I am taking a photograph course and the instructor, who repairs cameras, says it is extremely important to turn off the Image Stabilization on the lens before you remove it from the camera. He says turning it off "locks" things in place and prevents damage. Is this true? I have googled it and can't find any reference to this. I have a Canon 20D and Canon lenses. Thanks!
the only time the IS elements are "moving" is during the focus process (when you have your finger on the shutter button and a couple seconds after) otherwise everything is locked in place. If this weren't true then moving the lens and camera with IS turned on would have the potential to damage the elements of the lens and that would defeat the purpose of the IS in the first place.
Your instructor is wrong.
[Edit] from the EF 100-400 F4.5-56L IS USM manual (page E-9):
The image stabilizer continues to operate after you release the shutter button, as long as the metering timer displays the exposure value. Never remove the lens while the image stabilizer is operating, or you could damage the lens.
This is incorrect. Modern image stabilization is achieved through a lens element that is moved via electromagnets. Since electromagnets need to be powered in order to work, removing the lens (and the power source) will effectively lock the element in place rendering any movement impossible anyway.
Having said that, there are a number of really 'old school' lenses that potentially would be damaged if the image stabilization was not turned off first because they used gyroscopic stabilization methods instead of electromagnetic ones and the 'off' button literally locked physical elements of the lenses in place. Not locking the elements meant that they just 'rattled around free' in the lens housing. You don't have one of these lenses, however... They wouldn't fit on your Canon 20D (or any other modern camera)!
Not trying to judge, but this may be a case of an instructor not bothering to learn about new technology advances and carrying forward bad advice because "that's the way it used to be," which sadly happens quite a bit...
From Roger Cicala's blog at lensrentals.com describing his teardown/comparison of the insides of the EF 70-200mm f/2.8 L IS II versus the EF 70-200mm f/2.8 L IS III:
Looking from underneath, though, you can see the plastic posts that we sometimes mention. These occasionally break, possibly from shock during shipping. If the IS is not turned off, the lens group is free to bounce in all directions with only the posts to stop the motion.
Both the version II (2012) and version III (2018) of this lens are identical in this respect.
Just because IS is not active and moving the gyros and stabilising elements does not mean the inner half of the IS unit is not free to flop around inside the lens.
Later in the comments section of the lensrentals blog entry Roger responds to a question from a reader and says:
The proper thing to do is 1) Turn IS off at the lens while the lens is still mounted to a camera. This 'locks' the IS unit in place. If you have IS on and just remove the lens from the camera, then it does not lock and off the camera flipping the switch does no good.
You can confirm by gently shaking the lens; there's very little noise if the IS is locked.
The locked position is safer for transporting the lens. If it's not locked the IS unit can bounce around and cause damage. How big a deal is it? I can't say for sure, but maybe 1 in 1,000 shipments that come back with IS not locked are damaged. But the incidence is 0 in 1,000; or very close to that, with IS locked.
Yes. We do it with every one. The most obvious 'rattlers' are the 70-200 f/2.8 and 100mm f/2.8 IS, but it's good practice. We think it's so important that it's checked twice: once when it returns from rental, and as the last check again before it's packed for it's next shipping.
That being said, damage to the IS isn't frequent even if it's left off (for example, most customers ship them back unlocked), perhaps 1 in 1,000 shipments, maybe less. But for us that can mean several broken IS units a month.
If Uncle Roger says it's safer with Canon lenses to turn off IS and therefore lock it, I'm turning my IS lenses off before putting them away in my bag or case. YMMV.
Modern lenses are designed to be "idiot proof," else they generate too many returns and warranty repairs. It's a bad idea, but I have seen (and even done, on occasion) lens changes while the camera is on with no ill effects. Image stabilization doesn't need to be turned off on modern lenses (unless specifically stated in the documentation).
Panasonic released a Micro 4/3 macro lens last year that even rattles when not on the camera. Panasonic sent a notice saying not to worry, this is normal.