Sans Mirror  

Back when sensor-based image stabilization—often referred to as IBIS (image sensor based image stabilization)—first appeared, there was an Internet frenzy over which was better, sensor-based or lens-based shake reduction. Marketing departments at camera/lens companies with vested interests in one answer or the other all fired up their mimeograph machines—uh, I mean marketing teams—and generated a great deal of contrary and confusing "information."

It's way past time to try to present a sane, reasonable explanation of the benefits and drawbacks of each type of image stabilization (IS).

But first, here is something you need to know: IS does nothing for subject motion. Nothing. The Internet myths you might read such as "four stops of IS equals one stop of aperture or ISO" are something you need to just learn to ignore. If you need aperture (and ISO) to get a usable shutter speed to stop motion, you need aperture (or ISO to change shutter speed). Period.

At the other end of the spectrum, at high shutter speeds most IS systems at some point start to take away a bit of edge acuity. Why? It has to do with the frequency of the data sampling and the movement speed of the physical system versus how fast that shutter is moving (mechanical or electronic). For years I've been warning people to turn VR off—Nikon's form of lens-based IS—if you're photographing at high shutter speeds. Currently I assess that to be faster than 1/1000 second. 

So image stabilization is a bit like antilock brakes on your car: when you need it, it's very useful. But you don't always need it.

Okay, so what do IS systems actually do? They do an excellent job of removing human-caused camera movement during an exposure. Sometimes wickedly so. I've handheld an OM-1 to one second and gotten a very usable shot of static subjects. IS systems also do a reasonable job with mechanical motion and vibrations. I've been rocked by boats, planes, trains, and more with wicked vibrations and bounces and gotten excellent images. I've had stadiums (stadia?) literally bouncing under my feet from fan excitement and still pulled off a sharp photo. 

And, of course, as I get older, it's gotten more and more difficult for me to hand hold slower shutter speeds without seeing some impact. Whereas I used to be very comfortable pushing 1/15 handheld without IS one moderate telephoto lengths, now I'd say that 1/30 is my limit, and I try to stay above 1/60 if I can. 

Lens versus Sensor IS

Okay, so there are times when IS is useful. Should you get sensor or lens IS? Note: since I originally wrote this article, most of the makers are now doing both for long telephoto lenses. More in a bit.

Well, both approaches have their pluses and minuses. You should also note that the smart bet these days are on dual systems, which use both approaches. There's a reason for that. 

A lens-based IS system generally is placed near the optical center of the lens (entrance pupil). The reason for this is that you get maximum shift ability with a reasonably small element(s) and movement of it(them). The smaller the mass, the faster you can move it, and with less force (F = M*A, remember that formula?). Less force also means you don't need strong motors that use a lot of power, so the lens-based systems have tended to be reasonably kind on camera batteries.

Lens-based IS is helpful where the entire system (camera+lens) is rotating in its movement. The longer and heavier the lens, the more likely that the fulcrum point of motion is well forward of the camera body; but that's why the lens systems put the IS system at the fulcrum point: you easily get the maximal correction. Update: I tend to think the improvement starts to be clearly seen for lens IS over sensor as you near 200mm focal length (full frame). 

Moreover, with really long focal lengths, you are transcribing a very narrow angle of view overall. A 300mm lens sees about an 8° wide view. At a distance of 50’ (~15m) the field of view is about 6 feet (2m) on the long axis. I've seen people struggling to keep framing (and the focus sensor being used) within even a 6" side-to-side position on the subject, which translates to about 500 pixels on a 24mp camera. That's more than you can move the image sensor in any existing 24mp IBIS system I know of. Yet it is often within the range that a lens-based systems can deal with.

The problem with lens-based IS is that it adds cost and complexity to every lens. It also is restrictive in what it can steady. Vertical and horizontal shifts and rotations are easily handled by lens-based IS. Lens-based IS can't correct for camera roll, for instance, but IBIS systems can.

One reason why DSLRs don't have sensor-based IS is that this wouldn't stabilize the viewfinder prior to shooting, or the focus system. A lens-based IS system does. A stabilized sensor by itself wouldn't keep autofocus systems aligned to the subject (the DSLR focus systems are forward of the image sensor, so don't get the IS benefit). 

