Question about ISO

I like not to use flash if possible but my model (14mo) is moving fast so the exposure time needs to be short. What would you consider too large ISO? I have rebel so I can only choose 100, 200, 400, 800 and 1600. I try to do 400 or less but sometimes have been using 800. I'm too afraid to even try 1600, do you use it?

800 and 1600 create a lot of graininess. I personally wouldn't go above 800 at the MOST. I usually use 400 and try to use my 50mm that handles light better and open up the aperture wider to let more light in.

with the rebel I wouldnt go over 800 either... unless you're really good at photoshop and filter out the graininess....if you get a better camera...the performance on higher isos is better.

I agree--but you can usually still get away with using 800 (some cameras have less noise than others). BTW, what's this about being able to reduce it in Photoshop? Can someone please explain how????