Wednesday, July 15, 2020

LEITZ PRADOLUX RT-300, A GEM OF THE PAST





By Heinz Richter

In the late 70s to early 80s, the division of Leitz in the US had several ventures of their own, items actually made in the US, like the Tiltall tripods.  One of those items was the Leitz Pradolux RT-300, a slide projector designed and made in the US.

While slide projectors for the most part are a thing of the past, the RT-300 deserves mention because it was very unique in its own right.  It was the one and only projector in the Leitz lineup that used the Kodak style round tray.  But it most certainly was not a “me too” approach to the most popular tray type in the US.  While in principle similar to the Kodak and other round tray type projectors, the RT-300 had several features not found elsewhere.

The most unique one was the illumination system.  Heat, transferred from the projector bulb to the slide has always been a problem.  To protect slides from heat, virtually all projectors utilize a heat absorbing glass.  While these work quite well, they also do add a slight green cast to the colors.


Not so the RT-300.  The light bulb was positioned in a 90˚ angle to the light path.  The light was reflected by a dichroic mirror with a coating that reflects the visible spectrum of the light, but not infrared and heat.   The result was brilliant illumination since only the correct color temperature passed through the optical system.  This allowed for a gate temperature of a modest 155F.

Another welcome feature was that the slides were preheated to avoid any popping during projection.

Some of the warm air from the cooling system was diverted
to prewarm the slides

Another welcome feature was the very accurate slide registration.  When a slide dropped into the gate, two levers gently but firmly positioned it.  One pushed the slide against a retainer in the focal plane, and the other registered the slide horizontally.  That assured easy set up for multi projector use and multi-screen use.


The Pradolux RT-300 accepted all of the unsurpassed Leitz projector lenses, including the curved field lenses which gave substantially better edge to edge sharpness with non-glass mounted slides.

While the projector would accept any Kodak type round tray and accessories like stack loaders, the tray supplied with the RT-300 was made by Kodak of West Germany with a transparent plastic cover to keep slides dust free and a corrosion resistant base plate, and cutaway slide separators for easy editing.


One very welcome feature was the very easy lamp change.  No need to move the projector to get to the lamp.  All that was necessary was to open the lamp housing door and pop the lamp out with the ejection lever.


Other welcome features were a coin-slotted screw on top of the projector to tray removal regardless of the tray position.  A hi-lo switch and special circuitry to extend lamp life, built-in cord reel and retractable cable, thumbwheel for accurate leveling, continuously adjustable interval time from 2 to 20 seconds.


 

As each RT-300 reached the end of the production line it was cycled through 450 slides over a 20 minute period. It was then checked and tuned by the production department with a special set of slides to verify all aspects of performance.  Every projector that passed went to quality control where it was again put through its paces.  Samples were taken from the line daily and run seven hours continuously under varying conditions.  Regularly units were put through 50 hour and 2000 hour non-stop tests.

This rigorous quality control was further assurance that the RT-300 equaled the dependability and performance that made Leitz the premier name in quality slide projection.

The overall quality and reputation of Leitz slide projectors must have been one of the reasons why the Science Museum of Minnesota selected the RT-300 as their multi projector system in the Omni Teater before switching much later to digital projectors.




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