Re: Shift lenses

[P3D William Carter <wc@xxxxxxxxxxxxxxxxxxx>]

John B. asks about using wedge prisms, as opposed to falls, on his 
projector lenses...

Keep the film plane parallel to the screen.
As the projection beam is steered through a prism it acquires a keystone 
distortion parallel to the beam. This distortion is then neutralized by 
the screen being parallel to the film plane. 

This is the method used at theaters which project at to high an angle to 
to mask the keystone distortion with the proscenium.

Melles Griot has the formulae for an apex angle for a chosen deviation.

-- 
                wc@xxxxxxxxxxxx
    37deg 39.09'N x 122deg 29.56'W x 90'MLLW





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End of PHOTO-3D Digest 1481
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