Re: [photo-3d] Digest Number 286. Mirrors

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

I find this an interesting comment, since beamsplitters are usually used in
applications where resolution is very important.

For example, we used beamsplitters in shooting the dual camera T2-3D for
Universal (and James Cameron is very fussy!).

The beamsplitter in the Hines rig, the Disney rig, the Universal rig, and
the Imax rig are all of superb quality.

Yes, the Imax rig. This often used in filming Imax 3D productions as an
alternative to using the Imax 3D camera (such as when the 3D camera is being
used simultaneously elsewhere).

I am wondering if possibly you are referring to an image splitter, a very
different animal.

I don't mean to ridicule, as this is a common error (I used to make this
mistake myself before finding out the correct use of the term).

Picky?  Perhaps.  But, only when everyone can agree on the usage of the
various stereoscopic terms can we discuss these things with each other
without misunderstandings.

I have been to stereo club meetings and conventions in various cities, and
often found individuals in heated arguments about such things as
convergence, beamsplitters, interoculars vs. interaxials, etc.

The interesting thing is that these individuals often were in perfect
agreement with each other, but didn't realize it.  The difference was
because of different interpretations of the same word.

For the record, a beamsplitter is a single sheet of glass (or, if small, a
specially coated prism).  It is similar to a mirror, except that the
reflective coating is very thin (in fact, it is sometimes referred to as a
two-way mirror).  Thus, when two cameras, mounted at 90 degrees to each
other, face such a beamsplitter (which is at 45 degrees to each camera), and
are set laterally to each other, the result is a (usually very high quality)
stereo image pair.

An image splitter is a device made up of a combination of 4 reflective
surfaces (either prisms or mirrors or both).  These are mounted as two
parallel sets, each set at 90 degrees to the other, and at 45 degrees to a
single normally monoscopic camera.

Thus the image (not the beam) is split in two, which indeed reduces the film
or other receiver area, and reduces the potential resolution, as Olivier so
correctly states.

JR

----- Original Message -----
From: "Olivier Cahen" <o_cahen@xxxxxxxxxxxxxxxx>
To: <photo-3d@xxxxxxxxxxx>
Sent: Sunday, October 08, 2000 2:45 AM
Subject: Re: [photo-3d] Digest Number 286. Mirrors


> Good mirrors for any optics should be in glass with a metal layer on
> the front face, but such mirrors are very difficult to find and very
> expensive.
> I do not recommend you to use a beamsplitter, there are many serious
> backdraws with beamsplitters. If the resolution of your camera is poor,
> such as most of the digital cameras (all except professional ones, more
> than US$5000), the resolution of your half images will be only half. You
> would get a huge keystone distortion, with no possibility for
> compensation, so that you can never see good images in projection. Only
> some types of beamsplitters, with mirrors in different planes making the
> image rotating by 90°, can avoid this distortion.
> Stereo images in two subsequent shots can be good...
>
>
> > Message: 10
> >    Date: Sat, 07 Oct 2000 20:00:50 +0200
> >    From: andre <dbvs@xxxxxxxxxxxx>
> > Subject: Mirror beam splitter device
> >
> > I am trying to build a device to take a 3D photo using a digital
camera - I
> > have seen samples of this used on camcorder where mirrors were used
placed
> > like a beamsplitter . I do however remember reading that a certain type
of
> > mirror is needed as not all mirrors will reflect each others image -
does
> > anybody know about this.
> >
> > For those interested I see that www.ddd.com has uploaded there new web
site
> > and it is pretty neat -
> >
> > All help would be appreciated
> >
> > Andre
>
>
>
>