Tele-extender recommendations?
 

Any recommendations for preferred second party tele-extenders? I'm looking at getting a 1.5x for my wife's Canon digital Rebel to use with her Canon IS lens. It is not an L series lens so the Canon tele-extender won't work.

Which of the other brands (Sigma, etc.) would be a good choice?

There are several options in tele convertors. Sigma, makes a fair version and I would also look at the Tamron and Kenko 1.4x convertors. Most companies make at least two version. One, a more modestly priced model and the second a better, 7 element multi-coated version. Cheap convertors can really be a waste of money. The image degradation can be very noticeable.. If at all possible opt for the more expensive version.

There is one added feature of the off brand convertors. They actually focus faster than the Canon brand. Canon forces their convertors to focus slower, for what they feel is a more accurate AF. I have used both the Tamron and Kenko off brand convertors and feel the quality of build, optical performance are just below Canons. However, the faster AF is a nice plus. Try one out and see if you like the results.

Jeff, What sort of lens are you using your Tamron on? The local camera pusher in town said the IS doesn't work with the extenders. These people have been wrong before (more often than they have been right) so I wanted to check with someone before I got one for my wife for Christmas.

She has the Canon 75-300IS lens but not the 'L' series so she can't use the Canon extender.

I don't recommend 2x convertors, just too much loss of quality. However, most lenses can tolerate a 1.4x convertor. I have used the Tamron and Kenko convertors with several Canon lenses, including the 28-135mm IS and 70-300mm IS. If you keep the ISO low and print sizes 8x10 and less you should be fine. Never use a convertor on a WA lens. The 70-300mm IS is a little soft at the 300mm end of the range.