the limit is the size of the display unit inside the projector.... gotta remember, inside the projector is a transparent LCD display that is really small. the light shines in through it to project the image on to the screen... most mid-low end projectors are SVGA (800x600) - i'm lucky enough to have picked up a "cheap" (£400) projector a few years ago in a sale that is XGA (1024x768) which does make a huge difference.