Beams, the manipulation of

[P3D Neil Harrington <nharrington@xxxxxxxxxxxxx>]

Gabriel Jacob writes:

>>Neil Harrington writes
>>It's probably possible to get into yet another word-hassle over "beam," but
>>I'm reluctant to do so.  I'll settle for pointing out that "beam," the verb,
>>does not really carry the same meaning or implications as "beam," the noun.
>>It is correct to speak of sunbeams, for example, but the sun does not _beam_
>>light in any one direction as a headlight does; it radiates pretty equally
>>in all directions.  A beam of light, whatever the source, is a directional
>>thing practically by definition, but that doesn't mean or imply that the
>>source was directional.
>
>Well guess what I have beammed the Sun! Very easy to do also.
>Just take a mirror and you can beam the Sun in any other direction.
>Thus you achieve two objectives. First you redirect the Sun light 
>and you create a Sun beam.

Well, actually it was the sun that created the beam, but otherwise . . .
Sure.  Don't even need the mirror.  Any small opening that lets sunlight
into a dark room would similarly give you a sunbeam.  The important point
here is that the beam is _directional_; every photon in it is moving along a
path essentially parallel with the path of every other photon.  As a
_source_, however, the sun is not directional at all.  This is the
distinction I am making between "beam" the noun and "beam" the verb: they do
not necessarily imply the same things about the source. 

>Now getting back to 3d thing a ma jig we are trying to define, it is
>called a beamsplitter. Technically might not be correct but it describes
>what in effect it SEEMS to do. Since most of us know what we are talking 
>about when we call it that in a 3d context, I think it is therefore correct.
>A 3d beamsplitter describes what it achieves and not what it does.

Uh . . . howzat again?     :-)

>As others have said and I will add to it, it does not split any beams but

Yup.  My point all along.

>in effect it takes different beams and redirects it to one lens. A 3d camera
>has two lenses, so it just intercepts those two beams but a beamsplitter 
>converts a single lens to intercept two beams. It seems that the 
>beamsplitter took a single beam that the one lense camera would see and
>introduced to it two beams. Its true they are not identical beams and
>therefore never split, 

I agree with most of what you're saying up to this point.  On just one point
I would make a correction:  The mirror attachment doesn't "[take] a single
beam that the one [lens] camera would see" and do anything with it, because
any single beam that the one-lens camera _would_ have seen never becomes
part of the process at all--it falls between the two outer mirrors and
therefore doesn't contribute anything to the image on film.  What the mirror
device does is intercept the separate and different beams that _would_ have
gone to two separate lenses in a conventional stereo camera, and redirect
them so that they pass through the existing single lens.

Thus, if anything, the device would be better called a beam-joiner than a
beamsplitter.  But I'm not seriously suggesting that as a replacement, I
hasten to make clear.    :-)

>Now would a Loreo camera be considered a beamsplitter. 

Not by me, certainly.

>Oh no we
>are digging a big hole here now. No it would not be considered a
>beamsplitter camera because it uses two lenses. It does use
>the beamsplitter arrangement that is used to convert single lense
>cameras but as I said it uses two lenses therefore it uses the
>beamsplitter arrangement for a different purpose. 

You see, this is exactly the problem with accepting incorrect terminology:
it leads to and encourages further incorrect terminology.  _Why on earth_
would anyone call the mirror arrangement in a Loreo camera a "beamsplitter"?
All the mirrors do in a Loreo is extend the stereo base.  The optical paths
are entirely separate from each other until they reach the film plane.

>Incidentally I have used the Pentax beamsplitter

Do me a favor and take out the manual that came with your Pentax STEREO
ADAPTOR. Now look through it carefully, page by page, and see how many
occurrences of the word "beamsplitter" you can find.  I can give you the
number right now: zero.  The manual repeatedly refers to the device as a
Pentax Stereo Adaptor, and nothing else.

>with a video camera and
>it works pretty well. I had a problem to view it with my 27 inch set so
>I took my stereoscopic viewer and looked at it with my 4 inch black and
>white set and lo and behold I had 3d video!

Hey, that's really interesting!  I'll have to try that myself.


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