On most professional camcorders, they have this black rim around the lense, I would assume its to omit surrounding light from entering the lenses. They have them on for example a Canon GL2 and 1. I want to know so I would be able to buy an external one to add to a Panasonic GS-500
Here is an example of what I mean.
http://wize.com/photos/small/18473.jpg