P3D Re: Projection and mounting

[Kenneth Luker <kluker@xxxxxxxxxxxxxxxx>]

> If a "standard" alignment slide were created such that the supposed infinity points were identified in each frame, and the projected image of the alignment slide were to be manipulated using the projector's horizontal control so that the two points were physically
> separated on the screen by the nominal inter-lens spacing of the projector, then it wouldn't matter how far away the screen is, or how large the screen is.  A mile-high screen a mile away would intercept the parallel lines extending from the projector toward those
> infinity points in the same way as a two-foot high screen in the same room:  the infinity points will be at the same separation on ANY screen, if the lines from the projector to those points are parallel to one another.   If the inter-lens spacing of the projector is
> about the same as the inter-eye spacing of the viewer, then there is no problem.

It's true that the mile-distant screen would have the two infinity points so close together that one couldn't resolve them separately without a telescope, but the rays from those points into the eyes of the viewing person would still be parallel.

My point is that all the projectionist must do is make sure that at setup time, the infinity points at the screen are at human interocular separation.  Then, any slides that have been mounted with infinity separation that match the standard calibration
slide's infinity separation will be viewable with no need for adjustment and with no discomfort.  The problem is that slides mounted "to the window" without consideration of the infinity points will sometimes have faulty infinity placement.  As a safe compromise, I'd
say, mount to the window but ensure that the infinity separation isn't violated.   The "far-point" line on the mounting gauge let's one do just that.

Ken Luker