ct1co2 wrote in post #18912103
One of the key benefits of IS I appreciate for telephoto use is it settles down a wobbly viewfinder. If I am focused on a subject waiting for something to happen, I am mostly handheld, and I am unable to hold perfectly still. Although the shutter speed negates the need for IS many times, it helps me with framing, composition, and not getting dizzy looking through the viewfinder.
This is the real world benefit, to me, of IS; if I'm shooting, say, an airshow, it is much easier for me to acquire the incoming aircraft in the viewfinder and keep them there as I pan with them when IS is engaged. This also means I'm able to use slower shutter speeds to catch the jets than I would with a non-IS lens (1/400 to 1/800 is usually where I'll shoot) and also makes it a bit easier when I'm trying to slow things down to catch the prop planes without freezing them. Camera shake still hits the final image and I have to work to reduce that physically; but the framing and tracking is much simpler.
Also, whether primary usage will be from a tripod. For example, shooting the moon, I will start with IS on to frame and zoom in on the silly disk and then switch it off and give the setup a few seconds to settle, then do the actual shooting with IS disengaged, since the action of settling the IS lens group can actually cause motion blur in this type of application.