Keeping a Steady
Picture
In a way, it’s too bad that the full-size camcorder
went the way of the dodo as far as the consumer market is concerned. There was the
definite convenience of simply being able to take a tape made on one of these recorders
and to slam it into your VCR at home and have it work. The downside, of course, was that
the big units were heavy and tended to produce fatigue in very short order.
So today's tiny camcorders are a definite boon to those who
want to preserve their lives on video. But the bigger machines did have one big advantage
when it came to the simple business of shooting an image: their very heft made it much
easier to hold them steady. It’s always difficult to keep a camera from jiggling,
especially when the lens is in its telephoto mode, but sheer weight did help. Now that
most camcorders weigh ounces rather than pounds, many videos are more apt to promote
nausea than an understanding of some exotic clime.
There are things you can do to minimize the shakes, without
having to upgrade your equipment. One is simply to be sparing in the use of the longer
focal lengths of your zoom lens -- if you can get closer to your subject, you are more
likely to get a steadier image than if you shoot far away with the zoom cranked right out.
That’s not always possible, of course. Mounting the
camcorder on a solid platform is another answer. This might mean simply parking it on a
wall or tree stump, or it might involve the use of a tripod for long shots, especially if
they are of more than a few seconds duration.
Still, you may not want to carry that extra piece of gear
around all the time. Fortunately, built-in image stabilization featured on many camcorders
often makes that unnecessary.
Most systems use motion sensors to determine the direction
and extent of tiny camera movements -- the sort that happen when your hand shakes slightly
holding the camcorder. These are digitized and analyzed, and the data collected used to
activate the correction mechanism, whatever it might be.
Perhaps the most elegant, if rare, technique uses the
information from the sensors to make minute corrections optically, in effect continuously
re-aiming the lens system to compensate for the camera motion.
The heart of the system is a special complex prism whose
characteristics change as dictated by the sensors. As the camera moves about, servo motors
connected to the motion sensors create a sort of variable prism that essentially keeps the
camera’s image sensor focused on the same part of the scene in spite of the actual
position of the camera.
The system works best on broad movements; tiny, jerky moves
are dealt with less effectively, but some benefit is still achieved, especially with long
shots. The main annoyance of the system is that sometimes the image seems to keep moving
even when you stop the camera motion. If you are executing a smooth pan to the left or
right, the sensors settle down, only to reactivate themselves when you stop. They then try
to continue the pan for the moment, and you sometimes find yourself ending up aimed at the
wrong spot.
The main advantage of the optical system over purely
electronic equivalents, at least at first, was that it involved no degradation of picture
quality. That was in contrast to the first electronic stabilizers, which operated by using
only a portion of the camera’s image pickup device. In the stabilizer mode, the image
sent to tape was picked up from the central portion of the sensor, with a margin of unused
pixels around the periphery. As the camera moved, the desired portion of the image moved
around the image sensor, and the motion detectors "followed" the image,
automatically re-assigning the pixels to make the image seem still. As with the optical
system, the electronic stabilizers worked best with relatively slow movements, but they
were quite effective nonetheless.
Deciding how to reassign the pixels can be done a number of
ways. Some camcorders use motion sensors similar to the ones employed in the optical
systems, while the others continually analyze the signal itself to track where an image is
on the sensor at any moment and make the appropriate adjustment. The main drawback of the
early electronic systems was that some of them did entail a small compromise in picture
quality, but this slight sacrifice was deemed acceptable when weighed against the
advantages of the steadier picture, and the somewhat lower resolution is still apparent in
some less-expensive models. It wasn’t universally true even in the early days,
however, and now the differences have dropped to the vanishing point.
However the camcorder makers achieve it, it’s apparent
that image stabilization brings a real benefit to the making of home videos, and the
improving technology has got rid of most of the early bugs. The closing of the gap between
optical and electronic stabilization has mostly happened because of improvements in the
latter. But optical is undoubtedly more expensive, and the narrowing of the differences
between systems may not justify the optical alternative.
There will always be a place for physical aids to steadier
pictures, such as tripods or handy stone walls, but the high-tech solutions are a valuable
addition to camcorder technology, and are only likely to improve further as time passes.
They’re unlikely to go away, anyway.
...Ian G. Masters
ian@mastersonaudio.com
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