Originally Posted by caddy-shak`
I'm looking at buying the panny AX100U
According to the calculator, to get a 126" diaganol picture, my throw range is between 12 - 25'.
If I'm reading it correctly, with no zoom (1x) I need to mount at 25'. If I move the projector closer to the screen, I will need to zoom to achieve the same picture size?
So, is it better to zoom or not to zoom? What are the pros and cons?
The thing to keep in mind too is that you're going to lose fL no matter whether or not you zoom or locate the projector further away and use less zoom. The key to fL is the square footage covered by light, and the larger your projected image, the less lamberts you have per square foot, and thus it will appear dimmer.
I've noticed no difference in picture quality in using the zoom versus locating my InFocus IN72 further from the wall (I didn't see the change in brightness vs. CR as mentioned by Wet1). The fact that the light travels through all the zoom lens elements whether or not you're actually 'zooming' means that you can expect the same picture quality unzoomed as you would when zoomed (except possibly at the maximum zoom where the picture can get a bit soft at the limits of the lens' mechanics).
The only time you'd notice a difference in the quality of the projected picture would be using a fixed focal length lens (non zoom) and accurately positioning the projector at a fixed distance from the wall to get the desired picture size. A fixed focal length lens has fewer elements (i.e. internal glass lenses) and thus there is less abberation in the enlarged image, and less light fall-off due to the light traveling through the inner lens surfaces.
However, this would not be ideal, because, as you've discovered, with a fixed focal length lens you'd have to have the projector 25' from the screen, and for the majority of households, this isn't practical. Most probably have a 10' to 15' limit on distance, so adding a zoom lens to the projector addresses this problem.
So, your best bet is to locate your projector somewhere between the maximum distance, and 3/4 of the way to the minimum distance. In your case that would be somewhere between 15'4" and 25'. Or you could always settle for a bit smaller screen size, but who wants to do that?
So really, the only 'pros and cons' you have to worry about are screen size vs. picture dimness, rather than the pros and cons of zoomed vs. unzoomed pictures. One is a very real tradeoff, whereas the other is fairly negligible in the overall picture, IMO.