Quote Originally Posted by sedwards View Post
If i have a crop sensor and shooting 300 mm is 1/320 shutter speed my minimum or hould i multiply by 1.6?
As others have said, non-IS rule of thumb is 1/EFL, so in your case EFL = 300 * 1.6 = 480, so ideal shutter speed is 1/480th, aka 1/500th.

With an early-edition IS lens capable of 2-stops IS, rule of thumb is 4/EFL, or 1/125th if we're talking about 300mm.
With a middle-edition IS lens capable of 3-stops IS, rule of thumb is 8/EFL, or 1/60th for 300mm.
With a recent-edition IS Lens capable of 4-stops IS, rule of thumb is 16/EFL, or 1/30th for 300mm.

There's a shot in my personal favorites bin that's EFL of 260mm, and shutter speed of 1/13th, subject ~1.25 miles away, solid as a rock. I got lucky that night, though I give the lens lots of credit too.