Canon Rebel T2i Quick Start Manual page 34

When to change shutter speed:
• I only recommend deviating from the rule of the shutter speed
remaining twice the frame rate in the following situations:
• One: You are outside on a bright day, you are already shooting at the
lowest ISO possible (100 ISO), at the smallest aperture opening
possible (f32) with image compensation and the image is still
overexposed! In this case, increasing the shutter speed to a higher
number will cut light and decrease exposure. A better option is to use
an ND filter (not included in this kit).
• Two: for a special motion effect.