Canon G12 teleconverter
The digital teleconverter in the G12, works really well. Although you are limited to a 2mp file size, it does not suffer the deterioration of the usual digital zoom. Canon is using true sensor size to lens focal length conversion, by only sampling a small part of the sensor. Unlike digital zoom, which pixel bins the entire sensor to produce an allusion of true zoom, along with gross image deterioration.
If you will notice your entire focal range is moved up, just as if you had changed the lens, this does not happen with regular digital zoom. Which is nothing but an in camera crop, and up sampling of the image back to a larger format. Which produces quick image deterioration .
I have even used the teleconverter in my SX-150 up to 705mm, and printed a quite good 8.5 x 11 from it.
Cameras: Canon G12, SX150 is, and A1200.