It's not clear whether by "adjusting the light/focus" you're referring to the resulting movie or whether you're referring to the effect of the light sensor (next to the camera) dimming of the monitor/screen?
If it's the first then this seems strange - are you wanting to keep images under or over exposed? Someone else will need to help you on this... and it probably is either buy something commercial or include the phrase "open source" in your web search.
The second... you'll find in system preferences "Displays" and at the bottom there (easy to miss) a tick box labeled "Automatically adjust display brightness as ambient light changes". Un tick the box and you are master of the brightness of your screen.
Hope that's helpful.
4I want a nerdy solution, not a commercial app. I don't want to pay for using a webcam! – George Profenza – 2010-03-12T02:41:51.097
I don't think you understand what webcams are for. – Hasaan Chop – 2010-03-12T06:09:35.087
@NSD what do you mean ? What are webcams for ? @fideli - fair enough – George Profenza – 2010-03-12T14:10:16.657
2They're for making college kids really angry apparently. – Hasaan Chop – 2010-03-12T23:56:58.947
George, @fideli won't get notified for your "at". Only the first one on each comment will get a notification. It's just how things work today. – cregox – 2010-03-13T02:41:59.677
@NSD I don't see how your comments are of any use. If apple says the webcam is only to be used with one purpose, do you have to agree ? if your hardware can make a lot more than your software allow it, should you close your eyes and pretend the posibilities aren't even there ? It's like saying 'I write software, but I only use APIs and never write my own. I just do what is easy to do.' – George Profenza – 2010-03-13T13:59:49.097
Might want to tag this as opencv as I, too, was doing some OpenCV stuff. – Qix - MONICA WAS MISTREATED – 2015-09-10T19:48:55.137