What's Shakin'?

Not your pictures, thanks to new image-stabilized zoom lenses from Canon and Nikon.

What-s-Shakin

What-s-Shakin

The way that image-stabilized lenses work sounds like something out of science fiction: Sensors inside the lens detect whether you're shaking, and which way. This info is transmitted in less than a blink to tiny motors that bend the light path to neutralize the shake. C'mon, admit it -- that's amazing.

Now the two original players in image-stabilized lenses, Canon and Nikon, have each introduced new optics -- both claiming up to a 4-stop gain in steadiness, instead of the usual 3 stops. So let's look at how well these latest blur- busters live up to their specs.

While both lenses are telezooms, and both can cover a full 35mm frame size, they are quite different designs aimed at somewhat different audiences.

The 70-200mm f/4L Canon EF IS lens is the Image Stabilized update of an existing lens that's been popular with photojournalists for its sharpness, constant f/4 maximum aperture, and relatively compact size for a rugged, metal-barreled lens. While the new version employs the same optical formula as the nonstabilized version, Canon says it has tweaked various elements to maximize image quality. As a Canon "white lens," it carries an appropriately hefty street price of $1,060.

Featured IS Lenses****Canon 70-200mm f/4L EF IS USM AF • Lens Test • Image Quality Gallery Nikon 70-300mm f/4.5-5.6G VR ED AF-S • Lens Test • Image Quality Gallery

In contrast, the 70-300mm f/4.5-5.6G ED-IF AF-S VR Zoom-Nikkor is an all-new lens that differs from existing Nikon zooms of the same focal length in both optical formula and physical construction. With a variable maximum aperture (ranging from 1/3 to a full stop slower than the Canon) and a good bit of polycarbonate in the construction, the Nikkor is a lightweight lens aimed at the serious amateur -- and priced accordingly, at $530 (street).

While Canon's Image Stabilization and Nikon's Vibration Reduction differ in a number of details, fundamentally they work the same way. A motorized lens group located about midbarrel can shift left/right or up/down according to the directions provided by motion sensors in the lens. As you view directly through the lens with an SLR, you can see the effect -- a slightly weird sensation at first. But most users find it helps in composing an image by removing the jumpiness you get viewing through a long lens.

The Canon lens has a separate switch for what the company calls Type 2 stabilization, which reduces blur in one axis only. This lets you take a smooth panning shot with the camera held horizontally. (Actually, it works with the camera held vertically, too, but most people pan with the camera in a horizontal position.)

The Nikkor has no such switch, but it does the same trick, as the motion sensors detect rapid linear movement and automatically switch the lens to single-axis VR. You can turn this off by switching the lens to Active mode. This allows you to shoot, say, from a moving vehicle, or follow a subject with continuous autofocus, without the camera interpreting the movement as panning.

We tested both lenses' image stabilization by shooting a dot-pattern target, then analyzing the images using DxO Analyzer 2.0 software. We had four shooters (ranging from pretty shaky to fairly steady) take the shots, starting at the reciprocal shutter speed (i.e., 1/200 sec for an effective 200mm focal length) and progressing to slower shutter speeds, with and without stabilization engaged.

The software then gave us the Blur Factor numbers at each shutter speed. (A Blur Factor of 1.0 is fairly sharp, while a Blur Factor of 8.0 is awfully blurry.) By comparing the numbers with and without stabilization, we determine how much handholdability is gained. For example, if a test shooter averages a Blur Factor of 2.0 at 1/200 sec without stabilization and gets a similar Blur Factor at 1/25 sec with stabilization, that's a gain of 3 full stops -- from 1/200 to 1/100, 1/50, 1/25. (Technically we should call these "EV steps," but everyone says "stops," so that's the term we use.)

We've found that image stabilization provides more benefit (measured in stops) to shaky people, and less to those who start out steady. It seems a paradox, but if you think about it, it makes sense. Consider the wiggly handholder who needs at least 1/250 sec for a sharp shot with a given lens. Image stabilization will likely allow this person to shoot at 1/30 sec -- a 3-stop gain. Now consider the steady shooter who can handhold the same lens for a sharp shot at 1/60 sec. Switch on image stabilization, and this shooter might be able to drop the speed to 1/15 sec. Sure, he's now shooting at a slower shutter speed than Mr. Shaky, but he's gained only 2 stops.

Canon says the extra stabilizing mojo of its lens comes from a new IS unit with reduced friction in the moving elements, along with a new stabilizing algorithm developed specifically for the lens. Nikon says its updated VR II has "greatly expanded" the detection of low-frequency vibration. Whatever the reasons, this latest generation of anti-shake lenses work very well. In our tests, the Canon consistently delivered up to 3.5 stops' gain at 200mm. The Nikon at 200mm averaged a gain of up to 3 stops, and at 300mm did even better -- up to slightly over 4 stops' gain.

The bottom line: Image stabilization has been a proven technology for more than a decade, and these two lenses show that it's never been better. If you like to shoot handheld in available light, stabilized lenses are well worth the extra cost.

The images below were taken handheld with the Canon lens at 200mm, shots without stabilization are getting soft at 1/160 sec and are unusable by 1/40 sec. With stabilization,shots are still sharp at 1/20 sec.

