Tuesday, January 1, 2008
Gadget Bag: Image Stability
Get sharp handheld exposures with image-stabilization technologyThis Article Features Photo Zoom
Shooting at fully extended telephoto lengths without a tripod is a recipe for a blurry shot—unless you have image-stabilization technology. With image stabilization, you can get sharp handheld exposures at longer focal lengths and slower shutter speeds.
All true image-stabilization systems work in basically the same way. The system monitors camera movement and triggers a mechanism that shift key components to counteract the movement. In lens-based systems, with which we’re primarily concerned here, lens elements actually move in this process.
The other variation of image stabilization is built into the camera body. These systems work by shifting the image sensor, rather than lens elements, for essentially the same result. Companies like Olympus, Pentax and Sony feature models that utilize this technology, while Panasonic offers it both in lenses and
the camera body.
As the two biggest manufacturers of cameras and lenses today, both Canon and Nikon have a similar system for correcting camera shake, as do Panasonic, Sigma and Tamron. Although reluctant to discuss the innermost workings of their respective systems, each of these manufacturers is willing to reveal how its individual system works in general.
Nikon has Vibration Reduction (VR); Canon offers Image Stabilizer (IS); Panasonic features MEGA Optical Image Stabilization (MEGA O.I.S.); Tamron’s solution is called Vibration Compensation (VC); and Sigma has its Optical Stabilizer (OS) system.
Canon’s approach to its Image Stabilizer technology began in 1995 with the introduction of its first 75-300mm IS lens for SLRs. Since then. the goal has been to create a perfectly clear image when the shutter is snapped and a stable viewfinder image to make composition easier when taking a shot at slower shutter speeds.
The Canon Image Stabilizer system is composed of sensors, actuators (a device for controlling or moving a mechanism) and an optical-correction system. The system works with a set of two vibration gyros and a microcomputer to detect movement. Canon's IS system moves the IS lens to compensate for shake by shifting the position of the lens, creating a clear exposure. Note, also, that Canon IS has a Mode 1 and Mode 2. Mode 1 uses both the X and Y axes when the IS is on, but when Mode 2 is utilized (best for panning a continuously moving subject), the X axis isn’t compensated for.
The newest IS lens from Canon is its EF-S 18-55mm ƒ/3.5-5.6 IS standard zoom lens. This wide-angle lens lets you shoot handheld at up to four stops slower with IS enabled. Canon’s offering of IS lenses includes standard zooms, telephoto and super-telephoto zoom lenses.
Nikon’s VR lens system is controlled by two sensors that use the physics theory of angular momentum, which states an object rotating (the VR lens) will continue to rotate at the same point unless it’s acted upon by an external force—in this case, a Voice Coil Motor system that detects movements on the vertical and horizontal axes to compensate for shake. So every 1/1000th of a second, the angular velocity is examined, and the data is sent to a microcomputer in the lens that calculates the amount of compensation that’s needed.
To compensate for different shooting scenarios, Nikon has two modes for the new VR II lens system. The first is Normal Mode, in which only slow or wide camera movements are compensated for. The second, Active Mode, anticipates some camera movement, such as panning the camera, and corrects only for unwanted vertical movements.
The new Nikon AF-S Nikkor 400mm ƒ/2.8G ED VR telephoto lens incorporates this second generation
of Vibration Reduction technology, which lets you use up to four shutter speeds slower than you could normally shoot handheld. This new super-telephoto lens has a fixed maximum aperture of ƒ/2.8, allowing for a shallow depth of field.
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