Beaming light

[P3D Larry Berlin <lberlin@xxxxxxxxx> To: photo-3d@xxxxxxxxxxxxxxx]

>Neil Harrington writes:
>Light is not "beamed back to the camera" in any reasonable sense of that word. You might say light is beamed by a flashlight, ....... 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.

*************** Then you never took a photograph???!!! Light had to enter your camera or the film woudn't have been exposed. ; -) I agree that it is stretching definitions a bit but there is a specific cone of incident light that enters the lens and falls on the film. In a single lens camera there is a single cone of that light. With a mirror attachment on that single lens device, the usual single cone (loosely called a *beam* for purposes of discussion) is formed into two beams which enter the single lens providing the two images of a stereo pair.

Note that the definition quoted by Bob Howard officially includes the use of the word *beamsplitter* to refer to a device for creating a stereo image in a single lens 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.

**************** If you include all incident rays of light reaching the camera lens as a single *beam*, then the description does make sense and this normal single *beam* is essentially split into two paths. Yes, in a technical sense they are now separate paths and could be considered two separate beams, but the normal for a single lens device is only one such beam. Hence, the mirrored stereo attachment splits the single beam into two beams directed into the single lens.


>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. 

***************** Not true, since a stereo camera has more than one lens it could not be described as a beam splitter. It records a *two-beam* situation instead of one beam. Unless you add a mirrored attachment to split portions of the *beam* arriving at one lens to take it to the other lens and vice versa. Or add a mirror attachment (commonly called a beamsplitter) to each of the lenses providing each lens with a stereo pair image. ; -) 

Besides, if you wanted to be totally accurate to the terminology, you could devise an arrangement of reflecting surfaces with actual optical beam splitters which would sandwich the two images through a single lens. While it doesn't seem very practical by itself it might be useful for doing anaglyphic photography by using mirrors to capture the full view from two vantage points, filters to provide the color anaglyphic aspect and optical beamsplitters to combine the two into a full frame anaglyphic stereo picture in one step with a single lens camera. Does such a device already exist? Or would there be too much loss in the beamsplitter to get good exposures? 

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/


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