|
Go steady Almost everybody who has watched footage shot on a handheld camcorder understands the term “image shake”. No matter how hard the camera person tries, the subject of the image jumps about. Using the camera's zoom makes
matters even worse, as the lens magnifies any tiny vibrations. Canon has tackled the problem by developing innovative Image Stabilization (IS) technology. Shake it up Hands typically shake at between one and five tiny movements per second, and the camcorder in their grasp shakes with them. This has the effect of moving the subject off the lens’s optical axis, resulting in the appearance
of a jumpy subject. The magnification of the lens exaggerates this effect. Tripods can help combat the problem, but their use is not always practical or desirable. Different cameras, different approaches Canon has developed three effective IS solutions which are used variously throughout the camcorder and pro-photo lens range. The first of these is Electronic IS (found in camcorders such as the MVX25i). The other two systems are known as Optical IS (OIS) because they use special corrective elements inside the lens itself to correct movement before it hits the sensor. The two OIS methods are Tilt System OIS (found in
camcorders such as the MVX3i) and Vari-angle Prism OIS (VAP) (found in camcorders such as the XL1-S). Unlike many lesser model camcorders which use algorithms to detect movement in the recorded image, Canon's IS systems all utilise sensors to detect movement. This is not only a more effective approach to IS, it also gives
Canon camcorders the very important advantage of being able to stabilise an image during zooming and panning. Electronic IS reads extra pixels from outside the border of the image being captured during shooting. When the motion sensor detects unwanted movement off the optical axis, a special algorithm 'shifts' the image and any
extra pixels required back into position, essentially 'removing' the unwanted vibrations. VAP and Tilt System IS are both known as Optical IS (OIS) systems because they both use corrective lens elements to 'remove' vibrations and movement before the image is recorded. In both VAP and Tilt systems, a special corrective OIS lens group is designed to refract or ‘bend’ light rays. The VAP system uses a liquid filled bellows which changes shape to alter the degree of correction. The Tilt
System shifts a moveable correction element perpendicular to the optical axis to achieve the same result. When the camcorder is moved off its optical axis by vibrations, a detection system consisting of two tiny gyros leaps to action. Highly
responsive coils either change the shape of the bellows (VAP) or move the IS lens group (Tilt System) by precisely the right distance in the direction of the vibration. Design of the corrective optical systems allows correction of vibrations in both
horizontal and vertical directions. Hair trigger response All of this starts to happen within approximately 0.002 of a second of a vibration being detected. This essentially immediate response allows the OIS system to move the correction lens group with the vibration, effectively
cancelling image shake effect. back
|
