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

["Stuart Stiles" <sstiles@xxxxxxxxxxxxx>]

With this posting, we have arrived at an effect of on-screen stereo image
generation right before the eyes of the viewing audience.  The first time
that I saw this was actually during a still image projection session where
Simon Bell and Bill Duggan orchestrated a twelve projector show for us.
That was a starting point in my son's interest in stereo projection.  It was
a powerful stereo theater effect.  The beautiful two dimensional blossom
suddenly took on the quality of a three dimensional flower as the
lap-dissolve process presented a stereo pair rather than a duplicate pair of
images.

This also addresses the qualitative difference in the experience of
stereopsis that is produced when the brain has a pair of optic images that
have retinal disparity (generated in photography by a stereo base
separation), as  distinguished from the experience of image fusion, when the
brain has identical images, coming from the eyes. In both presentations, the
brain fuses the two images into one; or it suppresses one, while attending
to the other.

Recall that in a stereoscope we are  viewing two two-dimensional images.

The old Underwood and Underwood Views a non-stereo card (8159) and a stereo
card of Easter Lilies (7360) demonstrated that the identical images pair did
not produce the stereopsis that the disparate pair produced.

To further emphasize the fullness of experience inspired by the stereo
image, the text on the back of the card instructs the viewer, "Looking at
the blossoms closely, as we do here, we can see the exquisite, frosty gleam
and glisten of the surface of those beautiful, recurving petals.  Se can
even see their delicate veining.  Notice how each petal is marked down the
middle, not as an ordinary leaf is marked with one main mid-rib, but in a
charmingly decorative fashion of its own..."  The rest of the text reads
like a part of the story of the birds and bees and blossoms.  Of  course,
the same detail can be seen in the two identical images.  The stereo pair
served as a context for a more "in depth examination of the qualities of the
flowers."  There is no text on the back of the card with the two identical
images.

This has been a good conversation!   This is the way education should take
place. Once in a while I used to start a class on the trail of learning by
encouraging the students to challenge each other's use of terms, as they
tried to explain an idea that the academic discipline presented them. I
guess that I started this whole thing by carefully avoiding any effort at
explaining the terms  "splitter," and "mirrors" when pointing to the
3d-quarium site.

As always, I learned as everyone debated.

Now, I have a better understanding of the image splitting process and the
beam splitting process.  But even more, I have come to understand the
dynamics of using a beam splitting system for stereo photography in the
sense that John has championed it. That would likely not have become clear
to me without this exchange.  Thank you all.

 The thread will continue, even if we do follow Peter Davis' suggestion of
moving along from a meeting of the minds with regard to the "splitters."
Now, we seem to be tracing down the other term "prismatic."

Stereoviewing is at the heart of our hobby. There are an amazing number of
ways that stereo images can be created.

Stuart


-----Original Message-----
From: John A. Rupkalvis [mailto:stereoscope@xxxxxxxxxxxxx]
Sent: Tuesday, January 09, 2001 8:59 PM
To: photo-3d@xxxxxxxxxxx
Subject: Re: [photo-3d] Beam splitters vs. Image splitters



----- 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
>
>
>
>