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I just bought a D3100 and started reading its manual. On the lens' Vibration Reduction chapter it said that the VR should be turned off before turning off the camera, every time I use it. Is it really necessary? Why?
I think the manual said it had to do with the lens stability, after the camera is turned off...
It depends on the lens, but it's a god habit to get into. Doing a "safe shut-down" ritual on a lens that doesn't need it has far fewer consequences than skipping the step on a lens that does.
In-lens optical stabilisation systems work by floating one or more lens elements under the control of servo motors. While VR (or IS, or whatever the brand name is on your camera) is active, there is no firm mechanical connection between the lens's stabilisation element(s) and the body of the lens -- it's essentially free to flop around inside the body if the motors aren't running. If you shut off stabilisation on the lens while the camera is still powered up, the element is returned to a neutral position and mechanically locked in place. If you don't, then the lens is still free, but there's no longer a motor to keep it in place.
Not only does that mean that the lens is less delicate to transport, it also means that if things go wrong and the element gets stuck, you're left with a non-stabilised lens that has all of its elements centred. If the element were to become frozen somewhere outside of its normal range of controlled motion, you'll be left with a lens that is visibly degraded; softness and vignetting will be centred around the lens's optical center, which will no longer be the centre of the image. In other words, you'll have a lens that makes really nice pictures only if you keep the subject, say, left of centre in the image.
I remember a time when we had to run a head-parking routine on hard disk drives before shutting down a computer. It wasn't always necessary, but if the computer were bumped or moved with power off and the heads unparked, there was a good chance that you'd lose your disk. Modern drives (basically everything made since 1993 or so) autopark the heads -- the "park routine" is just a spring, so you don't have to use the motor to move the heads to a safe position. VR/IS lenses will probably be the same as time goes by -- but it's the lens you're using, not the camera, that determines whether you need to let the stabilisation system centre under power or not.
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.
In a DPReview forum discussing Roger's Blog entry, Roger answered the question, "Roger - would that be the best practice for ANY Canon lens with IS? Turn off IS, then remove from camera?"
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.
