Whenever I see anything on the image stabilization not working, I'm always wondering how a person came to that conclusion ... because I've noticed a lot of mis-conceptions about what image stabilization is, what it's supposed to do, and how it works.
It's entirely possible that the IS feature of your lens has failed, but... just to make sure this isn't a mis-understanding...
When you take a photo and it's a hand-held shot, there's a possibility that the shot will end up with blur caused by camera movement because the camera was not steady enough given the shutter speed being used at the time.
If your SUBJECT is moving, then IS wont do a thing for you... it only helps protect against blur caused by CAMERA movement... not SUBJECT movement. I've used caps for emphasis on those points.
The speed necessary for this is typically arrived at by taking the focal length of the lens (e.g. let's say it's 200mm) and multiplying it by the crop-factor of the camera body (which for your 7D and 600D is 1.6) and use that (or rather the inverse of it) as your shutter speed. For 200mm it would be 200 X 1.6 = 320 or 1/320th (or faster). This would be the minimum speed you can use for a hand-held shot ASSUMING the photographer knows how to use correct body posutre for a stead hand-held shot and is actually trying their best to be steady. That means the camera is right up to your face (yes... with your nose smudging the display) and your arms and elbows tucked in below the camera to support it from below while your elbows are resting against your belly to "brace" the camera and your weight is completely centered over your legs and your legs are spread slightly into a bit of a boxing stance. Again, that's just for "camera" movement being the cause of blur. If you're photographing a fast moving subject and trying to freeze the action then that speed still wont be fast enough -- but that's a different discussion.
Any body movement on your part needs to be MINOR. It will never save you if the movement is large. Keep in mind it has elements inside the lens that it can shift to compensate for movement. But it can only shift so far before it hits it's limit of travel and has to reset the elements.
When you flick on the IS switch, the camera will attempt to sense motion and compensate. "Attempt" is the operative word here... its not a guarantee of success, it simply tilts the odds substantially into your favor.
An IS system is typically extremely successful at stabilizing your shot to 1 full stop below the normal minimum shutter speed needed when not using IS. That would be using 1/160th instead of 1/320th.
An IS system is typically mostly successful at stabilizaing for 2 full stops slower. That would be 1/80th.
An IS system is usually somewhat helpful even at 3 stops slower. That would be 1/40th.
An IS system is sometimes able save you at 4 stops slower depending on the lens and IF you get lucky. that would be 1/20th. (but using it at 4 stops slower is pushing your luck... don't count on these.)
Notice that with each full stop slower, your odds of success reduce. The IS system isn't a guarantee... it just tilts the odds in your favor (and if it's just a stop or two slow then it's HEAVILY tilting odds in your favor. But at 3 or 4 stops it's only SLIGHTLY tilting the odds in your favor.)
Beyond 4 stops... "fuhgettaboutit"... it's not happening. IS isn't going to save you. It's not even going to be a little bit helpful. Bet on that shot not coming out.
If you absoultely need a solid shot, use a tripod. If you can't use a tripod, use a monopod or the string trick. I sometimes look for something to brace myself... a wall or column to lean on, a railing to rest the camera on, etc.
If your'e sure your tests are valid, you're using proper technique and working within the limits of what IS is supposed to be able to do as compared to what would be needed without using IS, then it's possible the lens is defective. Dirty contacts may indeed be the problem, but there are other possibilities. Canon warns that the gold plating on the metal contacts is thin and that a pencil eraser can take off the plating. Use a clean, but soft cloth to clean the contacts (nothing abrassive.)
Tim Campbell
5D III, 5D IV, 60Da
