500F4IS: IS Mode 2 doesn't turn off if on tripod
Hi,
it is my understanding that later generation IS systems on modern lenses like the Canon 500F4IS are expected to turn themselves off in Mode 2 if they are mounted on a tripod. For that reason I leave the IS mode set to 2 regardless if I use a tripod or not.
Now, there is no doubt that upon half-pressing the shutter button on my 500F4IS the IS motors activate (I can hear them) and the image in the viewfinder stabilizes even if the lens is mounted on the tripod and in mode 2. I've always wondered about the apparent contradiction to what's stated in the lens manual and the recommendations here and on other gear forums but didn't think too much of it.
But today, I tried shooting at very low shutter speed and decided to see if I can get better sharpness using a remote shutter release. The 500F4IS was in mode 2, mounted on a Gitzo, the Mongoose was locked down, no wind, single focus shot, central focus point, I was not touching the lens or camera and upon half-pressing the remote shutter release the IS activated. Not only that but the image in the viewfinder moved considerably (usually to the left) and then slowly reapproached the original position. Total time it took to restabilize was 1 - 2 sec. Frankly, I was and am stunned.
For a given focus target, the IS creep and back was very reproducible. On a slightly different target it tended to reproducibly go left down (think 7 o'clock) and went back up.
What can cause this? Has anyone else experienced this? And how did you resolve it?
Thanks in advance. JR