klub stereoskopické fotografie

Dual monitor set-up for stereoscopic viewing

Matěj Boháč

česká verze

For the time being (written in 2010) there is no digital stereoscopic viewing method that would at least approach the experience of viewing a stereo slide in a quality back-lit viewer (my prefered technology so far). To get seriously started in digital stereoscopic imaging (both photography and computer generated graphics) I have decided to build a dual monitor - single mirror set-up which brings me as close to a slide in a viewer as one can get (but certainly not to the same level!). This viewing method has been popularized for years by the stereoscopic guru, professor John Hart of Colorado. I would like to thank John for sharing his experiences and for supporting me with my own project. See also John's web-page describing his solution.

dual monitor - top view

Top view of the set-up. Parallel view - click to see the same as crossed view

The idea is simple - Both eyes seem to be looking straight at the front monitor where one image of the stereo pair is displayed, but the view of one eye (left in this case) is reflected by a mirror sideways, to the other monitor with the other half of the stereo pair - which is horizontally flipped.

dual monitor - drawing

As long as the angle between the monitors is twice the angle of the mirror, the geometry is correct and the image is undistorted. If properly adjusted, the image of the reflected screen exactly overlaps with the "front" screen from any point of view.

dual monitor - front

A dual head graphics card is used to connect both monitors to the same computer.

The advantages of this set-up, compared to other digital viewing methods:

  • very high resolution
  • no ghosting, full colour
  • fixed viewing position, which may be considered a disadvantage by many, but provides orthoscopic viewing

disadvantages: very bulky, can not be carried around like the Realist Red Button slide viewer;-)

Two quality CRT monitors can be obtained quite easily nowadays as many offices are switching to LCDs. I got mine for free. The only remarkable investment is the required high quality front surface mirror (an ordinary mirror causes multiple reflections). The mirror I used (12" x 16") is larger than necessary, for my 18" (exactly 456mm diagonal) monitors, the minimal dimensions of the mirror would be about 260mm x 200mm (WxH).

my design requirements:

  • permanent set-up, allowing me to switch to stereo with a single movement without any further adjustments
  • ergonomic solution, allowing me to use one of the monitors for ordinary (mono) work as well as to comfortably view stereo for hours
  • Otrhoscopic viewing - geometry providing a natural viewing angle, derived from the characteristics of 35mm slide viewers.

Having this in mind, I have firmly fixed the monitors together. The mirror is on a hinged plate, which may be swung between the mono- and stereo- positions. The whole set-up is tilted, allowing for a natural and ergonomic use.

All parts used are symmetrical, so the whole setup can be easily changed to "mirror-right" arrangement.

dual monitor - swinging mirror

Animation showing the two mirror positions. Parallel view - click to see the same as crossed view

dual monitor - side view

Side view of the set-up, showing the sloping-down arrangement. Parallel view - click to see the same as crossed view

This may give you a basic idea how I constructed my set-up. I am sure that many things can be done better and more effectively in a properly equipped workshop, which I don't possess.

The first challenge was to find means of firmly but not permanently mounting the monitors together. I have opened the monitor cases and used M3 bolts to attach small steel plates with tapped M5 threads to the metal structure of the monitors (two at the top and two at the bottom of each monitor). The screen has been wrapped in cardboard during the process to avoid damage.

Click on the images to display a larger version

dual monitor - threaded steel plates dual monitor - threaded steel plates

Once equipped with metric threads, the monitors can be attached together using metal plates (2mm steel sheet).

dual monitor - threaded steel plates

The front surface mirror I used is less than 2mm thick. Therefore I needed a perfectly planar and rigid support, yet thin and not too heavy. I have used a sheet of 2mm duralumin, strengthened by aluminium L-bars. The purpose of the crossed bars is to avoid twist. Attached usind 3mm aluminium rivets.

dual monitor - mirror

Front view

dual monitor - mirror

Back view

dual monitor - detail

Top-front corner of the plate, showing the front vertical edge, formed by the duralumin sheet bent to 90 deg. and rounded (hiding the sharp edge of the mirror), and the strengthening aluminium L bar attached at the top.

dual monitor - detail

Detail of the hinge

dual monitor - detail dual monitor - detail

Fine adjustment of the mirror position - top (M4 nuts) and bottom (L - bracket fixed by an M5 screw)

dual monitor - detail

A piece of clear plastic used to protect the mirror from breath.

While the "front" monitor is tilted up in an ordinary manner, the "mirrored" monitor has to be tilted both up and sideways, which the original monitor stand does not permit. A wedge-shaped block of wood is used as a stand. Determining the dimensions of the block was a complicated geometrical exercise, I carefully measured the monitors and built a 3D CAD model of the whole set-up for this purpose. The following images show the process of etching the wooden block, which was a bit more interesting work.

dual monitor - wooden wedge plates dual monitor - wooden wedge plates dual monitor - wooden wedge plates

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