The brightness control on my new iMac 21.5 is driving me crazy. If you turn it down to 1/3 or so (via keyboard), within a couple of seconds after the adjustment (especially when iTunes is running), it'll dim completely to the lowest setting.

After the display has gone to sleep, it'll often return to full brightness not the original setting, and same on reboot or if adjusting up a bit higher.
Only a few minutes later do you realise your retinas are burning, not ideal when you are working on photographic images.

Anyone else have this problem? Running 10.6.7 at moment.

In (I think) the 'displays' system preference there's an option to make it automatically adjust the screen brightness to ambient conditions. have you tried switching that off? it could be being a bit overzealous, or the sensor (which in behind some tiny drilled holes on the top of the imac iirc) could be somehow sensing a change in brightness that's not true of the room overall.

Jon

Hi Jon, yes that seems to work ok when it's not playing up, especially when I put a light on at night, but it could be going wrong, I'll disable it and see how it behaves!

This got me too. I noticed in the day at 100% brightness the screen didn't seem that bright (I tend to have it on full to replicate lengthy sessions staring into the sun presumably because I'm solar powered like Superman) yet at night on 50% brightness it was burning my retinas. I'm came to the conclusion that the screen was adjusting to the ambient light so I just let it get on with it now.

On mine the ambient control just wasn't working properly (it dimmed to nothing, or ramped up to 100%, regardless of my previous settings), I disabled it as Jon suggested and it's been fine ever since, retinas still intact