No Subject

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

Doc Lee wrote:
> Recently I have seen the TDC 30 slide "automatic changer" up for
> bid on eBay. Could you comment on this mechanism.
> Regards, doclee@xxxxxxxxxxxx 

Hi, Dr. Lee!

I had just been thinking that I had neglected to write about this device
earlier, when along you come and ask about it!  Thanks for asking!

The "automatic changer" you refer to was called a "Stereo Selectron
Changer," and although TDC called it "automatic," the only automatic
feature was that it fed the slide to be projected directly from a
special slotted storage tray and fed the ejected slide back into the
tray.  Operation was still manual -- you had to operate the slide
changer by hand.  You operated it by sliding a lever away from the
projector to the right to eject the old slide into the tray, and would
slide it to the left toward the projector to insert the next slide.  The
mechanism automatically advanced the tray one slide slot at the end of
the eject move.  You could remove the tray at the end of an eject move,
while the black out shutter was closed and the mechanism was free of the
tray slots. 

The black-out shutter was contained in the stainless steel carrier, but
was tricky to operate -- you had to push solidly on the operating lever
all the way to the end of its travel in order to get the shutter to
open, because the mechanism to open the shutter was levered open only in
the last fraction of an inch of travel and was somewhat stiff. 

The ones I have seen and used were below par for TDC (later bought by
Bell and Howell).  The design supported the slide tray on a long track
that was attached to the projector only at the center of the track.  As
a result, when a heavy tray of glass mounted slides was positioned near
the beginning or end of its travel, the track would twist and cause the
slides to misalign with the opening to the carrier behind the projector
lenses.  This would, of course, cause the mechanism to jam. I suppose it
would be possible to add a jury-rigged support that would keep the track
from twisting, but I'm not sure that it would be worth the effort,
considering the other disadvantages. 

Also, the stainless steel carrier containing the shutter mechanism was
not as sturdy as the regular manual stainless steel carrier, and it
could be bent or broken open with minimal stress. 

Finally, the Selectron was useless without the special "Selectrays",
which are hard to find.  Once in a blue moon someone comes up with some
for sale.  If you must have one to futz with, be sure that it comes with
at least a few Selectrays. Each tray holds only 30 slides, and if you
are going to want to put on a show with up to 150 slides, you would need
5 trays.

All in all, I found it to be a clunky, frustrating device that didn't
work at all smoothly and caused more problems than it solved.
I hate to say this, but I think manual operation from two long, home
made slotless trays on inclines on either side of the projector, one
tray to supply as yet unprojected slides and one tray to receive the
ejects, is a far smoother and much less frustrating way to put on a show
than trying to get a Selectron to work.

Good luck on tackling the job of making a slide carrier!  That is a
tricky job, especially designing a black-out shutter to hide the slide
movements during the change.  And making the openings large enough to
handle European and other wide formats complicates the shutter problem. 
Let us know how you do.   

Cordially,
Oliver Dean