Magnification counts:
The greater the magnification (relative image size on the film or sensor), the greater the effects of shake. If you stay in the same place, but zoom to a longer focal length, shake gets magnified, too. Keeping to the same focal length but getting closer to your subject also increases magnification. (Handheld macro shots get especially jumpy; we describe the phenomenon in our test of the 105mm f/2.8 Micro-Nikkor VR, September 2006).

You can't stabilize kids:
Image stabilization counteracts movement of the camera, not the subject. If you're photographing a bouncing brat or bumptious bowwow at 1/15 sec, no amount of image stabilization will unblur the image. Use flash. Sorry.

Don't drift away:
Concentrate on one detail in the image, and stay there. If the image starts to drift in one direction, don't try to counteract the drift! You'll end up doing a wagging motion as you shift the camera...and the image shifts the other way...and you reshift the camera...and the image shifts the other way... Your arms tend to aim where your eye is looking, so concentrate on following one single point with your eye, not your hands.

It craves power:
Stabilization uses more battery power. Neither Canon nor Nikon have hard figures on added usage because everyone's shooting habits differ. Canon gave us a rough estimate of 10 percent extra power usage if a shooter engages IS for a second before each shot. That's not much, but be aware of it.

Tripod concerns:
Both Canon and Nikon produce some lenses that can detect tripod use, and stabilize for mirror slap accordingly. Neither of the lenses tested here do that, however, so turn off IS or VR when you use these optics on a tripod. Check the manufacturer's recommendations for other lenses.

Image Stabilization: What is, & what isn't

Another type of image stabilization specifically exploits digital capture. Pioneered by the now-defunct Minolta, this technology moves the camera's CCD imager to compensate for motion, somewhat like an outfielder jockeying under a tricky fly ball. Its supreme advantage: It usually works with any lens that can be fitted to the camera. A mild disadvantage is that you can't see the effects of the stabilization, because the sensor in an SLR is live only at the time of exposure. (Yes, Panasonic and some Olympus DSLRs have live preview, but they don't use sensor-based stabilization.) Currently Pentax (Shake Reduction) and Sony (Super SteadyShot) equip digital SLR models with sensor-based stabilization. We have found that these systems, like their lens-based counterparts, can provide up to 2 to 3 stops' advantage in handholding.

The situation in compact cameras is more confusing. A number of them have true optical image stabilization, of either the lens-based or sensor-based variety. (A compact with sensor-based stabilization can actually show the effect on its LCD, as the sensor remains live for viewing.) These can work exceptionally well, since compacts have no inherent vibration. But if you hold these cameras with your arms out, it's harder to keep them steady.

Then there's "digital" stabilization, which in many cases does nothing to actually sharpen the image. Most of these features simply boost the ISO up to 1600 or 3200 to allow for faster shutter speeds, and they add extra noise reduction, which can lower the resolution, too. A few compacts have electronic stabilization similar to that used in video cameras, sampling the pixels around edges and manipulating them to form a crisper image. An advantage: It can sharpen a moving subject, which optical stabilization can't do. But the improvement is limited, and the resolution of the image can suffer.

Our recommendation:
Optical image stabilization is the real deal, but if you want it in a compact camera, check the fine print in the specs carefully.

The reciprocal rule

The rule:
To ensure decent sharpness in handheld shots, use a shutter speed equal or faster to the reciprocal of the lens' focal length.

Translation:
With a 200mm lens, use a shutter speed of 1/200 sec or faster; with a 400mm lens, 1/400 sec; and so on.

The fine print:
This is about as loose a guideline as you can get. If you shoot at closer than "normal" distances, you'll need faster shutter speeds. Ditto if you're shooting with very long teles. On the other hand, if you're shooting at long distances, and can brace the lens and/or your elbows on something, you can get away with slower speeds.

Digital advisory:
That 1.5X or 1.6X lens factor you get with most consumer DSLRs counts. If you're using a 200mm lens on a camera with a 1.6X lens factor, your equivalent focal length is 320mm. So your safe shutter speed without stabilization is, yes, 1/320 sec.

Canon-70-200mm-f4L-EF-IS-USM-AF-Canon-5D-with-Can

Canon-70-200mm-f4L-EF-IS-USM-AF-Canon-5D-with-Can

Canon 70-200mm f4L EF IS USM AFCanon 5D with Canon 70-200 f/4L IS. 1/3200 at f/4 ISO 320. This lens is sharp, fast-focusing, and feels great in the hand. I had no trouble tracking herring gulls on the ground and in the air with this lens.Photo By Jack Howard
Canon-70-200mm-f4L-EF-IS-USM-AF-Canon-5D-with-Can

Canon-70-200mm-f4L-EF-IS-USM-AF-Canon-5D-with-Can

Canon 70-200mm f4L EF IS USM AFCanon 5D with Canon 70-200 f/4L IS. A telephoto lens is great for getting details of things that aren't possible to approach physically, such as the top of this stadium, which is promoting some sort of sporting contest.Photo By Jack Howard
Canon-70-200mm-f4L-EF-IS-USM-AF-Canon-5D-with-Can

Canon-70-200mm-f4L-EF-IS-USM-AF-Canon-5D-with-Can

Canon 70-200mm f4L EF IS USM AFCanon 5D with Canon 70-200 f/4L IS 1/2000 at f/4 ISO 320. Focused to about 10 feet, wide open, the Canon 70-200 f/4L IS provides a nice, sharply defined plane of critical focus to draw the viewer's eye towards the subject.
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