Herb Chong asked: "since when isn't a pendulum an accelerometer?"
pendulum: A body suspended from a fixed support so that it swings freely back and forth under the influence of gravity, commonly used to regulate various devices, especially clocks. Also called simple pendulum accelerometer: An instrument used to measure acceleration a pendulum could be used to measure the acceleration due to gravity if an accelerometer were attached to it. The pendulum optical system in the Canon IS lenses works more from inertia than anything else. When the camera lens assembly moves the optical pendulum tends to remain stationary through inertia (and apparently some type of gyroscopic device(s)). The optical pendulum is designed to compensate for slight shifting of the lens axis. The above is based on the IS explanation in the Canon lens guide. An accelerometer based system would measure the camera movement and calculate the required compensation then servo motors (or some other type of device) would attempt to make that compensation. IMO that would be a mess. The Canon system is simple and elegant at the same time. I do wonder what sacrifices are being made in the design of the optics to make it work. I don't know if there is a difference in sharpness between IS lenses with IS turned off and non IS lenses. It would be interesting to find out. I have no idea how the Nikon system works. Tom Reese
