New Projector Throws Illustrations Behind Speaker’s Back (Apr, 1935)
New Projector Throws Illustrations Behind Speaker’s Back
FACING the audience as he talks, a speaker may now illustrate his lectures on a screen behind him without turning around with the aid of a novel optical projector recently perfected by a well known German firm.
The speaker, directly facing his audience, illustrates his talk by writing or drawing horizontally on a sheet of cellophane lying on a glass table before him, and the script is projected, ten to fourteen times enlarged, on the wall screen behind him.
Underneath the glass table, the light of a 500-watt bulb is condensed and reflected through the transparent cellophane. The lines then pass through a lens to the mirror and -are projected onto the screen.
good one !
Comment by iswandoyo — August 9, 2007 @ 1:51 am
I was once told that the over-head projector was invented by the military so that instructors could keep an eye on sleepy GI’s.
Comment by Timmay — August 18, 2010 @ 5:10 pm
You were told wrong.
1939 Principle used in bowling alleys http://www.google.com/patents?.....38;f=false
1941 same inventor http://www.google.com/patents?.....38;f=false
1944 civilian http://www.google.com/patents?.....038;pg=PA1
1948 (filed) civilian http://www.google.com/patents?.....38;f=false
1948 another civilian http://www.google.com/patents?.....38;f=false
1963 The one we all grew up with http://www.google.com/patents?.....38;f=false
Comment by Firebrand38 — August 18, 2010 @ 5:56 pm
Very informative, thank you.
And yes I do remember the last one quite well. Right down to the trapezoid door to access the bulb.
Comment by Timmay — August 19, 2010 @ 8:06 am
Wow 500Watt bulb. Must have cost a fortune back then to keep that thing going.
Comment by M.S.W. — August 20, 2010 @ 8:05 am