john_blain

<p>Daniel,<br>

It is good to hear that I wasn't alone with this problem. I took the lens and camera to my Canon service centre 3 times and I think they have finally fixed it by reloading the firmware onto the lens. They say they have sent the original firmware to Canon HQ so you might get a better response.<br>

After my post on Oct 29th, I did some more tests and found that it was any F stop greater than F4 that caused the problem. I demonstrated it to them by doing the following:<br>

1. Set camera to Manual, F8 and 1/10sec with max zoom and IS on.<br /> 2. Take a picture normally<br /> 3. Take another picture by focusing then pressing the depth of field preview button to close the aperture then take the picture with DOF button pressed.<br /> 4. Compare the 2 pictures for image blur.<br>

I was finding that the first image was blurred (movement not a focus error) and the second was totally clear. This suggests that the closing of the aperture at the time the picture was taken was interfering with the IS. Closing the aperture before the picture is taken (with DOF button) does not produce the problem. Canon's method of testing IS in the lab would never find this because all they do is shine a light through the lens at F4.<br>

Good luck<br /><br />John</p>

<p>I bought this lens a month a go with a 5D body. The optics are fine but I think there is a serious problem with the image stabilizer when the aperture isn't fully open.<br>

I set the camera to 1/10 sec at F8 and put the lens at max zoom. I then took a photo of a static subject with and without IS switched on. The image with IS switched OFF was much clearer. If the aperture is set wide open at F4, this image blur does not occur with IS ON. It appears that the action of the diaphragm closing when the picture is taken is interfering with the IS. If you focus, then press the DOF button to close the aperture, then take the picture, the image is clear with IS ON.<br>

I sent the lens to Canon for investigation and they returned it saying no fault found. This is very disappointing since I have other cheaper lens that do not have this problem under these conditions.<br>

I would be interested to know if others have observed this.</p>