I am purchasing a screen that is 178:1. I am noticing that most of my DVDs are 235:1. What is projected on the rest of the screen? Is it black bars like watching a widescreen movie on a 4:3 T.V. or is it just blank canvas? DO I have to reset the lens on the projector every time I put a DVD in with a new aspect ration or does the projector automatically project the image onto the screen in the new format? I am going to be using a Benq 8700. Any help would be greatly appreciated.