Practical FPTV screen size..? (1 Viewer)

[Trevor Schell]

Hi!,
I was just measuring up the size of screen I would go with.
The two chioces I had are as follows.
92"Diagnol (45"x80")
106" Diagnol (52"x92")
Of course my first choice is the 106". This will actually completely cover my Entertainment unit which is 94" wide,2 inches wider than the screen size width. The screen would be mounted directly from the ceiling in front of the Entertainment unit.
However,,would this be too big of a screen to veiw with the seating area at 16 feet away from the screen.?
Would the 92" be more practical?
Is there a certain height limit from the ground to the bottom of the screen that should be allowed?
I would also need to go with a THX acoustically treated screen which is made of the Micro-perf material since my center channel would need to be behind the screen.
Thanks,
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Trevor..

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[Guy Kuo]

A screen width which subtends a view angle of around 30 degrees is about ideal for HT viewing of NTSC video. Wider than that and the image begins to reach the size at which the limited resolution of NTSC video begins to look too soft. Smaller than that, and you start to lose the immersive effect of a theatrical screen. With your stated 16 foot viewing distance and larger screen size you have a subtended view angle of
26.9 degrees or 2 atan ((width/2)/(viewdist*12)) 180 pi
where width and viewdist are in inches.
Given that the subtended view is near 30 degrees, your proposed larger screen is a reasonable size provided the projector is one which can handle that large of a screen and still hit at least 14 or better footlamberts. You might even go larger on the screen to reach a 30 or slightly higher view angle. This presupposes a digital projector. A CRT projector may have difficulty with generating sufficient light output for the larger screen sizes.
On my own system I have a subtended angle of 34 degrees. The image is definitely not too large. Your proposal won't be too big at 16 feet. Bear in mind that the larger the screen, the more critical that the projector, video processor and source be of good fidelity.
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Guy Kuo
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[Edited last by Guy Kuo on November 12, 2001 at 01:43 AM]

 

[Sean M]

Not that there's any need for me to second Guy's opinion, but, that screen size is just fine. You may wish to demo your planned projector (or projector/processor combo depending on which pj you select) with a micro perf screen before making a final decision, if you go with a digital projector. Some digital projector display a moire pattern on microperf screens so you'll want to check for this. You may have trouble going with a CRT at that size and microperf (not a problem if you've already decided to go digital) since I don't recall anyone making a moderate gain (1.3 - 1.8 after the 10% light loss for the perf.) microperf.
An average 8" CRT will give you 220 ANSI lumens (800 - 1100+ peak) which, after accounting for the light loss on a 1.3 gain (before light loss) microperf yields about 7.7 ftL at the screen. Not bad, but not great. Whether this proves bright enough is up to you. You want to shoot for a minimum of 9 - 12 ftL. under ideal conditions. But, the brighter, the better.
The Sharp 9000 would give you 16 - 20 ftL depending on mode, assuming a Grey Hawk microperf.
I've done all these calculations assuming the 106" diagonal screen size. You probably don't want to go any smaller than that from 16'. But, be aware, as Guy said, the projector and processor become increasingly more important that larger the screen is, or the closer you sit (same difference). After seeing the 9000 with a progressive signal, I really don't think you'll need to process it further. At least not initially. Once you get used to the picture and start picking out flaws, you may want to add a scaler like the Faroudja NRS since they make a mode that fits that projector's resolution perfectly.
Edit - I went back and ran the calculations on the 92" screen size for a 1.3 gain microperf screen with a 220 ANSI lumen CRT and got 10 ftL, which should be bright enough. The question is, larger screen, slightly dimmer, or smaller screen and slightly brighter. Given the choice, I woul selet the larger, slightly dimmer screen. The peak brightness in most scenes is still going to be more than enough to give the picture snap. You'd be surprised how bright 8 ftL is a completely dark room is.
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"Experience is the one thing you can't get for nothing." - Oscar Wilde
[Edited last by Sean M on November 12, 2001 at 08:38 AM]
[Edited last by Sean M on November 12, 2001 at 09:02 AM]