what is the distance betwen the front of the lens of the projector to where your screen is going to be ?
just measure that distance and divide by 1.5
i have an 8 ft dual masked screen and it is 12 feet from lens to centre of screen, so you have more than enough space for an 8 ft screen.
I have based this calculation on the assumption you have a crt,
Thanks for your replies, but I wasn't really asking about the projector restrictions of size, i was more interested if you were sitting 4.5m (14.7 ft) away how large would you like the screen. Another way of asking it is whats your prefered angle of view?
At the cinema some people like sitting right at the front and others all the way at the back and most somewhere in the middle.
The minimum angle of view for a THX cinema is 26 degrees for the farthest seat with 36 degrees recommended. I just worked my angle out at 31 degrees which I feel is too narrow, the screen seems distant and not immersive enough. The problem is if I sit too close I get the screendoor effect of the PJ.
You also want the bottom of the screen to be below eye height if possible it makes a huge difference IMO.
I find that having to look up at a screen too much makes me feel uncomfortable. I sit with my eyes about a third up from the bottom of the screen, and that feels very comfortable. I may consider lowering the screen a little to improve this further, but my subs and center sit under the screen so I could only do this by a few inches at most.
Here's a link that might be useful regarding distances and viewing angles for those who might be interested: