[photo-3d] Splitting hairs (was Beam splitters vs. Image splitters)

[Gabriel Jacob <3-d@xxxxxxxxxxxx>]

The "championing" of proper terminology is as old as 3-D itself. Actually
this EXACT discussion has been "championed" by others, many years
ago, and no doubt by others before that. Of course many others will come
on to the scene to take over this worthy cause!

On another matter, if I have quoted the WHOLE thread, it is to illustrate
a point about quoting messages! Your loosing your audience if you
don't get edit your quotes. As to the probability of misquoting and taking
something out of context, the lesser of two evils is your recipient missing
the point your trying to make. Your reader is not going to wade through
a long list of unedited quotes to find what particular issue your
addressing.

Gabriel

At 10:40 PM 1/9/01 -0500, you wrote:
>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
> >
> >
> >
> >