I've been using the kit 17-85mm IS lens on the Canon 20D, and have just got a 70-300 IS DO lens. The IS is very easy to "feel" on the 70-300, as a sort of noise/ vibration as it works, especially at 300mm. I don't get any feel from the 17-85 at all from the IS, and I must admit I've found it very hard to see from the images whether it's working or not, whereas on the 70-300, turning on the IS makes a night and day difference.

Any thoughts on whether my 17-85 is functioning correctly??

Graeme

The benefits of image stabilization are most obvious with long lenses (higher magnification) and/or longer hand-held exposures.  But in either case, you should be able to see through the viewfinder that the image is steadier using IS than not.

You can test your 17-85 by taking a series of long (1/15th, 1/8th or slower) hand-held shots at the 85mm end with and without IS.  The difference should be readily seen.  

Of course, if you are one of those individuals blessed with very steady hands, all bets are off  :D

Paul

Well, it seems that the stabilizer on the 17-85 is working, but that it's much harder to "see", and you can't "feel" it as easy as on the 70-300 where the difference is very visible. I guess that as the length of the lens changes, the motor needs to work harder and you can feel it more easily. Thanks,

Graeme

The reason it's not as visible on the 17-85 is that the "impact per time" is much less. Your visual perception doesn't change its frame-rate/shutter-speed when you change the focal length of the lenses and as such, wider angles are much less shaky in your eyes. I bet that if you compare the 17-85 at the long end and the 70-300 at the short end, the visual efficiency of the IS (in the viewfinder) will be similar.

All very interesting. How slow can you shoot with a 17mm and IS?

Peter