Digital Image Projection

Practically all of my stereo photography now involves an Van Ekeren P43 Twin Rig while my vintage Realist-format cameras remain safely stored away. Most of my images end up as Holmes stereoviews which, whether set up in black and white, sepia, or full-color, look fantastic with a good viewer. Unfortunately, the opportunities to show my pictures off are limited, especially in a group. That got me to thinking about stereo projection - something I hadn't done for about 40 years. Today there are three distinct possibilities - active digital projection, passive digital projection, and passive slide projection. Here is a summary of the hardware requirements for each:

	Active Digital >$4500	Passive Digital >$2200	Passive Slides >$750
PROJECTOR	1 - 120Hz DLP ($3600)	2 - SVGA DLP ($2000)	1 - Realist Format ($500)*
GLASSES (10 pairs)	Wireless LCD Shutter ($900)	Passive Polaroid ($30)	Passive Polaroid ($30)
SCREEN	Any ($?)	Metalized ($?)	Metalized ($?)
COMPUTER	Laptop ($?)	Laptop	----
SLIDE MOUNTING SUPPLIES	---	---	$200

This is currently the state-of-the-art and requires a DLP projector with a high refresh rate (120 Hz) to avoid flicker, since the effective frame rate drops to half the refresh rate of the projector. Such projectors are currently expensive, with the added expense of wireless shutter glasses. If you could tap the same source used for the movie theater glasses, you might save something here. Standard screens can be used and a laptop or other computer is required to drive the projector.

The DepthQ projector from InFocus is one of the few projectors with a refresh rate (120Hz) that is fast enough to avoid objectionable flicker. The photo also shows the wireless shutter glasses and the IR emitter that controls the glasses in the audience.

This technique uses a pair of DLP projectors, but they do not have to have a particularly fast refresh rate. Each projector has a polarizing filter and inexpensive passive glasses can be employed. The approach does require a metalized screen and the laptop of other computer must have a dual-head video card to span the stereo pair across the two projectors. There are external hardware units ($150) that will do this with a standard video card if the driving computer is fast enough. Not included in the table above is a stand/holder for the two projectors so they can be aligned with precision. An alternative approach would be the use of a single fast-refresh projector with an active Z-screen polarizer, but that would be a lot more expensive.

A pair of DLP projectors in an adjustable stand with external polarizing filters. The particular unit is marketed by Studio3D. The stand permits adjustment in three axes of the upper projector to properly set the stereo window. This stand and filter system is extremely economical compared to equivalent units from other sources.

It can be a vintage model, like the TDC116 shown on the left (A), a modern RBT101 shown on the right (B), or a pair of standard slide projectors with an alignment stand and external polarizers. A metalized screen is required, along with passive Polaroid glasses. Since no computer is required, the set-up is quite simple and uncluttered. The budget above assumes a reasonable deal on a vintage TDC projector. Projecting slides with vintage equipment is the least-expensive of the readily available methods. However, there is no such thing as a free lunch, and you will spend more money converting your digital files to slides, since those TDC projectors have no way of showing them directly.

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