I've been trying to wrap my head around this, and I think it's fairly obvious but I can't pinpoint why. We all know the general "rule" of setting your shutter speed to the equivelant of your focal length (i.e. a 200mm lens should be at least set to 1/200sec) to essentially freeze action. So let's say you have an 85mm & a 300mm. Given a moving object that stays constant from the lens, I would assume the 85mm set at 1/300 freezes the action better than the 300mm set to 1/300. If we say the 300mm is 353% "larger" than the 85mm, does that mean the 300mm should be set to at least 1/1000 to have the same frozen action? Sorry if this is confusing' that's probably why I can't seem to logically piece it out.