Re: preliminary summary on ghosting

[P3D John Bercovitz <bercov@xxxxxxxxxxx>]

Greg W. writes:

> The lenticules do not refract, only reflect.
> According to Da-Lite, their purpose is to reflect back towards the
> center of the viewing area, some of the light that would have reflected
> off to the sides if the screen were completely flat.  This design
> trades off useful viewing angle for a brighter image nearer the center,
> which happens to be a very useful trade-off for stereo projection.

Now that's funny; I thought the purpose of the ribs was to _spread_
the light so it didn't primarily go back to the projector.  But not
spread it too much, of course, since light to the wings doesn't help.  
Maybe both statements are true.  Where is that catalog when I need it?  
OK, here we go.  The white screen is approximately Lambertian having
the same luminance, essentially, out to 60 degrees (where the chart 
ends).  The other varieties peak in the direction of the projector,
which they call 0 degrees on the chart.  The one exception is the
lenticular screen which peaks 20 degrees off the projection lens axis
(where the projection lens axis is perpendicular to the screen).  So
the silvering returns more light ot the center and the ribs spread 
the peak out to make it more even for the area in which the audience
sits.

John B


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