Canon 300mm F4 Image Stabiliser

I have had a Canon 300mm IS lens for about five years. My most often lens combination is the 300mm with a canon 1.4 TC (mark 2). I have noticed that sometimes when I engage the autofocus with the image stabiliser on it vibrates the lens inside for a second or so and then the image settles down. This means that sometimes I miss the shot if I am using the IS. I can't remember whether it has always done this or only recently. Is this normal for an image stabilised lens or do I need to send mine for a service / repair. Its had a lot of use as it is my primary lens. Thanks Mat:S3:

Mat,

It does take a moment (second or two) for the IS to engage and settle down, so that part is normal. I often hear a clunk when first starting, and the motor is revving up. Perhaps your IS motor is getting old? There are rumours that the 300 f/4 IS will soon be replaced, but that rumour has been around for over a year now. It would be nice to have a newer IS (the f/4 is version 1 IS) and better optics.

Roger

Hi Mat
I have owned two of those lenses, and the first one I owned was bought used. I had to replace the IS unit on it as it gave up working, but in its defence, it had done lots and lots of work. When it failed though it caused the image to jump inside the viewfinder. I have a feeling that the older, first version IS in some of the Canon lenses can give out after lots of heavy use.
Maybe best to get it checked out. Here in South Africa replacing the IS was pretty expensive...
cheers
Grant