Mirrorless cameras, of course, use the image sensor to drive what the viewfinder shows and incorporate the focus system, so having on-sensor IS (again, typically referred to as IBIS, tends to mean that every lens you mount on the camera has some viewfinder stabilization active at all times (there may be some exceptions with adapted lenses on some systems).

The issue with IBIS is that it needs information about the lens to work correctly (thus the exception for some adapted lenses that aren't supplying the proper lens info). IBIS also has a modest range that it can correct, and it adds heat and mechanical complication at the most expensive part of the camera (image sensor). 

Finally, IBIS tends to not disrupt bokeh in out of focus areas as much as lens-based IS sometimes does. Lens-based IS tends to distort optical paths a bit if the IS element isn't perfectly at the entrance pupil, while IBIS does not have that issue.

Of those, the problem with IBIS that is most important to note is the range limitation. That's why Canon, Nikon, Olympus, Panasonic, and Sony have now all gone to hybrid systems with telephoto lenses. In other words, lens-based IS coupled with sensor-based IS. 

Olympus also still warns about sensor cleaning potentially damaging their IBIS system. (Early Sony systems were also easy to bust, but Sony later changed the design. Nikon locks down the sensor (except for the Zf) when the camera is off or in cleaning mode, though they also disclaim physical sensor cleaning by the user. Fujifilm users should always turn IS MODE to OFF prior to physical sensor cleaning.)

My big problem with image stabilization is this: some makers seem to be treating it as an "always on" feature. They often bury the only way to turn it on or off (or control other aspects of the IS performance) deep in some menu you'll not remember the location of. I disagree with that approach. I really want to escalate IS on/off as something I can get to without dropping into menus. As I hinted above, I believe that optimal image capture requires that you use IS conditionally, not all the time. 

CIPA Ratings

Should you pay any attention to the CIPA ratings for IS? 

Probably not. In practice, the CIPA IS ratings are just like the CIPA battery ratings: your mileage will vary. There's really never a dud in the bunch with CIPA IS testing, and any differences in rating don't typically speak to the more practical things you should be aware of.

For example, there is a difference between how well the various IS systems detect whether you're on a tripod or not—yet another reason why I want to take control of the IS setting—or whether you're panning with a subject and the stabilization should maximize a particular correction in that case. That's something I'm struggling to come up with a valid test for, but I do notice differences between the systems. My suggestion: turn IS off when the camera is on a stable support that’s not moving (e.g. tripod on solid ground), and learn whether your camera has a dedicated “panning mode” for IS and use that when panning. For instance, on Nikon cameras, the Sport mode is better for panning than the Normal mode. That's because the Nikon system is aggressive about re-centering the system on movement.

The Different IS Systems

Which brings us to this: 

• Canon IS— the RF cameras and lenses use both IBIS and lens IS. The older M cameras mostly used lens IS.
• Fujifilm OIS — a few bodies now have IBIS (e.g. X-H1, X-H2S, X-S20), some don't (e.g. X-T30).
• Hasselblad — no stabilization.
• Leica — no stabilization.
• Nikon VR — IBIS for the Zf/Z5/Z6/Z6II/Z7/Z7II/Z8/Z9, plus many adapted lenses have lens VR and the two work in conjunction. The Zf, Z8, and Z9 use something called Synchro VR when both lens and camera have VR systems. For the Z30, Z50, and Zfc, none have IBIS, but all the current DX zoom lenses have lens-based VR (IS using Nikon's vocabulary). 
• Olympus/OMDS IS — originally only IBIS, but now making telephoto lenses with lens IS that works in conjunction with IBIS.
• Panasonic OIS — originally only lens IS, but now making IBIS on most models (GH5s is an exception).
• Sigma OS — lens-based stabilization. May or may not work with camera's IS controls depending upon age of lens.
• Sony OSS — IBIS plus lens stabilization for telephoto lenses that works together.
• Tamron VC — lens-based stabilization. May or may not work with camera's IS controls depending upon age of lens.

All else equal, I'd rather have IBIS (sensor based) than not, but I want that to work with lens IS for telephoto lenses, particularly for lenses that are 200mm (full frame) or longer. Canon, Fujifilm, Nikon, Olympus, Panasonic, and Sony are now getting this (mostly) right, in my opinion. 

But I also photograph a lot with IS turned off, particularly when I ‘m using high shutter speeds (>1/1000 second). I prefer that IS be settable by an external camera control, not buried in the menus (Nikon gets this right, at least with lenses that have VR switches).