. I've read various (conflicting) comments on performance and wondered if anyone had any experience with this particular TC.
My main concerns are optical performance and retaining AF with the Sigma zoom.
The Sigma 1.4x EX TC will not work with this lens due to the position of the lens rear element. Any advice, comments or alternative recommendations would be much appreciated.
I have got one of those converters. The instruction manual says that the
lens needs to be f:4 or faster to keep AF. In practice, AF works also
with an F* 300 mm. 4.5, in bright light conditions. But AF isn't only lens dependent, it also varies from camera to camera. For example, if I use the F* 300 mm. + 1.7x Pentax AF converter on my Z-1, AF doesn't work in any circumstances, but the same lens plus teleconverter on the MZ-S autofocuses very well.
On the optical side, the Kenko is OK, but don't expect it to be as good as the Pentax 1.7x AF or Pentax 1.4-S. With the Kenko you'll soon notice some loss of contrast (not much), when compared to the original lens without the converter, and sharpness will also be slightly reduced.
Carlos
