Re: How rare are curved cinemascope screens?
- From: Martin Hart <notlookinf@xxxxxxxxx>
- Date: Mon, 31 Jul 2006 03:07:27 GMT
In article <K15zg.6755$bP5.6536@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
screen@xxxxxxxxxxxxxxxxxxxxxxx says...
Actually, the sharper picture, at least for large screens with wide
aspect ratios, is a slight curve. Otherwise the edges of the screen are
further from the projector lens than the center.
Yes but that's not automatically true. It may in fact be true but it
depends on the optics.
What I would like to know is when they show one of those ray tracing
diagrams in a book, you know, the ones with the drawing of a candle as the
subject, is the focal plane (the place where circle of confusion = 0) a
plane on both sides of the lens or is it some non planar shape like
spherical or parabolic. I would take this to be the "natural" situation
and then real world, complex, multi element lenses deviate from it by
design or maybe not.
There's ample evidence (cite: empirical data by Steve Guttag for example)
that the real world projection optics result in a curving focal plane. But
is this by design (or a byproduct of the complex lens system) or is a
manifestation of how all lenses are (unless the design specifically alters
it) and would be true even with the simple lens of the basic physics books.
Dating back to the introduction of CinemaScope and the Miracle Mirror
screen, the curvature was more to direct the screen light back towards
the center of the audience than it was to provide any great improvement
in focus. Some slight curvature of the plane of focus was apparently the
common way that projection lenses operated unless built specifically for
a wide flat screen. I used to use Kodak projectors with lenses that were
for flat screens.
Marty
--
The American WideScreen Museum
www.widescreenmuseum.com
.
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