P3D Re: it is a question of projection

[Oliver Dean <3d-image@xxxxxxxxxxxxxx>]

Lincoln Kamm wrote:
> So,.... I would like anyone that has owned some 3-D projectors to let
> me know what they have found to be the pros and cons as well as if
> there is some general opinion as to what are the best projectors to
> consider.  I don't think I am ready to jump into any of the ones that
> are over $500,  but feel free to talk me into it if it is worth it.

WARNING -- this is a LONG post!  It is revised from a private post I
made earlier to a private inquiry:

TDC made two models of projector, the 116 and the 716.  The 716 was
designed for 750 watt lamps maximum, whereas the 116 was designed for
500 watt lamps.
  
The 716 has a slightly better slide carrier than the 116, in that it is
a sturdy stainless steel carrier with a built-in shutter for obscuring
both slide windows during the slide change. However, the openings in the
carrier were designed for 5 perforation Realist format slides only; if
you want to project larger slides, the openings can be CAREFULLY filed
to a larger size so as to accommodate so-called 7 perforation European
format slides, but any larger opening would interfere with the proper
operation of the shutter assembly.

The 116 can be rewired to accommodate 750 watt lamps by simply using a
heavier gauge wire for the internal connections -- not a difficult chore
for someone handy with a soldering iron.  A test of the heat generated
at the power plug would be a good idea, however.  If the plug gets too
hot, it would be advisable to change the socket on the projector to a
heavier capacity, as well as the plug on the cord, or to wire the power
cord permanently into the projector (probably a better solution).  Of 
course, the blower fan must be in good operating condition!

The 116 has an aluminum carrier, which can be more easily damaged than
the stainless steel carrier of the later model 716.  In addition, a
spring loaded shutter mechanism is mounted in the projector and is
cammed into and out of position by a protrusion on the moving part of
the aluminum slide carrier; this triangular shaped protrusion makes
installation of the carrier a little tricky during set up and breakdown,
and users unfamiliar with the projector can cause the carrier assembly
to jam or even get bent or damaged if they are not careful. The
triangular protrusion can get a groove worn into it by constant contact
with the shutter mechanism, but this wear does not usually degrade
operation of the shutter unless the groove gets very deep.  On some
models I have seen, the triangular protrusion is reinforced with a split
aluminum tube slipped over the edge of the triangle that contacts the
shutter mechanism.  

However, the model 116 carrier has one tremendous advantage -- it has
openings large enough to accommodate up to full frame 35 mm stereo pairs
mounted in a single slide of the standard 1 5/8" height.  The carrier
also has a second channel for projecting slides 2 inches high, which
accommodates standard 2 x 2 monoscopic single slides, but,
unfortunately, will not support twin separate 2 x 2 slides for stereo
(the support spring at the top of the channel is only just long enough
to align one 2 x 2 slide -- a second slide in the channel will tip
forward or back at the top and cannot be focused).  This second channel
WILL accommodate twin 2 x 2 slides that have been fastened together with
an appropriate spacer to form a single slide, however.  It will also
accommodate the rare mounts that were made for full frame stereo pairs
and that were 2" high. 

Clearly, if full frame 35 mm stereo pairs are important to you, the
model 116, despite its older design, might be the better choice for
you.  Be sure that there IS an aluminum carrier in good condition(!)
with the projector, and that the built-in shutter is still in or with
the projector; some model 116's were outfitted with a removable adapter
to accept the better made and quieter stainless steel carrier, and a
former owner may have discarded the older aluminum carrier and shutter
mechanism.

If you decide on a TDC, whether a model 116 or 716, BE SURE THE LENSES
ARE
PROPERLY ALIGNED IN THE HOOD!  If they aren't, the repair can be
expensive,
requiring somebody to machine new threaded lens holders.  There were a
few projectors made without proper quality control of the lens holders,
and the
result was a projector that could not be focussed over the entire
picture
area of one or both images.  Check by unscrewing one of the lenses, if
necessary, until both lenses are even with each other.  Then. looking
down on them from above, lay a horizontal straight edge across the front
of both lens barrels.  If the straight edge touches both sides of both
barrels, then the lens holders pass the first test.  Now from the side
of the projector, sight along the top of one barrel and see if it is
parallel to the top of the other barrel; if so, the lens holders pass
the second test and are probably OK if the tests still check out after
you change the horizontal and vertical adjustment positions on the
projector a few times. If there is a discrepancy in either test, I would
recommend rejecting the projector unless you know somebody who can
machine one or two properly aligned lens holders inexpensively.

Compco (no longer in business, either) made two models, the "Triad" and
the "500".  In this case, the older "Triad" was the better projector of
the two, although the "500" (which I own) can be modified (at
considerable expense and trouble) to behave acceptably. Both projectors
were designed for 500 watt operation, and I have not tried to rewire
either
for higher wattage because the cooling fans, while commendably quieter
than the TDC fans, probably do not have the cooling capacity to handle
750 watt lamps. 

