I'm working in a high school that has a ceiling-mounted projector in the tech booth that hits a screen that comes down in front of the stage. I'd like to use that for supertitles in Thoroughly Modern Millie, but just access the top-most portion of the screen - and block out all the rest of the projected "black" that will bleed onto the stage below. So, I'm planning a manual dowser that essentially works like an ellipsoidal shutter to block the lower portion of the projection. Since we won't need all of the projector image in the show, the manual dowser can be set and left throughout the show. My question is: What is an appropriate distance from the projector lens for the dowser to be in play? I've never used the DMX dowsers (ie. http://www.citytheatrical.com/products/-projector-dowser), so I have no reference. The manual for the CT instrument just says "as close to the projector lens as required." Any guidance?