Teleprompter 101: How the prompter works
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A Teleprompter system is composed of basically 2 elements.

1. A computer: used to edit, scroll and output the script.
2. A video monitor:
used to display the script.
 

The video monitor works just like an ordinary TV, with the exception that it displays the mirror image of the text. The monitor is adjusted (usually by the manufacturer) to display the video flipped horizontally. The text is not only written backwards, but the letters are backwards too.
The image below shows what the text looks like before the on-camera speaker see it. In this case the monitor is upside-down also.



prompter reversed - copyright 2006 by Greg Rice

A+ Prompter

A piece of tinted glass is then put over the prompter monitor at a 45 degree angle so that it reflects the image on the monitor. This allows the speaker to see the words as usual. The image below shows the prompter as the speaker see it.

copyright 2006 by Greg Rice
A+ Prompter

 

The picture below shows a typical set-up for a camera mounted teleprompter.

1. Camera
2. Shroud: holds glass
3. Prompter Monitor: facing up
4. Tinted Glass

Teleprompter_schematic designed by Greg Rice

 
The Secret

How does camera see through the glass without also "seeing" the reflected the words?

Well, the secret is that the back side of the glass is enclosed in a black shroud. Consequently the glass acts like a one way mirror. If you've ever seen an interrogation scene on a TV police show, you'll notice that there is always a mirror in the room with the suspect. The "mirror" is really just a piece of tinted glass and the room on the other side of the glass is always kept dark where the other detectives watch the interrogation. Consequently, the suspect on the lighted side can't see into the dark room on the other side. And since the glass is tinted it reflects all the light from the lighted room and looks like a mirror.

You may have seen the same effect on tall office buildings with tinted windows. During the day, when it's bright outside, the windows look like mirrors, they just reflect the sky. But at night when it's dark outside, you can see the interior of the office building.

So on the teleprompter, the camera lens is "looking" through the dark side and doesn't see any reflections. But the talent is looking from the bright side and sees the words on the prompter.

 

copyright 2006 by Greg Rice

If you look very carefully at this picture you can see the bottom of the camera lens. It's just below the words "one place" and just above the word "golf".

 

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