Compco slide carriers are sturdy but simple in design, and have the
disadvantage that, during a show, you must remove a previously projected
slide and replace it with the next one first on one side of the
projector, and then, after the slide carrier is pushed through to
project the slide you just loaded, you must remove the old slide and
replace it on the other side of the projector.  Unlike the TDC, you can
go slightly buggy ping-ponging back and forth from one side of the
projector to the other during a rapidly paced show, but you get used to
it after a while.

It has been a long time since I operated a Triad (our Pasadena Stereo
Club Triad, with special Simpson F1.4 - I think - lenses, was stolen
about fifteen years ago).  But my recollection was that the carrier is a
simple frame that would accommodate slides mounted in any 1 5/8" x 4"
mount, which would allow it to project slides mounted in any stereo wide
format masks. Be sure to check this if you are looking at a Triad,
though!   But there is no built-in shutter, and the slide change
movement is annoyingly visible on screen. The projector was as solidly
made as the TDC and had two advantages:

1.  The focusing knob is at the back of the projector and is easily
accessible to the operator, unlike the TDC.  And horizontal/vertical
adjustment, to align the two images on screen with respect to each
other, is done by a single knob on the side of the projector, which is
also more easily accessible than the TDC knobs.

2.  The polarizers are located between the slide carrier and the lenses,
unlike the TDC, where the polarizers are located between the lamps and
the slide carrier for additional heat absorption.  Although the Compco
arrangement requires a better grade of polarizer that is optically flat
so as not to degrade projected image quality, the location after the
film in the light path insures that maximum polarization is achieved. 
In the TDC arrangement, some films can actually degrade the polarization
and cause excessive "ghosting" (unwanted "cross talk" between the left
and right images when viewed through the polaroid glasses).  But in the
Compco projectors, polarization takes place only AFTER the light has
passed through the film, so that any degradation that may be caused by
the film is eliminated.  However, because of the absence of polarizers
behind the film. the slides can heat up a bit if left in the projector
too long.  Since most good slide shows never leave a slide on screen for
longer than 15 or 20 seconds at most, this should not be a problem.

The Compco 500 was an attempt to make a more compact, lighter, more
modern design, but the engineering was unsatisfactory.  The slide
carrier is similar to the Triad's but with stainless steel aperture
openings that would have to be filed or machined out to accommodate wide
format slides (because there is no shutter, this can be done much more
easily than enlarging the openings on a TDC carrier).  

The 500 projector includes built in switches, triggered by the slide
carrier movement, that switch the lamps off during a slide change and
switch them on again when the change is complete.  This is a much less
satisfactory arrangement than the mechanical shutters of the TDC,
because the part of the slide movement during a change would be visible
until the moving carrier turned the lamps off. In addition, the switches
were so stiff on the unit I bought that the carrier would not operate
unless the projector were bolted down to a heavy table, and even then
the carrier operation would be unacceptably difficult.  Rather than
trying to find less stiff switches, I simply took them out, designed an
adapter for a TDC stainless steel carrier, and used an extra TDC carrier
I was able to buy at the time.  I enlarged the openings in the TDC
carrier so that my modified 500 will now show wide format stereo slides
up to European (7 perforation) format.  This would be a difficult change
to make today, because separate TDC stainless steel carriers for sale
are rare. 

Location of the polarizers is similar to the Triad, an advantage, in my
opinion.  Also, the ease of vertical and horizontal on-screen stereo
adjustments is similar to the Triad's, also an advantage.  

The big disadvantage of the 500 is the poor design of the focusing
mechanism. For a number of reasons, there is slack between the focusing
knob (conveniently located on the side of the projector) and the hood
that moves the lenses, which makes it nearly impossible to do a quick,
positive change in focus.  Also, the tracks intended to keep the hood
aligned are poorly designed, allowing the hood to skew slightly to one
side or the other during focusing, which can throw one lens slightly out
of focus with respect to the other.  I was able to correct some of the
slack but not all of it, and the poor tracking was helped some by
careful lubrication of the tracks, but it is still not as precise a
focusing mechanism as it should be.

One other thing I did with my 500 was to paint the inside of the hood
and the surface it rides on a flat black, which noticeably improves the
contrast of the projected images.  And, of course, I replaced the
polarizers with new ones.

If you are interested ONLY in twin 35 mm 2 x 2 stereo, you might
consider a twin Kodak Carousel Ektagraphic rig. This is quieter, uses
less power, creates less heat, is a more modern technology, permits
automatic operation, can work with cheaper slide mounts, and can be
programmed to work with slide changing signals on an audio taped sound
track.  Susan and David of Reel 3-D Enterprises
<http://www.stereoscopy.com/reel3d/>, among others, are a good source of
information about this method of projection, and they can also supply
most of the accessories you would need to add to a pair of Ektagraphics
for
convenient stereo projection of twin 2 x 2's.

Hope this helps -- let me know what you decide to do.

Cordially,
Oliver Dean