Some of Canon’s competitors have chosen to use in-body image stabilization. The technique
involves moving the image sensor in a controlled fashion, based on signals from
movement detecting sensors in the camera body. The obvious advantage of this system
is that users have some sort of stabilization available with almost any lens they connect
to the body. Short focal length lenses require smaller sensor deflections; 24 or 28 mm
lenses might need only 1 mm or so. Longer lenses necessitate much greater movement;
300 mm lenses would have to move the sensor about 5.5 mm (nearly 1/4”) to achieve
the correction Canon gets with its IS system at the same focal length. This degree of
sensor movement is beyond the range of current technology. Short and “normal” focal
length lenses need stabilization much less often than long lenses, so the lenses that
need the most help get the least. Further, in cameras with smaller than full-frame, 35
mm film size sensors, equivalent focal lengths become longer, by a factor of 1.5 or 1.6,
exacerbating the problem by making all lenses longer.
Less significant but still worth mentioning is the fact that in-body stabilization is not visible
through the finder, whereas Canon lens-based stabilzation definitely is. Also, while
in-body stabilization works for many lenses, it does not presently work for all; high magnifications
and macro lenses have caused it difficulties.
In the Canon IS system, the Image Stabilizer has an actual
lens group that can be moved up and down, or side-toside,
in parallel to the imaging sensor or film plane. A pair
of sensors in the lens can detect horizontal or vertical
shake. Signals from these sensors are sent instantly to a
microprocessor in the lens and analyzed. The microprocessor
then causes a group of lens elements, held in
place by a device called a coil, to move at the same amplitude
and frequency of the shake to cancel it effectively.
Canon is able to generate excellent image quality by stabilizing the image optically
before it ever reaches the imaging sensor in a digital SLR.
With the optical IS used by Canon, each lens with IS has a stabilizer unit designed for
that lens's needs. The unit in a lens such as the EF 28-135 f/3.5-5.6 IS USM or the EF-S
17-85 f/4-5.6 IS USM is vastly different from the powerful, broad movement stabilizers
in lenses such as the EF 400mm f/2.8L IS USM or the EF 600mm f/4L IS USM. All over
the world, photographers depend on Canon IS to help them achieve the highest possible
At some point, in-body stabilization may improve to the point at which such technology
may be appropriate for certain segments of Canon’s DSLR range. It would be senseless
to rule out such a possibility. Even now, differences in unit cost are not enough to be
significant factors in such a decision. The bottom line is performance.