I have a canon 60d, Canon EF-S 17-55mm f/2.8 IS USM lens, and a Canon Speedlite 430EX II TTL flash. I like to use the manual modes, such as Av and Tv but I am having some difficulties when using the flash. I notice that when I use the flash in auto mode I get much better ISO performance. For example this morning I performed a few test shots of my remote control for the TV. In Auto mode the camera shot 1/60 at 2.8 using 1600 ISO. When I put the camera in Av mode I was only able to get 1/6 at 2.8 using 1600 ISO. If i wanted around 1/60 shutter I would have to put the ISO up to 1/6400. I am unsure why this is true. Does anyone have any ideas or suggestions?