|MadSci Network: Physics|
Nick, Unfortunately, not even lenses and mirrors can make this magic work! :-) I don't believe that what you are describing can be done. The reason is not so much an issue of the physics of projection as it is the amount of light energy generated by a TV. TV's work by exciting a phosphor on the back side of the screen with an electron beam. Electron beams were known as "cathode rays" - hence the name Cathode Ray Tube or CRT for a TV or monitor. The excited phosphor glows for a short time when excited by the electrons, giving off a small amount of emitted light as photons. These photons are focused by the lense in your eye and impinge on your retina, which sends a signal to your brain - and you get to watch "Friends". Unfortunately, as light gets farther from its source, it gets weaker, because the light is emitted in all directions and so at larger distances from the source, there are fewer photons to impact per unit area. In order to project light onto a surface at some distance and have it viewable, the light needs to be very strong. That is why overhead projectors and Liquid Crystal projectors have such powerful light sources behind them. They also collimate the light (make all of the photons travel in the same direction) very near the bulb, so that most of the energy is used in the projection and not wasted. The light coming from a conventional TV screen is much too weak and omnidirectional (i.e., is not collimated - goes off in all directions) to be useful for projection at any reasonable distance (e.g., greater than a few millimeters), regardless of lenses and mirrors. The least expensive method I know of is using one of the LCD type projectors that you can lay on top of a standard overhead projector. These aren't cheap, but they may get you what you need. Good luck with your project. [note added by MadSci Admin: There actually exist projection systems which use 3 CRTs, each one made so that it is capable of generating much more light than a standard TV screen. Each CRT has only one color of phosphor on it, which is one reason why it can generate more light than a standard TV (no space wasted on the inside surface).]
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