Originally Posted by Lone Granger
I have waded through this thread and naturally thank all contributors - that is a way of saying - if i ask a dumb question I should know the answer to now, I apologise in adance..!
The proposed room set-up: 15' wide, PJ Throw 15', viewing in the 15' to 18' distance (room 19' long) - viewing width max 10' - PJ easy height to mount would be 6' 6" in an 8' high room.
Proposed PJ is the new JVC HD D-ILA HD1 or perhaps the Pearl.
Preferred screen width is 12'All
surfaces of room satin beige.
Screen of preference (havent checked price yet..) from recommendation here is the DaLite HP - however is max width really only 106"?!
I can presumably set PJ to fire up at target wall to set screen height at say 6" below ceiling (6" above floor)
I am looking for a punchy, refreshing image more in line with LCD displays than Plasma / traditional front mount PJs - ie I am happy to 'sacrafice' the full Cinematic effect - I am not a 'full black junky' and would be happier to be stunned by vibrant refreshing images with detail in dark areas than go on a 'black-hole' quest.
I am not sure what Fl this equates to - does 20 sound about right?
If so with say 650 Lumens available from PJ for best part of 1st year (then replace bulb) and a 87 sq ft screen, I have a theoretical target of 1740 adjusted lumens. - ie a 2.7 gain in screen brightness - am I right? - If so then the DaLite @ 2.8 would appear to fit the bill perfectly (still not checked price..)
So, if i am correct so far, the only remaining concern is the angle of incidence / reflection from PJ to a central viewer. - Even if we assume viewer is directly under PJ (prefer 3' further back) - ie viewer is 3' 6" to 4' lower than lense, and nearly 1/2 way up screen height (mid screen ht is 4') - dont know how to do diagrams on here so hope you can see where i am going.
Now then, using an approx scaled diagram and no ability or knowledge retained on logs and in absence of protractor I calculate that, vertically, the bottom of the screen is viewed 15 degrees below PJ line of incidence (halfway toward the line of reflection) - whereas the top of the screen is viewed 12 deg below PJ line of incidence (in the wrong swing from the PJ line of reflection)....
Sooo, now I am not too sure if I should worry about an Angular Reflective or regular screen (both 2.8 gain)...!! -- It would seem to me, the layman that I am vertically off axis by a max of some 15 dgrees at the bottom and that the bottom is an error that an Angular reflective would address whereas the top is negative Reflective - if you see what I mean!
If you feel that this set up is outside performance envelope of a reasonable cost screen to give excellent performance, then i guess I could drop PJ a foot without much hassle (I intend sliding it on rails to side of room into a wall cabinett for stowing) - just dont want it whining away a foot above your head in height and 3 ft in front!
Have i grasped all this theory correctly, am I really creating a problem of 15 degrees or do people simply measure from mid screen to PJ and to eye - I cant help but think that a 10 degree off axis screen will be a problem for the lower 1/3rd of my screen based on my interpretation of these formulae
This would appear to be a classic set-up other than the fact that i am looking for a vibrant image over 12' width with c 650 Lumens PJ
Clearly reducing to a 10' wide screen would mean that I only require a gain of 1.7 - presumably I could get well over 15 degrees deviation here (not re-drawn smaller screen in this room set-up to see how angles change mind) - though I couldnt see it in reviews
Am I screwing the theory somewhere?!