Canon EOS - Erin Manning about the Rebel XSi / EOS 450D / Kiss X2 4/6

[c2thew]

you don't have to turn off the camera to change lenses. also, instead of using a timer, you can use the built in 2 second shutter delay in your camera. this only applies if you are doing bracketed shots, or shooting at night. also, use f/8-f/13 if you want as much as possible to be in focus. if you stop down the lens too much (f/22) you encounter diffraction, which means that the lens can't resolve the detail in the image, leading to softer/less sharp image.