The Stereo Realist Model 82 Projector

Summary

The Stereo Realist projector was clearly an attempt by the David White Company to design the ultimate in stereo projectors. It posesses many novel design features, and was intended solely for use with glass mounted stereo slides to ensure maximum precision. However in many areas the design is over-complicated, and this has lead to unreliable performance. The slide gate and focussing system appear to only be practical when using glass mounted slides.

 

Introduction

Stereo Realist projectors are quite rare, probably because they were expensive when originally produced. The cheapest Model 81 was priced at about US$450, at a time when the Realist camera was US$160, and the TDC stereo projector was just US$170. Since the opportunity arose to examine a Model 82 Stereo Realist projector, it was decided to summarise some aspects of the projector on this web page, as most people don't get the opportunity to see one of these.

Illumination System

The Model 82 can be equipped with a pair of lamps that may be 500W, 750W, or 1000W each. The lamp voltage is of course 110V since the projector was designed for use in the USA. (Apparently the cheaper Model 81 projector can only be equipped with two 500W lamps).

Condensor System

The condensor system is conventional (see also the associated article on projection optics at this site). A larger mirror behind each lamp reflects light emitted from the rear of the lamp back through the spaces between filament coils. The mirrors can be adjusted by hand to align them with the rest of the optical system (this is a pre-set adjustment, and not one intended to be done by the owner).

The horizontal lamp position can be adjusted by the owner using controls on either side of the projector body, which move the lamp sideways when turned. Lamp height and fore/aft position is pre-determined by design and not adjustable.

The first condensor is approximately 50mm in diameter, as is the heat filter, second condensor, and polariser. The focal length of the first condensor is about average for a projector of this age, but is longer than that of the first condensor found in the TDC projector. As a result, the distance from the lamp filament to the first condensor is larger than desirable, so the light-collecting ability of the condensor system appears to be less than can be obtained with other designs (eg: TDC, or modern aspherical first condensor).

The complete condensor assembly is mounted in a removable carrier which makes dis-assembly and cleaning a breeze. This and other design apsects of the Realist projector give the impression that this was a "no-holds-barred" design excercise for the Engineers at the David White Company.

Polarising Filter

The polarising filter is sandwiched between glass and mounted in a round bezel, which is in turn is mounted on the condensor system removable carrier. The aligment of the polariser may be adjusted by the owner if required, to minimise ghosting in the projected stereo image.

As the plastic polarising filter is mounted between glass it is likely that it will get warmer than a filter held in free-air. Cool air is circulated past the filter, although less than that in the TDC projector (which has a torrent of air).

In the unit examined the polarising plastic had buckled between the glass sandwich, which is evidence of higher than desirable temperatures.

 

Slide Gate

If there is one element of this projector that makes it different, it is the design of the slide gate and lamp-dowsing system. In a properly working Realist projector the slide gate is a magnicent piece of engineering. However the mechansism is very complicated and is easily prone to operating less than perfectly.

The slide is carried in a rotary carrier that can hold two slides - one in each half. The slide in the bottom half is the one being projected on the screen, while the slide in the top half is the one being removed and replaced by the next slide to be projected. One advantage of this system is that the slides go into the gate in exactly the same orientation as the the hand viewer - so theoretically there should be fewer slides projected upsidedown from mistakes in orientation.

The rotary carrier has stiff spring-clips for holding the slide in position while the gate is rotated quickly into position. These spring clips are so stiff that they deform the shape of cardboard stereo mounts put into the carrier. However - on reading the instruction manual, it is made quite clear by Realist that the projector is:

designed only for the use of glass mounted slides - never put cardboard mounted slides into your Realist projector.

 

The slide carrier can be removed from the projector chassis by pushing a button on the carrier and pulling the carrier upwards. The manual suggests that carriers for other formats would become available, but this may never have happened.

The central bearing of the slide carrier might have been a crucial element in getting accurate, repetitive slide position in the gate. However this is not the case. The central bearing is quite slack, and instead the carrier is located firmly in position by two metal arms that contact the bottom of the gate in its rest position. These arms retract when the carrier is rotated, and as the rotation nears 180 degrees the arms spring back upwards to lock the carrier into position. This appeared to work satisfactorlity on the unit examined.

The action of rotating the slide carrier is initiated by pushing a large lever at the back of the projector all the way to the bottom (this has a throw of about 250mm). When this lever is pushed the following actions take place:

As you can see, designing a mechanism that converts the downward motion of the actuating lever into the many actions required to rotate the gate is a complex design challange. In addition the gate has provision for adjusting the vertical alignement of the left and right images (see next section). It is claimed by some owners that the slide gate mechanism can be unreliable.

 

Projection Lens and Alignment Controls

The projection lenses are 3.5 inches focal length, f2.3 aperture, and feature 5 elements. The two lenses are mounted in a magnificent sub-assembly which has two controls on it - one for adjusting the lens spacing, and one for adjusting the focus of both lenses through a rack and pinion system. The short focal length of the projection lenses makes the image larger for a given projection throw, however a disadvantage is that the focus is more sensitive to slide curl or popping (which is avoided through the use of the recommended glass mounts.)

Individual focus of the right-side lens is possible, however during operation the lenses are recessed inside the front face of the projector making it almost impossible to turn the barrel of the right-side lens without obstructing light from the projector. In addition the thread is very fine, and the lens barrel is hard to grip, making individual adjustment very slow. This is another sign that the projector was intended stricly for use with glass mounted slides.

The vertical alignment of the left and right images is not done by moving the lenses - but instead by slightly rotating the slide gate. This is another complication in the design of the slide gate, although it is an innovative approach to the problem. The two arms that hold the gate in position can be rotated slightly by a knob beside the slide gate, and this in turn shifts one side of the slide slight up, and the other side down (although at the same time some small rotation of the image is also seen on-screen).

 

Cooling

The fan intake is at the front of the projector, and the fan appears to be a hybrid of the axial flow / centrifigul blower type. The fan motor is not an induction motor as found on most projectors, but instead a DC motor with brushes, that can also be operated on AC (much like an electric drill motor). The fan speed can be set to high for operation with 750W or 1000W lamps, or to low when using 500W lamps. Due to the very high speed of the fan, the noise level is very high - almost to the point of being intolerable on high speed.

 

Overall Construction

The two ends of the projector are made from large casting, with fins extending from top to bottom. These two castings are joined by various sheet metal sections that form the side casing of the projector. There is a large slot in the middle of the projector for the slide carrier. In the unit examined, this seemed to introduce a point of mechanical weakness in the construction, however this particular projector has been dis-assembled many times, and a number of scews were stripped, which would not normally be the case.

The projector looks magnificent, being finished in high-gloss enamel. The unusual design is also an very eye-catching. The projector comes with an integral case, that it can remain secured to during use.

 


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