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| © Greg Neumaier / Glasshouse Images |
| More than a decade in the works, Canon's
and Nikon's latest shot-steadying lenses
rely on motion sensors and shifting
elements within their barrels. Click photo to launch a gallery of images shot with these lenses. |
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.
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.
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