I have a Canon 500mm f 4 lens that has three image stabilization modes. I have mine set to '1' and leave it there for all applications. I shoot sometimes from a hide, sometimes hand held, bush walking and occasionally have a go at BiF. It seems to work well enough. Embarrassingly, I must confess that this is mainly because I can't really understand what applications the modes are meant to enhance. Can anyone explain the purpose of the three modes and how each might relate to bird photography?

Hello Michael,
Mode 1 is two axis - horizontal and vertical and general purpose for perched birds .
Mode 2 is vertical axis only and used for panning such as birds in horizontal flight..
Mode 3 is two axis - horizontal and vertical but only actuated when the shutter button is fully pressed.
I only use modes 1 and 2. I use Mode 1 for perched birds and Mode 2 for BIF. I have not found any advantage in using Mode 3 but I would be pleased to learn if anyone has found this mode has some advantages.
Kind regards,
Ian

Hi Ian,
Thanks very much for taking the time to explain these functions clearly.
Regards
Mick

There seems to be some conflicting advice on the internet about the use of Mode 3 but I have found this article to be helpful and agrees with what Ian has said above : Canon Europe article
I have used both mode 2 and mode 3 for birds in flight but haven't had enough experience with them to say which is better. When you are tracking a bird in flight the motion isn't really fully horizontal or vertical (diagonal) so in theory mode 3 should be better. Because it only acts when you fully push the shutter it should also allow you to track the bird better. Ian - have you found that the viewfinder image jumps around in mode 2 when tracking a bird ?

For static birds I usually swap back to mode 1 if I remember to change the switch . I must say that using mode 3 is vaguely unsatisfying as the viewfinder image is not stabilised as in mode 1 and it makes me wonder if the stabilisation is actually working (but that's just me)

Chris

An interesting and helpful article Chris, thanks.

Thanks Chris, a very useful contribution. I find Mode 2 better for tracking BIF because it helps to remove up and down tracking error and keeps the bird more stable in the viewfinder. I usually have my lens set with Mode 2 so that it is ready for taking a flight shot at a moment's notice. I forget to change to Mode 1 for perched birds and most of my images are captured with Mode 2, both perched and flying.
Cheers, Ian