PROJECTION ADDITIONAL INFO & RESOURCES

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Inversion of image

Most plans will tell you to turn your TV or monitor over. Kids, don’t do this if your TV is 19” or more. If you do and your picture turns green there’s a reason – Normal TV’s and computer monitors are not meant to be turned upside down. The only exceptions would be new flat screen LCD monitors. Here’s the smart way to flip the image back around.

It’s possible to use 2 mirrors at 45 degree angles to flip the picture back around. We’ll be posting plans soon on how to add a third box to add these.

Mirror on the wall - Front Surface Mirrors

Everyone is familiar with going to the movies and seeing the image projected from the rear of the auditorium to the screen at the front of the room. Any type of projection system, whether film or video is the same: you create the image, magnify it, and project it through a lens to the screen. Unfortunately, even with custom tailored lenses, you end up with the "throw distance", or the distance from the projector to the screen being too long. Imagine trying to fit a rear projection television in your living room with a throw distance of ten feet! The cabinet would be huge, the cost would be enormous, and there would be no room for the couch and your coffee table!

To get around this, engineers and optical designers use what is called a "folded optical system» that uses "short throw" special lenses in conjunction with mirrors to literally "fold" the optical path so that while the image's light path travels the same distance, the use of the mirror allows you to have a shorter cabinet depth by cutting the path in half.

This type of design is what has led to the popularity of rear screen projection systems, but to make certain that light is not lost to internal reflections. Conventional mirrors, like the ones you probably have in your home are typically "rear surface" mirrors, meaning that the silvery material that gives the mirror its reflective properties is applied to the rear of the glass surface. This is great for checking to see if your hair is combed properly, or if your tie is on straight, but when light passes through the glass once, and is then reflected back out through the glass surface a second time, the light tends to scatter, resulting in the image losing focus. The mere fact that the image travels through the glass twice also results in a loss of brightness because the some of the light is absorbed during each pass.

To eliminate these problems, projection televisions uses special front surface mirrors, made using a process that applies the reflective material to the front of the glass, rather than the rear. This way, the light image bounces directly off the mirrored surface without having to travel through the glass, thus avoiding losses and scattering. This assures a crisp, clear, bright image.