Originally Posted by seafan
I'm looking to get a projector mounted in the ceiling of a media room. Using the projector calculator (BenQ W1070 as an example), it shows that for 125" screen, with 10ft ceiling, 2'8" from floor to screen bottom, the projector should be mounted at 10'5" from the screen at 1x zoom. the room is 17ft long with pre-built conduit and outlet for the projector, which is closer to 14ft from screen. If I mount the projector 13ft from screen (to avoid longer exposed cable and power cord), to get the same size picture, I would need to use 1.25 x zoom of the projector (the max zoom is 1.3). Would that degrade image quality (by pushing zoom almost to its max)?
The short answer is 'most likely'.
The long answer matters though, because there is no such thing as 'using zoom' on a projector. More accurately, there is no such thing as NOT using zoom. A projector which has a zoom lens is zoomed in, zoomed out, zoomed midway, zoomed 3/4 in or out... If you have a zoom lens, then you are using it all the time.
Now, a VERY good lens will have minimal impact on the quality of the image across the entire range of the lens. Shorter zoom range lenses, like those of the BenQ, will have less impact on image quality than those with a long zoom range, like the Epson 5020 or Panasonic AE8000.
But, there is no guarantee that the lens won't introduce some distortion across the zoom range.
My general rule: Don't use the extents of the zoom range. So, with the BenQ you have a throw ratio of 1.15:1 to 1.50:1. I would try to put it at least 10% to 20% off the extents. So, if your range was 11.5' to 15', then I would shoot for about 12.5' to 14' as my lens to screen distance.
Now, most projector lenses also decrease in brightness the further the lens is from the screen. This impact is far greater on the long zoom projector lenses than it is on the shorter zoom lenses like on the BenQ. So, I wouldn't worry about this at all.
I'm running the 1070 on a 161" screen and I don't see any visible difference between having the projector towards the front of the zoom range or at the back of the zoom range. I have not looked with a critical eye at image quality at either extent.