philwillmedia wrote in post #10631512
If you think about it logically, the IS is trying to do something it's not designed to do.
The IS detects the movement of the subject and thinks it's movement of the camera body so is constantly trying to compensate for something it can't.
Put simply IS cannot stabilise a moving subject.
IS systems do not, cannot, and are not designed to compensate for a moving subject. They're a gyroscopic mount in the lens that detects motion imparted to the unit and attempts to cancel it out by shifting the element(s) of the lens to dampen the motion.
Frame a stationary object at, say, 400mm on your 1-4; notice how there is some "sway" as you try to steady the lens. Now, give a half press of the shutter button and wait a couple of seconds; notice how the image doesn't bob around as much. That is all IS does, regardless of your subject's motion or lack thereof.
I think the Mode 2 IS concept is a confusing one for folks, since it's recommended for panning on moving subjects. But it is still irrelevant to the subject itself; Mode 2 simply disables the IS system from caring about horizontal movement of the lens so that it doesn't try and correct for left/right panning.
And to the OP: Needed? I hardly think one could claim it was *needed*, as a blanket statement. If you're shooting at the higher shutter speeds (1/640 on up) then it's likely not doing too much for a shooter with a solid stance and technique. *I* won't buy a lens without IS because I don't have the fine motor control to truly hold one of those steady, so I "need" IS. Plus, when shooting some action, I like to pan and drop the shutter speed fairly low (prop planes, 1/200s @ 400mm, for example). IS makes that much easier.
