boberic wrote:
Is IS obviated by fast 1/400 shutter speed, and therefore might as well be off?
The short answer, in my opinion, is "No".
And it's way too simplistic to try to choose a set shutter speed where IS may not be needed. It depends upon and varies
widely with lens focal length and/or magnification... camera sensor format... user skill, capabilities and technique... as well as the local conditions while trying to get a "steady shot". For example, a long telephoto like a 600mm might call for 1/600 on full frame or 1/1000 when used on an APS-C camera or even faster shutter speed if used on smaller formats such as micro 4/3. In contrast a 24mm lens might be hand-holdable without IS at 1/25 on full frame or 1/50 on APS-C, etc. There's also a big difference between shooting while standing on a concrete slab versus shooting from the deck of a ship... or, for that matter, from any vehicle with a motor running.
The long answer is...
I've been using Canon Image Stabilized lenses for over 15 years, have shot hundreds of thousands of images with them, and currently have nine Canon IS lenses in my kit.
In fact, one of the main reasons I switched to the Canon system in 2000/2001 was because of IS. No one else was offering any form of stabilization at that time and in my opinion it was game-changing technology. Canon IS certainly proved to be successful... Enough so that almost every other camera and lens manufacturer had to follow Canon's lead and now have implemented some form of stabilization too. They were about ten years behind Canon, but it's a pretty level playing field now. EXCEPT that each manufacturer's stabilization system is patented, so there's no doubt some differences between them.
I virtually never turn IS off. Sometimes I'm sure it's not serving its primary purpose because I have a plenty fast shutter speed. But it also doesn't do any harm to leave it on (and, seconds later I might have followed the same subject into shadow where a much slower shutter speed will be used). When I experimented with using IS on and off (many years ago now), I saw no change in image quality and very little difference in battery usage. I saw I was getting a lot of help from IS... It improved the vast majority of my images... Especially when I was still shooting films that were ISO 50, 100 and 200 at the fastest most of the time, only occasionally and reluctantly ISO 400.
I also noticed early on that IS also helps stabilize the image in my cameras' optical viewfinders, which can be useful at times when panning and tracking moving subjects, especially with long telephoto focal lengths. In this case, shutter speed is irrelevant.
Further, I have no way of proving it, but I think Canon IS helps autofocus perform better. It makes some sense that a stabilized image would be easier to lock onto (but this pertains to Canon IS
only.... seems it isn't the case with all stabilization systems... see below).
Out of thirty or more lenses with it, there are five Canon IS lenses that use a system that needs to be turned off at the switch when there's no camera shake occurring, for the IS to correct. Often people refer to turning it off whenever using a lens "on a tripod". However, not all tripod use fully eliminates all camera shake (IS can even be effective counteracting internal camera vibrations such as "mirror slap" in SLRs). Plus, there can be situations where there's no movement for the IS to correct, even when not using a tripod. Many Canon lenses "self detect" lack of movement and automatically turn off IS when it's not needed. The ones that don't and have a problem include the original EF 75-300mm IS USM (1st lens to have IS, around 1995), EF 28-135 IS USM, and original EF 100-400L IS USM "push/pull zoom". Not officially on Canon's list, the EF 24-105L IS USM (original version) also seems to show similar effects. All four of those lenses are discontinued and/or superseded by new models that do not have the same problem. The 5th and only lens on "the list" that's still in production is the EF 300mm f/4L IS USM. I've used four of these at times and extensively use multiple copies of two of the lenses on this list and have to note that all of them are designs that especially lend themselves to hand-held use.... At least that's the way I've used them.
What happens with those particular lenses' IS when there's absolutely no movement for it to correct, is that the stabilization systems goes into sort of a "feedback loop", where it's actually creating rapid movements that can effect images. The good news is that if this occurs, you'll see it happening in the viewfinder and that will remind you to turn off IS... no harm done. The worst that can happen is some images with movement blur.
Other Canon IS lenses do not normally show this problem. They turn IS off themselves. However, some other times when you might want to turn off IS are when making videos and if shooting an image that requires very precise framing. This because IS often has some slow "image drift" (not to be confused with the rapid movement the above lenses). Also, IS makes some slight noise which may be picked up in the audio of a video.
Canon lens user manuals all tell you to turn off IS when the lens on a tripod. However, Chuck Westfall, Canon USA's tech guru, told me that was primarily suggested to save battery power. Again, I don't think IS draws very much power. I often shoot with a pair of cameras, one fitted with an IS lens, the other with a shorter focal length, non-IS lens. After a long day's shoot I get nearly the same shots per battery from both cameras.
IS is now on many lenses in the Canon system. Originally it was implemented mostly on telephotos where it's probably the most helpful. But it now can be found on much shorter focal lengths such as the ultrawide EF-S 10-18mm and EF 16-35mm f/4, as well as standard zooms such as the EF-S 17-55mm and EF 24-105L II, and even on some primes such as the EF 24mm f/2.8 USM, 28mm f/2.8 USM and 35mm f/2 USM. On these lenses, IS may not be as much of a "game changer" as it is on telephotos. But certainly doesn't hurt either!
Early Canon IS lenses offered 2 to 3 stops of assistance. Newer ones offer 3 to 4 stops, according to Canon.
Some Canon IS lenses have user selectable "modes". Standard IS "Mode 1" counteracts movement both on the vertical axis and the horizontal axis. "Mode 2" is intended for panning, when you don't want IS to counteract motion blur effects in one axis, so it only provides correction to the vertical axis (note: camera orientation is sensed, too... so that single-axis IS is correctly applied regardless). Some of the most recent IS lenses have a "Mode 3" too, which is sort of an "instant stabilization". In this mode the IS is only applied
during the actual exposure... which suggests that IS in these lenses is extremely fast acting. (I only use one lens with Mode 3, so am not all that familiar with it yet, but after 2 years it seems equally or more effective than older versions.) Other recent Canon lenses automatically detect panning and self-activate a "Mode 2", without the user having to set anything.
None of this should be interpreted as applying to any other manufacturer's stabilization system. The above applies to
Canon IS only and, even though the purpose is the same, I'm certain there are differences in how the stabilization systems of different manufacturers perform. Canon, Nikon, Sigma, Tamron and to a lesser degree Sony all produce lenses with optical stabilization. Pentax, Olympus, Fujifilm, Panasonic and to a large extent Sony instead produce DLSRs and mirrorless cameras with stabilization provided by moving the camera's sensor itself to counteract shake. There are some minor differences, but both methods accomplish what they're supposed to do.
A more specific example of some differences... Nikon users often suggest that VR should be be turned off when possible because it seems to slow autofocus slightly. At first I though this might be "sour grapes"... Long time users of Nikon gear justifying why they stuck with the brand for many years when they didn't have stabilization, while Canon kept introducing more lenses with IS. But there seems to be some evidence to support this. However, it's just the opposite of what I think occurs with Canon IS... that it helps autofocus perform a little better.
Other manufacturers' stabilization systems are bound to be unique and each have some nuances of their own. I can only say I've heard that Sigma and Tamron's are very good, roughly equal to Canon's. Sony combines lens-based and camera/sensor-based stabilization to claim some extra high performance. There's talk of systems that apply correction to 3 or 5 axes (horiz., vert., near, far, and yaw). In a sense, continuous autofocus itself can provide some near/far correction (for this reason Canon increased the distance sampling frequency of the AF systems in some cameras by 4X, when those cameras are fitted with OEM macro lenses).