Fw: [photo-3d] Telestereoscope

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

----- Original Message -----
From: "John A. Rupkalvis" <stereoscope@xxxxxxxxxxxxx>
To: <photo-3d@xxxxxxxxxxx>
Sent: Sunday, October 22, 2000 1:03 AM
Subject: Re: [photo-3d] Telestereoscope


> Some of the development of the terminology stems from the development of
the
> devices themselves.
>
> For example, what we refer to today as "field glasses" are simply a pair
of
> telescopes of usually modest power mounted side by side.  As such, these
do
> not alter the stereo base, and give little stereoscopic relief (impression
> of depth) at the distances at which they are normally used.
>
> What we today call "binoculars" is a short form of what were formerly
called
> "binocular telescopes".   Actually, the term "binocular" by itself simply
> means an optical instrument that has two oculars.
>
> The term is also correctly used to identify the oculars (lenses that we
look
> through) in a stereo microscope, a binocular microscope (which has two
> oculars but only one field lens), and even our own eyes.  When I refer to
a
> field lens singularly, I am referring to a single optical lens system.
Such
> a "field lens" may be composed of more than one lens element, but if so
they
> are all coaxial.
>
> The word "ocular" originally was a medical term applied only to biological
> eyes, but later was extended to lenses that we look through to
differentiate
> them from lenses or lens elements elsewhere in an optical system.
>
> Stereographers have extended the application even further to refer to any
> stereo base, as in "interocular", although to be absolutely correct this
> should be called "interaxial" (distance between the optical lens axes),
and
> interocular reserved for the distance apart of lenses we look through, as
in
> stereo viewers.
>
> Since the term "interocular" has come into such common usage for general
> stereo base applications, and few people seem to understand "interaxial",
I
> often use "interocular" when talking to other stereographers, rather than
> the more correct term.
>
> The binocular telescope is an instrument quite different from a pair of
> field glasses, in that it also includes sets of prisms which have two
> functions.  They shorten the physical length of the instrument through
> folding of the optical path (for this purpose they are sometimes used in
> monoscopes as well).
>
> Perhaps of more importance to the stereographer, they also extend the
stereo
> base, allowing for improved depth perception at their normal working
> distances.
>
> The telestereoscope was simply an earlier term for what later became known
> as the binocular telescope, and in my mind is a more descriptive term.
>
> Even though we have shortened "binocular telescope" to simply
"binoculars",
> we still refer to them by a still longer term "a pair of binoculars" as in
> "a pair of scissors".
>
> A pair of binoculars is, however rather redundant, as the prefix "bi"
means
> two, or a pair.  If we still said "telestereoscope" it would be reasonably
> short, and certainly descriptive of the instrument.  Turning the subterms
> around, it might be even easier to understand if we called them
> "stereotelescopes".
>
> This last word has seen limited use in recent popular literature in
> reference to some of the very large, very wide base astronomical
telescopes.
>
> However, here, to imply that they are stereoscopic due to the wide stereo
> base is really stretching the meaning.
>
> Astronomical distances are so great that absolutely no stereopsis can be
> detected by the human eyes, as a result of the very wide stereo base alone
> (except, perhaps, within our own solar system).
>
> Rather these instruments are dual primarily for greater light gathering
> power and resolution (one instrument cancels some of the atmospheric
> distortions of the other).
>
> Stereopsis at astronomical distances is attained through either or both of
> two methods.
>
> Time parallax, in which two images are photographed through a telescope at
> two different times, allowing the earth to move within the solar system,
and
> the solar system to move within the galaxy.
>
> The other is computer evaluation, such as depth maps created from other
> depth information such as red shift (Doppler effect), etc.  This has
> resulted in some very spectacular stereoscopic astronomical imagery.
>
> JR
>
> ----- Original Message -----
> From: "Dr. George A. Themelis" <drt-3d@xxxxxxx>
> To: <photo-3d@xxxxxxxxxxx>
> Sent: Saturday, October 21, 2000 11:00 PM
> Subject: [photo-3d] Telestereoscope
>
>
> > >call it a telestereoscope.
> > >
> > >Checking my dictionary, I couldn't find this term, but on the
> > >net I found numerous references to it
> >
> > Gabriel, forget the net and open F. Drouin's "The
> > Stereoscope and Stereoscopic Photography" written
> > in 1894 :)  (Available from Reel 3-D, everyone
> > should have this book and read it!!!)
> >
> > Page 25 shows a picture of a Telestereoscope. A child
> > is using in a scenic view, as we use mounted binoculars
> > today.
> >
> > Drouin writes: "The Telestereoscope, invented by
> > Helmholtz, 1857, is an apparatus the function of
> > which is to increase the relief of distant objects
> > by enlarging the optical angle..... " etc.
> >
> > George
> >
> >
> >
> >
>