Knowing how things work, or used to work is never useless.
At the least it's interesting.

Used to run 16 MM projectors in highschool in the 60s, but don't remember
the filter. Maybe those school units didn't have the freeze frame.
thanks for the fun
tom Fowle WA6IVG

On Tue, Nov 03, 2015 at 02:22:44PM -0600, Martin McCormick wrote:
> 	A lot of what is left of my brain is useless knowledge by
> today's standards. When I worked as a technician with the OSU
> Audio Visual Center in the eighties, I repaired 16-millimeter
> film projectors among many other things and I have a whole
> treasure trove of trivia in my head that doesn't get you very far
> today.
> 
> 	Did you know, for instance, that if the film stops moving
> for even a fraction of a second that the heat from the projection
> lamp is sufficient to melt it? Most projectors had a freeze-frame
> function but it only worked because a special piece that greatly
> reduced the amount of heat/light was supposed to drop down
> between the film gate and the film, itself.
> 
> 	We had a few machines that came in because a mechanical
> part that held the filter piece up and out of the way failed and
> the piece would slowly swing down and cause the light output to
> appear to go very dim.
> 
> 	How does a person who is blind work on a film projector?
> Most of the mechanical failures that befall 16-millimeter
> projectors cause audible issues also.
> 
> 	Sound film projectors must yank the film through the gate
> in a series of 24 very fast jerks per second so that each frame
> of the picture is still for 1/24 of a second. When the film
> reaches the sound pickup, it must not have any trace of the jerky
> motion and moves as smoothly as audio tape. There are failure
> modes that cause the film to move more smoothly than it should
> through the film gate and other failures that make it move in a
> jerky manner through the sound pickup. Those usually make the
> machine clatter with an extra loud sound or the sound has a
> terrible flutter in the speed which is unacceptable. It is
> necessary to examine the film transport to diagnose the problem
> and fix the broken parts.
> 
> 	There is a Walt Disney movie which I think might be
> "Bambee" in which there is a scene where animals are talking to
> each other while under water. Their voices all sound fluttery
> like someone with water in their throat. One time, my wife and I
> watched this film because she wanted to see it again after many
> years and I had never watched it at all. I almost fell out of my
> chair when that scene came on. Some technician simply blocked the
> rotation of the sound drum and fed that audio in to the movie as
> a special effect. I thought it was brilliant and never imagined
> that someone would actually want that sound to appear, but it was
> perfect for the scene.
> 
> 	I remember running across many weird problems that were
> usually the fault of wear and tear on belts, gears and clutches.
> That's where I accumulated all this useless knowledge.
> 
> 	So, what makes the film stop and melt? Ripped out sprocket
> holes along the edge. That will turn torn-up film in to torn-up
> melted film. If this had been back in the really old days, the
> film which used to be made of celluloid would have burst in to
> flame and started a real fire.
> 
> Martin
> 
> Colin McDonald <[log in to unmask]> writes:
> > ah, I love teachable moments!!!
> > They call me a walking encyclopedia of mostly interesting, but useless
> > facts...