Lens technologies: Image Stabilisation (IS)
One of the major causes of poor image quality is camera shake. If you move the camera during the exposure, the image is likely to be blurred. Canon has a solution by way of a specially designed group of lens elements to help overcome this problem – an optical Image Stabilizer.
How it works
Canon's Image Stabilisation (IS) is controlled by a group of elements inside the lens which moves at right-angles to the lens axis. The movement of this special lens group is controlled by an on-board microcomputer and it works by counteracting the shaking of the camera.
When IS is switched on and the shutter button is partially depressed, the stabiliser lens group, which is locked in a central position when not active, is released. Then two gyro sensors start up and detect the speed and angle of any camera movement. The detection data is passed to a microcomputer which analyses it and prepares an instruction for the special stabiliser lens group. This instruction is transmitted to the stabiliser lens group which moves at an appropriate speed and angle to counteract the camera movement.
This complete sequence is repeated continuously so that there is an instant reaction to any change in the amount or direction of the camera shake. It takes about one second from the moment you partially depress the shutter button for the stabilisation to become really effective. The stabilisation action continues for about a second after you take your finger off the shutter release.
Above Exploded view of the IS mechanism used in the EF 70-200mm f4.5-5.6L IS USM lens.
Benefits of IS
The original lenses that featured this system gave a correction ability of about 2 stops, allowing the lens to be hand-held two stops lower than is normally possible – 1/60 second gives similar results, in terms of sharpness, to shooting at 1/250 second, for example.
More recent IS lenses allow more correction, and we now see lenses that offer 3 or 4 stops correction. The EF 200mm f2L IS USM tops the list with 5 stops correction.
Low light photography
Image stabilisation offers real benefits when shooting low light and interior images, allowing you to shoot without the need of a tripod in increasingly challenging lighting conditions.
Lenses with focal lengths from 200mm to 300mm would be virtually impossible to use in low light when shooting handheld if they did not have image stabilisation. It allows the use of slow shutter speeds of 1/60 second and 1/30 second (depending on your camera handling), which you are likely to get in low light levels.
To take advantage of image stabilised lenses you need to take control of the shutter speed. Working in shutter-priority (Tv) mode is recommended as it means you can set the speed to what you know to be safe for hand-holding, and the ISO can be set accordingly.
One situation where the IS system can work against you is when you’re trying to follow the motion of your subject by panning. This is a technique often used to get a sharp subject against a motion blurred background. A problem arises when the camera cannot distinguish between your deliberate panning motion and unintentional camera shake.
The IS system detects the panning motion and seeks to counteract it. When it runs out of adjustment range, it resets and begins the next correction cycle. This behaviour can cause unpredictable results in stills photography and jerky movements when shooting movies. To address this problem some IS lenses have an additional ‘mode’ switch, which has up to three settings:
Mode 1 is the standard two axis operation (pitch and yaw) in which the camera attempts to correct any movement it detects. This is the standard mode intended for stationary subjects.
Mode 2 is intended especially for panning. It is designed to ignore motion in the direction of the panning, but to correct any detected motion at right angles to the panning direction.
Mode 3 is for photographers who don’t want the viewfinder image to be affected by IS. In this mode, stabilisation is applied only during the actual exposure.
Some recent IS lenses dispense with a mode switch altogether and instead incorporate automatic panning detection.
The reciprocal rule is a guide to the slowest shutter speed you should use when hand-holding your camera. This rule-of-thumb says that the shutter speed should be no slower than one over the focal length of your lens. For example, if your lens has a focal length of 400mm, your slowest shutter speed should be 1/400 second if you want to avoid blur caused by camera shake.
If you hold your camera correctly and you have a steady hand, you might get away with a shutter speed of 1/200 or even 1/100 second, but with image stabilisation you can easily take acceptably sharp images at much slower shutter speeds. With the EF 100-400mm f4.5-5.6L IS USM lens the image stabilisation enabled us to work right down to 1/13 second.
Far left: 1/13th second, shot at 400mm, no IS
Left: 1/13th second, shot at 400mm, IS enabled
Both shot with EOS 6D, EF 100-400mm f4.5-5.6L IS USM lens.
HISTORY OF IS
First lens with Image Stabilisation
In September 1995 Canon introduced the world's first lens featuring Image Stabilisation technology – the EF 75-300mm f4-5.6 IS USM – which provided a benefit of 2 stops.
Since then there have been over 30 zoom lenses, 15 prime (fixed focal length) lenses and a couple of macro lenses with built-in IS.
Best performing IS lens
The EF 200mm f2L IS USM boasts a full 5 stops correction.
Employing a newly developed algorithm, Hybrid IS optimally adjusts for camera shake based on information gathered by two sensors located in the lens. By precisely driving the optical correction system, the technology simultaneously corrects for angle and shift camera shake. Introduced in October 2009 with the EF 100mm f2.8L Macro IS USM lens.
Lens vs. camera
Canon’s original decision to house the IS system entirely within the lens has enabled it to optimise the operation for each lens. Improvements in lens and transducer design, together with increased processor power has made the IS system faster and more accurate.
Although further improvements in IS technology will be made it’s unlikely we’ll see much more than the current maximum of five stops. This is primarily because this degree of stabilisation is sufficient for most low-light shooting situations in which a photographer has to hand-hold the camera. Improvements in sensor design and reduction in sensor noise have made the option of increasing the ISO setting to achieve a faster shutter speed a more practical solution.
IS and video
To tackle the problems with camera shake encountered when shooting video with your EOS camera, Canon has recently introduced in-camera stabilisation. The EOS M5, announced in 2016, features 5-axis in-camera stabilisation, which digitally counteracts camera movement along five axes – horizontal, vertical, roll, yaw and pitch. It allows steady movie footage to be captured, even when using lenses without an optical Image Stabilizer.
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