Re: [photo-3d] Beam splitters vs. Image splitters

["John A. Rupkalvis" <stereoscope@xxxxxxxxxxxxx>]

----- Original Message -----
From: "Ron Beck" <rbeck@xxxxxxxx>
To: <photo-3d@xxxxxxxxxxx>
Sent: Tuesday, January 09, 2001 2:57 PM
Subject: Re: [photo-3d] Beam splitters vs. Image splitters


> Okay, I'm confused now.  How do you get a stereo pair with a beam
> splitter and two cameras at right angles to each other.   I understand
> how the "image splitter" works in that it has a left side and a right
> side which are exposed on the negative.  However a single "beam" of
> light, split in two provides the same image on both negatives.  Where is
> the horizontal disparity with a beam splitting device?
>
> Where did I get lost in this?
>
> Ron
>
It would only provide the same image if both cameras were coincident.
Actually, it is splitting not just one beam of light, but all beams of light
that strike the surface, sending nearly half of the light through it, and
nearly the other half reflected at 45 degrees from it.  Therefore, it is a
relatively simple matter to displace one camera laterally in relation to the
other for whatever stereobase you want within the size limitation of the
beamsplitter.  You could center them normally for orthostereo, or wider for
hyperstereo, or narrower for hypostereo, including extreme closeup macros
with stereo bases of only a few millimeters.  Of course, if you continued to
bring the optical axes of the cameras together until they were perfectly
aligned, you would have a stereo base of zero, parallax of zero, and indeed
the pair would be monoscopic, not stereoscopic.  But then, you wouldn't want
to do that, would you?

However, I would.  Why?  Not for still, but for motion picture or video
applications.  I start at zero, and increase the stereo base to normal or
whatever I want.   The result in full motion on the screen is that of a
conventional flat, monoscopic image magically transforming into a full
three-dimensional stereoscopic image while you watch.  A great way to start
a production, and it never seems to fail to make the audience gasp in
surprise.

JR

> pd@xxxxxxxxxxxxx wrote:
> >
> > ----- Original Message -----
> > From: "Bryan Mumford" <bryan@xxxxxxxxxxxx>
> > To: <photo-3d@xxxxxxxxxxx>
> > Sent: Tuesday, January 09, 2001 12:41 PM
> > Subject: [photo-3d] Beam splitters vs. Image splitters
> >
> > > If you are willing to educate me further, I'm curious why beam
> > > splitters are used in photography. Why do you wish to capture the
> > > same scene on two cameras?
> >
> > The same could be said of stereo photography in general:  Why photograph
the
> > same scene twice?  The fact is that with two cameras at nearly right
angles,
> > and a suitably placed beamsplitter mirror, you can get stereo pairs, and
you
> > can vary the spacing and "toe" in ways that the sizes of the camera
bodies
> > would not allow with normal twin rigs.
> >
> > -pd
>
>
>
>