I use wide angle lenses a lot when photographing interiors of abandoned buildings or in cathedrals/churches. I could not have done without my Maxwell screen. I still have trouble focusing in very dark interiors, and in trying to see if I have stopped down enough. I bought a 75 mW green laser to aid in focusing, and it is a real winner. As some have pointed out the switch has to be depressed to keep on; I resorted to using a rubber bumper (found at hardware store and used to prevent frames from scratching walls etc) attached to something like a paper clamp - hits the button just right. To attach it to the camera I got a Kensington document holder from Office Depot (http://www.officedepot.com/a/product...ip-Copyholder/. Cheap too at $10.

Mike