Camera shake (unintentional movement of a camera during an exposure) is probably the most common cause of pictures being spoilt by a lack of sharpness. Nikon's Vibration Reduction (VR) system helps to reduce the effects of camera shake.
It is important to draw the distinction between subject movement and camera movement (camera shake). The speed of the former will dictate the shutter speed required to arrest that motion and render the subject sharply; VR has no effect on subject movement. However, if the camera moves in relation to the subject during the exposure, regardless of whether the subject is moving or not, there is a risk that some or all of the image may be blurred. It is in these circumstances that VR can be of benefit.
In the case of the panning technique, which involves swinging the camera deliberately to track a moving subject, VR can help by reducing the effect of camera movement in the plane perpendicular to the path of the camera's motion. All Nikon VR lenses are capable of detecting a panning motion and only dampening camera movement in the opposite plane.
The VR Nikkor lens contains a group of elements that have two motion sensors attached to them. Nikon refer to these as 'angular velocity sensors'; one detects "yawing" motion (rotation around a vertical axis), and the other detects "pitching" (rotation around a horizontal axis).
When the VR system is active these sensors detect information concerning lens movement continuously. Using the information calculations are performed instantaneously and based on the results of these the VR lens group is moved by a group of motors, known as Voice-coil motors (VCM), to an appropriate position that counters the effect of any unintentional lens motion.
The VR system continues to monitor lens motion and will adjust the position of the VR lens element group accordingly as soon as it detects any changes in the orientation of the lens. The micro-computer used to process the information from the motion sensors, perform the calculations, and send instructions to the VCMs operates in a faction of a second; typically taking no more than 1ms (1/1000th second) to complete its functions.
Furthermore the VR system is capable of determining whether or not the motion of the lens is likely to be intentional, such as the technique of panning; in this situation only motion in the plane perpendicular to the movement of the lens is corrected. This is achieved by the use of complex algorithms contained in the firmware of the VR lens. These algorithms are based on a large sample of information collected from a wide variety of conditions that induce unintentional camera vibration; the microcomputer uses them to control the poisoning of the VR lens group.
Nikon claim that their VR system is capable of reducing camera shake to a level where it offers the equivalent of shooting with a shutter speed three stops (8x faster) faster - but what exactly does this mean in practice?
Well it is not the same as saying that VR eliminates all risk of camera shake or vibration from ruining a shot! What Nikon is saying is if there is a 25% risk of camera shake occurring at 1/125 second with a particular focal length lens, then on average, with the VR activated the risk remains the same if that lens is used at 1/15 second.
Nor does it mean if you apply the often-quoted rule of thumb that states the slowest shutter speed for any particular focal length for hand-held shooting should be its reciprocal that VR will be effective at a shutter speed three stops slower. For example, using a focal length of 400mm, the rule of thumb suggests a minimum shutter speed of 1/400 second would be required to achieve a sharp image with a hand-held lens, but there is absolutely no guarantee that with VR active shooting at 1/50 second (equivalent to three stops slower) will produce usable results.
Many factors affect the ability of photographers to hand hold a camera and achieve acceptably sharp images including their physiological condition (e.g. respiration rate due to their level of exertion), shooting conditions (e.g. atmospheric influences such as high winds) and the actual length of the exposure. Therefore, use of VR should be considered on a circumstance-by-circumstance basis.
If you want to use a VR lens it is imperative you consider the model of camera you will use as well, since only certain Nikon cameras support the VR system. Currently, the Nikon F6, F5, F100, F80, F75, F65, D2-series, D1-series, D100, D70, and D50 are the only Nikon camera models that are compatible with the VR feature; VR lenses can be used on other Nikon cameras but VR will not function.
To put Nikon's VR system into perspective it is an extremely useful feature that helps to achieve sharp pictures in those situations when there is no alternative to shooting with a camera supported by hand but it is no substitute for a solid camera support such as a tripod, and a well-disciplined camera technique.
© Simon Stafford
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