Can I use my old Canon Speedlite 166A with a Powershot G6? If yes, would it be appreciably better than built in flash? Thanks.

I'm not familar with you equipment but if you use a flash unit that has a "high voltage trigger" with a digital camera, you will ruin the camera Check with flash manufacturer.

The 166A was made for the old A-series Canon SLR cameras (A-1, AE-1, AE-1 Program,...). I think it is probably safe to use with EOS and the G-series digicam, but it wouldn't hurt to test its trigger voltage. If you don't have the user manual, it is available at <a href="http://66.49.230.119/flashes_meters/speedlite_166a.pdf">http://66.49.230.119/flashes_meters/speedlite_166a.pdf</a>. It should work the same way with the G6 as it did with the A-series bodies (ie. manually match ISO and aperture settings on the camera and flash).