I am very new to all this, so sorry if this is a daft question: I would like to calculate the image size thrown by a particular projector at a particular distance. Is there a way of doing this, or alternatively is there some sort of calculator out there somewhere, or is it adjustable with the lens? E.g. Sharp XV-Z7000 Projection size 40" to 250" (from Sharp site) - but at what distances? Thanks for any help!