Marsu42 said:
Mt Spokane Photography said:
IMHO, you are much more likely going to break something turning that switch off and on.
Do you have any data on this? Personally, I wouldn't be so sure and thus keep "protecting" my IS if the shutter time doesn't warrant it at all. Plus the 100L IS sometimes makes frightening noises when I turn it on with the camera in a near vertical position (*kneeeecchh-eeeeeek!*) but as far as I've read this is to be expected on this model.
Of course, there is no published data.
One of my engineering specialties, however, is switches. They are difficult to produce with a long life, and are rated for numbers of actuations. OEM's select a switch for its expected usage to save $$$ and to reduce size of the switch.
The IS switches are not intended to be turned on and off thousands of times. In a lab, you could probably actuate them a million times, but in the real world, dirt and dust accumulate in tiny amounts, and some will make it past the seals on the switch as it actuates. This shortens the life by a big factor. The switch covers themselves also fall off. Replacing a IS switch is expensive, because they are typically mounted to a circuit board and you have to replace the entire switch assembly which usually means all of the switches, which is going to cost more than you'd think. On the other hand, the IS system is designed to be used over many years, and using it does not bring in dust from the outside. The IS is pretty fragile, most damage is from bumps or drops.
Using IS at very high shutters speeds can result in blurry images, but I've never had one that I could attribute to the IS. Its one of those things that is possible, but not a major issue.
I'm forgetful, and I might get more blurred images from not turning it back on when a slow shutter speed was used.
There is nothing wrong with turning IS off and on, but I'd not recommend doing it frequently, like 1000 times a month. which is ~ 30 times a day. Twice a day is only 730 times a year, so that should not be a issue.