I rented a 100-400 from Adorama earlier today and forgot to ask which way to turn on the IS - Is it the 1 or the zero position? Adorama is closed now for Shavis. Thanks for any assistance.
The descriptions posted so far are getting closer to correct, but are not fully there. To further clairify, the "I" (which looks like a little like a "1" , and is printed like a "|"), is for IS on, and it is paired with the "O" for IS off.
The 1 and 2 switch is for pan mode, but does not relate directly to vertical or horizontal. The "1" position is normal IS mode, with normal Image Stabilization in both directions of movement, which are most often the two directions of up down and left right. The stabilization actually works with the lens pointing in any direction, including vertically straight up, in which case you would need to call the two directions of stabilizaton motion North-South and East-West, or something like that. The "2" postion is for pan shots, but it does not care about direction. What it does is sense panning, checking both directions of motion all the time. If one of the two directions senses panning that is at a high enough rate, it turns off the IS for that direction, and leaves stabilization on for the other direction. So it does not care if you are in portrait or landscape, and does not care if you are panning horizontal or vertical. It just does what is best for the situation if a pan is detected. That means you also could be looking straight up, and panning one direction, and it would adjust for that. It also means that you can leave the mode switch on 2 all the time, and still get the same full IS in both directions, but it will automatically change to pan mode as required. There is no question all this is complicated to explain, and the Canon information is not real clear on it all, but that is the way it works.
You should try some planned pan shots some time to check out how effective it is, and get an idea of what creative effects you may want to try.
Thanks for the responses. Roland's post brings to mind Adorama's desk clerk advising to leave IS on 2 for movement of the lens in various orientations. And at that moment, I thought he was misinformed (though remained mum), such that option 2 is only for panning.
