Re: IMAX and famous people

[John Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Wed, 8 Nov 1995 07:41:04 -0600
>From: crhs@xxxxxxxxxxxxxx (Centennial Science Dept.)
>Subject: IMAX and famous people

>Second, why are they using liquid-crystal glasses in a film theatre
>setting? Isn't the frame speed too slow to prevent flicker, and wouldn't
>standard polarizing glasses do the job just as well? 

Liquid crystal material comes in different speeds. Some glasses are adequate
for 60Hz NTSC, and the CrystalEyes glasses run at 120Hz. 2D films in the US
run at 72Hz (24 frames per second, but each frame flashed 3 times to reduce
the perception of flicker). From previous posts, the Imax theaters that use
the liquid crystal glasses have a dual projection system, so it's possible
that the glasses are switching at 144Hz. (Anybody know for sure?) That would
result in very low flicker, though field-sequential stereo systems inherently
have problems with very fast motion.

>Finally, in the Reel 3-D catalog, there was a refence to circular
>polarizers. How can these be used in 3-D projection, and is there any
>advantage? I am familiar with their use in killing specular reflections in
>photography, but can't see the 3-D advantage.

I think John B already posted a reply to this - you don't get ghosting if
you rotate the glasses (at least if the polarization is truly circular -
I'm not sure what happens if it's elliptical).

Tektronix has a circular-polarized CRT monitor, which can be viewed using
passive circular-polarized 3D glasses.

>Brian Mason

John R


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