I have a Canon T1i, and was recently shooting with my Canon 70-200/4 IS lens with IS "on". I've done this many times with no concerns. Works great. But this time I slipped on a Kenko 1.4TC (the one recommended for this lens). When I switched on the IS, I was hearing a regularly pulsating IS kicking in at 2 or 3 second intervals; whether I was shooting, or hold the camera still. I'm assuming the IS was working. But when no motion was caused to the camera? My images were steady, but is this Imaging Stabilizing working at prescribed intervals, a normal thing?It was making me nervous, so I turned the IS off except for only when I was about to take an actual shot. Usually, I would just leave the IS setting to "on" and shoot for longer periods of time that way.

Actually I am surprised that you hear the IS. Have you heard it without the converter? On both my 18-55 and 55-250 lenses I have never heard any IS noise that I can tell. Sure hear the AF motor. Hopefully my IS is working OK on both those lenses. Would be interested if others hear the IS when it kicks in. Hand held shots seem very sharp.Steve W.

I was under the assumption that lens IS was activated only when it felt necessary to stabilize. But when I attached the TC to the lens, I could hear it trying to stabilize at even intervals of 2 or 3 seconds..........even when held perfectly still. Again I ask, is this normal? Thanks

Yes, I hear it. It's just a very faint "zzzt" sound. I wouldn't consider it annoying at all. Actually, without actually trying it right now, it may be more of a "feeling" than a sound. But in any event, I am aware of it working. And....it does do the job. So the sound does not seem to be indicating any malfunction. At least I didn't think it was...unless you folks indicate differently.

The normal activation is when you press the shutter, AF being assisted as it were by the IS. What kind of TC is it? I have used Kenko Pro series and have not experienced this on either my 40D or 1DsMkII. I will have to try it on my T2i.I think I read that in video modes, the IS is run continuously .Dan -- 'A bad idea in search of a good cause is.. just a bad idea' ... me

BobTwrote:I was under the assumption that lens IS was activated only when it felt necessary to stabilize. But when I attached the TC to the lens, I could hear it trying to stabilize at even intervals of 2 or 3 seconds..........even when held perfectly still. Again I ask, is this normal? ThanksI have the same combination (T1I, 70-200 f/4 IS, Kenko 300 Pro TC) but haven't noticed the behavior you describe.Dave -- http://www.pbase.com/dsjtecserv

The TC that I have is : Kenko Teleplus C-AF 1.4X PRO 300 DGX.I just got it out again to double check, and the same things occured. Even when put down, that "zzt"(or what I considered to be the sound when the IS is being adjusted)occurs at about 2 second intervals even when the camera is motionless and lens cap is on. Makes no difference what settings I might switch to on the 70-200 lens. The only way to silence it is to turn the IS off. Might there be a camera setting causing this?It is loud enough to hear accross the quiet living room; as my wife hears it, too.The camera/lens does Image Stabilize, as it should. So it is functioning. But why this intervalic IS "searching" sound?I'm baffled. No way to return anything; as camera, lens, and TC are all well past their return periods(by quite a bit). It's my own fault that I didn't try the TC when I got it (3 months ago)until yesterday.