"Beamsplitter," the inaccuracy of Message-ID: <1.5.4.32.19960823183712.006b21dc@xxxxxxxxxxxxx>

[P3D Neil Harrington <nharrington@xxxxxxxxxxxxx> To: photo-3d@xxxxxxxxxxxxxxx]

Marvin Jones writes:

>"Beamsplitter" or "framesplitter" neither one betrays any Greek roots, so who cares? The whole discussion strikes me as fairly specious, anyway. Despite many arguments to the contrary, as Larry rightly pointed out the other day, the device really DOES "split" beams. Light is beamed back to the camera by the 

Oy. Marvin, you are piling more freight on the back of "beam" than the poor unfortunate word should be expected to carry. 

Light is not "beamed back to the camera" in any reasonable sense of that word. You might say light is beamed by a flashlight, or headlights, or the optical system of a projector, or anything else that concentrates and directs light in a certain direction, just as a radio transmitter with a directional antenna beams radio waves. That doesn't at all describe the situation with light from any ordinary subjects. I cannot remember ever having taken a picture of any kind in which the light was _beamed_ into the lens(es) of my camera.

A beamsplitter takes an existing beam (or ray) of light and splits it, sending part of it in a different direction. That's what a beamsplitter does. It isn't what a mirror stereo attachment does. Every single beam (or ray) of light that enters a mirror stereo attachment goes its own way, reflected and then refracted en route to the film plane, but never split, sliced, cut, divided, separated, centifruged, or otherwise partially removed from itself.

>subject, and is gathered up by two separate lenses and manipulated onto the 
film
>plane in a multiple-image configuration quite different from the information carried on the original beam. For my money, that's a beamsplitter pure and simple.

Then for your money, any stereo camera is itself "a beamsplitter pure and simple," since it does what you have just described just as much as any mirror stereo attachment does. Not for my money, though. 




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