Comparison of TDC 116 and TDC 716

[P3D KENNETH LUKER <KLUKER@xxxxxxxxxxxxxxxxxxxxxxx>]

My neighbor has a TDC 716 for sale, and I borrowed it to show a 3-D 
program at my library documenting the two-year project that doubled 
the library's size.  I was interested in comparing the projection 
with that of my TDC 116.

His 716 has four-inch lenses compared with my 116's five-inch lenses, 
but it has 750 watt lamps compared with my 500 watt lamps.  The 
projected image was larger with the short lenses, of course, but the 
brightness seemed to be about the same.  For a large-group 
presentation, I preferred the larger image, and I couldn't back my 
116 up far enough to fill the larger screen.

Later, at home, I put the two projectors side by side for a direct 
comparison.  At home I can fill a 50x50 screen with the 116's five-
inch lenses, but I still have to peer from back at the projector to 
focus the image.  Also, the noise of either projector fan is loud 
enough that the viewers at home have a hard time hearing any 
commentary I make from the projector, and I can't hear any of their 
comments or questions.  For that reason, the shorter lenses might be 
better at home, so I could interact with the audience better.  The 
comments of my family are rather predictable though, and I don't need 
to hear them clearly in order to respond.

Since the brightness of the two projectors seemed about the same (I 
was surprised that the 716 wasn't spectacularly brighter) I measured 
the light intensity at the screen using my incident-light exposure 
meter.  First I projected onto the screen with no slide in the 
carrier and both lamps of one projector turned on.  I set the meter 
to indicate exposure value.  With the projectors at identical 
distance from the screen (about twenty feet, I think), the exposure 
value indicated for the 116 was 6.7, while that for the 716 was 5.6.  
The reduced intensity of the brighter lamps seems to be due to the 
greater dispersion of the projected beam by the shorter lenses.  I 
repeated the experiment several times and got consistent results.

I also put a slide into the carrier, showing an interior shot which 
contained a bright exterior window.  The window showed almost white 
and was a fairly large area, certainly the brightest spot on the 
slide.  With that same slide in each projector sequentially, I 
measured the intensity of light at the screen at the center of the 
window image.  The 116 showed an intensity of 6.2 and the 716 had in 
intensity of 4.7 or 4.8.  My subjective impression of the relative 
brightness when observed from the projector was that the 116 was ever-
so-slightly brighter than the 716.  In practice, I believe there may 
be not enough difference to be bothersome.  Of course, the image from 
the 716 was considerably larger, and the total light on the screen 
was therefore greater with the 716.  Either projector would be 
entirely satisfactory for home use.  

Finally, I removed one of the 500 watt bulbs from the 116 and 
inserted one of the 750 watt bulbs from the 716 into the 116.  The 
bases were of the same type, although the 750 watt bulb was mounted 
with a porcelain separator between the bulb and the base.  The 
diameter of the 750 watt bulb was also slightly greater, although the 
center of the filament was the same distance from the base in each 
bulb.  The larger diameter of the 750 watt bulb caused the bulb to 
touch the metal shroud in the 116 projector at one place.  I noticed 
that the socket was slightly off center, and I could have 
disassembled the projector to correct its placement but decided not 
to do it just for the experiment.  Had the socket been centered, the 
bulb would have had almost one quarter-inch clearance on all sides--
that seemed enough to allow the air to pass all around it.  George 
Themelis says that his 116 has 750 watt bulbs that work fine.  I 
didn't fire the beast up, lest the portion touching the shield should 
cause the lamp to fail.  (After all, it wasn't my lamp!)

The 116 projector has a circular shroud completely around each bulb, 
with just an opening cut in front and back to allow light reflection 
from the mirror, and projection through the condensers.  The 716 has 
a square shroud around each bulb, with the front face missing and a 
hole cut in the back to allow reflection from the mirror.  The space 
around the bulb is significantly larger in the 716, and as has been 
pointed out by George, the 716 has porcelain sockets, while the 116 
has bakelite sockets.  The embossed stamping on the socket's 
bayonet portion, made of metal in both versions, says "1000 W."

My conclusion:  The larger but dimmer image of the 716 is not 
sufficiently better than the slightly brighter, smaller image of my 
116 to motivate me to change projectors.  The five-inch lenses fill 
up my 50x50 screen, so I don't really need a larger image at home.
If I fix the centering of the socket, I may yet get 750 watt bulbs 
for a really bright image with the long lenses. 

Ken Luker_______________________________________________________________

Kenneth Luker, Assistant Director
Systems and Technical Services
Marriott Library
University of Utah
Salt Lake City, Utah
KLUKER@xxxxxxxxxxxxxxxxxxxxxxx


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