Locking Your Webcam's Exposure with iGlasses
Most webcams automatically adjust exposure and color balance in order to deal with different lighting conditions. This is usually what you want, but there are situations when you don’t want the exposure to change. For example, if you’re making a stop motion video (with something like iStopMotion), then you don’t want the camera’s exposure changing between snaps. (Manual focus comes in handy here too.)
Or if you’re doing a chroma-key, you can’t have the camera’s colors adjusting when you step into the frame, or it breaks the key. Also, sometimes the exposure isn't right because you have a bright light behind you.
Look at the bottom of the Adjustments tab for the “Exposure” Auto/Manual slider. This will only show up when using a compatible camera. Compatible cameras include most UVC webcams, the built-in iSight/FaceTime cameras on most Macs, and the camera inside Apple’s Cinema Display.
You can also lock and adjust White Balance and Focus on supported cameras.