Information posted by Chuck Westfall of Canon USA:
The instruction sheets with my IS lenses say to turn the IS function OFF
when using a tripod. I have heard other photographers argue the
opposite.
Would you discuss the pros/cons of this?
The answer depends on which type of IS lens you're talking about. With
the IS super-telephotos (300/2.8L IS, 400/2.8L IS, 500/4L IS and
600/4L IS), it's OK to leave IS turned on when the lens is mounted on
a tripod. For all other current IS lenses (28-135/3.5-5.6 IS,
75-300/4-5.6 IS, 100-400/4.5-5.6L IS, and 300/4L IS), it is much
better to shut off the IS function when the lens is mounted on a
tripod.
Here's the explanation for the 28-135 IS, 75-300 IS, 100-400L IS, and
300/4L IS lenses:
The instruction manual warns that the IS stays on after pressing the
shutter button half way, and that use of IS on a tripod may damage the
lens.
Here's what the instruction book says (page E-8): "Do not set the
image stabilizer switch to 'I' when using the camera on a
tripod. Doing so may cause the image stabilizer to act
erratically. Turn the image stabilizer off '0' before using the camera
on a tripod."
There is no language here or anywhere else in the instructions
concerning damage to the 28-135 IS caused by using the camera on a
tripod. All they're saying is that using IS while the camera is on a
tripod "may cause the image stabilizer to act erratically."
Why does tripod use cause a problem?
Short explanation: The IS mechanism operates by correcting shake. When
there is no shake, or when the level of shake is below the threshold
of the system's detection capability, use of the IS feature may
actually *add* unwanted blur to the photograph, therefore you should
shut it off in this situation.
Longer explanation: Remember that the IS lens group is normally locked
into place. When the IS function is active, the IS lens group is
unlocked so it can be moved by the electromagnetic coil surrounding
the elements. When there's not enough motion for the IS system to
detect, the result can sometimes be a sort of electronic "feedback
loop," somewhat analogous to the ringing noise of an audio feedback
loop we're all familiar with. As a result, the IS lens group might
move while the lens is on a tripod, unless the IS function is switched
off and the IS lens group is locked into place.
Is IS best kept off, then turned on for each shot as needed, then turned
off again, much as one would use the exposure compensation dial?
For most hand-held work, leave the switch on; for tripod work, shut it
off, as noted in the instruction book. The recommendations above do
*not* apply for the 300/2.8L IS, 400/2.8L IS, 500/4L IS, and 600/4L
IS. Here is some information for them:
with 300/2.8L IS, 400/2.8L IS, 500/4L IS and 600/4L IS] Does IS operate
when the lens is on a tripod or not??
I can positively confirm that it does, and quite well as a matter of proven fact.
The Owner's Manual (page 12) says it does not.
We know. But our testing indicates otherwise.
Canon Inc.'s EF Lens Tech Report (Vol. 13) implies that it disengages but
then says it stabilizes when using a tripod.
I see no such implication. My copy of this report says: "With previous
IS lenses, it was necessary to turn off the Image Stabilizer when
using a tripod because it might operate incorrectly. But the Image
Stabilizer installed on these IS lenses has an additional function
that prevents improper operation when using a tripod. It also corrects
camera vibration caused by slow shutter photography when using a
tripod: a common problem with Super Telephoto lenses. About one second
after the shutter is pressed halfway, the unit automatically
determines that a tripod is being used from the output of a vibration
gyro." These statements are 100% accurate based on my testing. There
are no other references to the use of IS on a tripod anywhere in this
report, as far as I can tell.
My own guess is this. When the tripod/head is rigid and there is
little or no vibration, IS does disengage. When you loosen the head --
as for following birds in flight -- the gyros sense some vibration and
the IS begins to operate again.
This is not quite right. Based on my own personal testing and
observation, as well as a personal consultation with one of Canon
Inc.'s chief executives in the Lens Division, these lenses effectively
have 2 IS modes *within Mode 1.* The decision on which mode will be
used is made by the equipment, not the photographer, based on an
evaluation of the degree of detected movement, as follows:
A. When the lens is mounted on a steady tripod and the shutter button
is pressed halfway, the IS begins to operate immediately and the image
in the viewfinder goes through a very slow vertical shift for about 1
second. After that, if the shutter button continues to be pressed
halfway, the IS mechanism automatically goes into a special mode which
is designed to detect and correct for mirror slap and shutter movement
at slow shutter speeds. Based on my personal testing, it does this job
spectacularly well. Close examination of results from shooting tests
definitively proves that there is no advantage to be gained by
shutting off IS, or even by locking the mirror prior to exposure.
B. When the lens is mounted on a monopod or hand-held *and* the gyro
sensors detect movement exceeding a certain rate, the IS mechanism
switches into its conventional correction mode which is designed to
compensate for relatively gross and/or erratic lens movement.
So, what you're seeing when you loosen the ball head and start moving
the lens is essentially an automatic switchover from "tripod IS" to
"conventional IS."
Best Regards,
Chuck Westfall
Assistant Director/Technical Information Dept.
Camera Division/Canon U.S.A., Inc.
