Originally posted by dirwood I think I got it narrowed down now. I am going with a zoom lens for now so the DA* 300 is out. The TC options are the 1.4x and 1.7x. Is there any difference between the 2 or are they equally as good and one just has longer reach?.. Will Sigma zoom lenses work as good as the PLM lens with the TC's.
This is pretty much what I'm down too without trying to spend more than 1k.
I've no experience with either of those two tele-converters, but I do use a Kenko 1.5x as needed. I also use a Sigma 150-500mm almost exclusively for birding. So, in that context, the KP
can start to struggle with the tele-converter fitted to the Sigma. It's fine in good light on a static subject … AF/S and go for it … it'll probably take a moment or two to "lock on" but it'll work. Tracking a moving subject, except against a clear sky, is a bit more of a struggle, though the latest firmware does seem to improve things in this respect. This is all (probably) due to the Sigma's maximum f/6.3 aperture effectively becoming around f/9.5 with the converter fitted, well outside of the recommended (if conservative) f/5.6 minimum for reliable autofocus.
Extrapolate from these experiences what you will … a 500mm (with a useful "trombone" zoom action, great for initially finding your subject in the viewfinder) which isn't totally reliable with a converter fitted, or a shorter, wider aperture lens, which is likely to work better with a converter, but doesn't have the initial reach
The other factor to consider when using a converter is that, with the Kenko at least, the camera isn't aware of the converter, so continues to generate EXIF and configure the Shake Reduction for the native length of the lens … just when you need all the help you can get
Good luck and enjoy