Jerry Finnerman was the director of photography (except for the last part of season three). He'd be the one picking which camera to use and how the lighting should be for each shot, based on the effect the episode director wants to achieve.
Ralph mentions the 9mm was Jerry's idea (from senensky.com):
Ralph Senensky wrote:
I decided I wanted to use the fish-eye 9mm lens again, the lens Jerry Finnerman introduced me to on METAMORPHOSIS