When I might want the flash I know how to get it. But I almost never use it.
The Canon PowerShot S50 has a way to save your settings in C mode. With that I never had to worry about the flash--I had it disabled and saved that way.
Don't see a way to do this with the EOS XTi. Seems you just have to remember to press the flash button on the side and even then I'm not sure it'll stop the flash. I see ways to save in the P mode and others, but not a way to make sure that flash won't fire.
I'm sure there's something I'm missing. 
Please let me know. Thank you.


