Where Is IS?
The debate rages on concerning the best place to put “image stabilization” features. Is it within the lens housing, as Canon prefers; or is it within the camera body itself as Pentax, Panasonic, Sony, and others have adopted?
The big names in photography have evidently made their decisions, but photographers have their own opinions. As with most things in photography, if not in life, this decision is one with many trade-offs; if there was one completely correct answer, it would already be known.
Today I will dive into the briar patch and outline the pros and cons of both sides of the debate so that you can make a more fully informed decision about what equipment to buy.
What Is It?
First, let me explain briefly what “image stabilization” technology actually is. When you hold your camera in your hands, it moves around a little bit (unless you’re a robot, in which case I would like to meet you, please e-mail me). If your shutter speed is not fast enough (and you can use the focal length reciprocal rule to get an estimate of that), your photos can come out blurry due to this movement ((Robots take very clear photographs)). In order to help curtail the effects of “camera shake,” image stabilization technology was developed.
Canon and Nikon both use image stabilization systems that reside within the lens housing of particular lenses. In the Canon line, those lenses are marked “IS” (for Image Stabilization), and in the Nikon world they are marked “VR” (for Vibration Reduction). Both systems are based on the same fundamental mechanics; there is a small gyroscope or “accelerometer” inside of the lens that senses the direction and velocity of motion, and that sensor reports to a computer chip of some kind. The chip then tells a series of very small motors to move one or more optical elements around inside the barrel of the lens such that the image moves in the opposite direction of the motion. This is all explained pretty nicely on Nikon’s VR page.
The net effect is that the image seen through the lens moves considerably less, and when it does move it moves with an odd but strangely satisfying fluidity ((Note that this effect is only visible through the viewfinder when using in-lens IS, which is one of the arguments in this debate)). Canon and Nikon claim that using this stabilization technology will allow you to use a shutter speed one, two, or even three stops slower than usual to get a clear photograph. Numerous articles exist that test those claims, but I won’t get into that here.
Why Argue About This?
While Canon and Nikon have opted to place the image stabilization components in some of their (often higher-end) lenses, other makers such as Pentax, Panasonic, Sony, and others, have made systems that operate from inside the camera body. Rather than moving lens elements around, these systems actually move the image sensor itself. Canon explains this briefly in the Digital Rebel XTi Whitepaper:
Short focal length lenses require smaller sensor deflections; 24 or 28 mm lenses might need only 1 mm or so. Longer lenses necessitate much greater movement; 300 mm lenses would have to move the sensor about 5.5 mm (nearly 1/4”) to achieve the correction Canon gets with its IS system at the same focal length. This degree of sensor movement is beyond the range of current technology.
A bit preachy, but nonetheless true, is Canon’s statement that there is no technology available now that can move the sensor itself as much as 5.5 millimeters with the speed and accuracy necessary to make image stabilization for a 300 millimeter telephoto lens effective. That is one argument against the in-body IS systems out today.
Alright, so what are the benefits to having your IS system located inside the camera body?
You get some level of stabilization with any lens you use.
Lenses, in general, cost a bit less because you are not paying for IS mechanisms.
Stabilization becomes available with lenses that manufacturers might not deem worthy to have IS in them, such as short focal length and/or wide aperture lenses. These lenses may still benefit from some IS in extremely dark conditions.
I can think of times when even f/1.4 at ISO 3200 seemed like a mere pittance (such as in the aquarium), and IS sure would have come in handy then! On the other hand, there are downsides to in-camera IS, too:
Not as effective as in-lens IS because it isn’t tailored to any specific focal length or optics.
Ineffective after a certain focal length due to limitations in how much the sensor can be deflected mechanically.
The effects are not visible through the viewfinder. Because only the sensor moves, you can’t tell how well it’s working until you snap a picture.
An argument that I have often tried to make when this subject comes up is that in-camera IS puts you in greater jeopardy if it fails. While most serious amateurs carry at least a couple of different lenses, many can’t afford to carry more than one camera body, or simply find it inconvenient for most outings. Now, I don’t know what happens when in-camera IS fails, but the fact remains that you no longer have IS. However, if your in-lens IS fails, you can always grab the next IS lens in your bag (even if it isn’t ideal for your shooting situation ((Ideal would be having two identical cameras and two identical lenses, but few can afford that luxury)).)
It has been said that Canon (in particular, but this applies equally to Nikon) hasn’t implemented in-camera IS on its mid- to high-end models simply because they are already pulling in a lot of money from selling IS lenses. That may be true; Canon is certainly in business to make money, and they’re good at it, too. However, it is my opinion that in-lens IS, while potentially more expensive because you buy many of the same parts multiple times, and while potentially limiting because you only have IS in the lenses the manufacturer chooses, is superior simply because each mechanism is suited to the focal length and optics to which it is bound. This is confirmed by Canon in the same Rebel XTi Whitepaper,
With the optical IS used by Canon, each lens with IS has a stabilizer unit designed for that lens’s needs. The unit in a lens such as the EF 28-135 f/3.5-5.6 IS USM or the EF-S 17-85 f/4-5.6 IS USM is vastly different from the powerful, broad movement stabilizers in lenses such as the EF 400mm f/2.8L IS USM or the EF 600mm f/4L IS USM.
If you’re swinging an 18-inch-long 600mm lens around, in-camera IS just isn’t going to cut it.
Another viewpoint is that more IS cannot possibly be bad, so we should encourage manufacturers to place IS systems in their cameras and their lenses. I read this argument in The Online Photographer, and the writer, a Mr. Mike Johnston, makes a number of good points. I shudder to think what might happen with both in-camera as well as in-lens stabilization systems running simultaneously, but more seemingly insurmountable engineering feats have certainly been demonstrated in photography in only the past couple of years.
If anyone wants to comment on the other manufacturers' use of image stabilization or weigh in on which style of IS works best, just leave a comment.
As a wise man once said, “You shoot what you shoot.”