Film-Tech Forum ARCHIVE: Screen Curvature

This is topic Screen Curvature in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Iben Jimenez (Member # 3713) on 04-07-2006, 12:27 AM:

Hi everybody.
Congratulations for your great site. I'm very glad of being a new member and here is my first question: What is the purpose of the curvature in the movie screens? More even illumination?, To avoid pincushion effect or barrel effect? or All of them?. What about torus or toroid screens(horizontal and vertical curves)?

Posted by Monte L Fullmer (Member # 2797) on 04-07-2006, 02:59 AM:

Basically, a curved screen, especially with scope movies, will allow the ends of the picture to stay in focus since the image corners being as such an angle and distance from center of lens will have a tendency to be a bit out of focus than the center of the picture. Thus with the ends of the screen being curved, shortens the throw length to lessen the chances of out of focus at the ends..

.have to ask others on the other questions...Welcome to Film-Tech.

Posted by Bernard Tonks (Member # 809) on 04-07-2006, 06:18 AM:

Links.

Torus Screens

Curved Screens Vs Flat Screens

Curved Screen & Focus

[ 04-07-2006, 05:58 PM: Message edited by: Bernard Tonks ]

Posted by John Pytlak (Member # 331) on 04-07-2006, 09:20 AM:

The primary reason for curving a gain screen (per SMPTE Recommended Practice RP95) is to optimize uniformity of screen luminance as viewed from the primary seating area of the theatre.
A gain screen acts somewhat like a mirror, and follows the law of reflection (angle of incidence = angle of reflection). So the curve and tilt of a gain screen should ideally be determined by ray-tracing, so the projected image is reflected to the prime seating area from all parts of the screen surface. SMPTE RP95 simplifies this in the formula:

(Projection Distance + Distance between screen and audience center) / 2 = Radius of Screen

A low gain (matte surface) screen should NOT be curved, as it reflects light equally in all directions, and curving it may reduce image contrast.

Of course, special processes like Cinerama and D-150 were designed with the concept of a "deep curved" screen that more fully surrounds the prime seating area.