thats almost as bad as knowing job control language for an IBM AS/360 Mainframe. :) Also, working on reel to reel tape machines. Its really too bad that most people these days don't remember the technology that was the predecessor to the current media. You ask a kid today what a floppy disk is and they might look at you like a deer caught in the headlights. Or how about coders these days that couldn't conceive of a program written in basic and having to work tightly in only 8k of ram. Pretty soon, I imagine, keyboards are going to be quaint reminders of an old computing past.

DE n7zzt Eric

On Nov 3, 2015, at 8:11 PM, Tom Fowle wrote:

> 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...