DIY: Projector With a Fresnel Lens

Written by shoaib khan
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DIY: Projector With a Fresnel Lens
Enjoy movies on a big screen from a simple homemade projector. (Filmstrip countdown - Number on 2 image by Andrew Brown from Fotolia.com)

You can watch movies and TV shows on a big screen by building a simple and inexpensive homemade projector. Building a homemade projector entails placing a magnifying lens in front of the TV screen, so that the images onscreen are magnified and projected. Although a standard double-convex lens can be used as the magnifying glass, a Fresnel lens will give the best results. A Fresnel lens is essentially a modified double-convex lens that is constructed by dividing the lens into numerous concentric circles, thereby reducing the curvature of the lens and forming a flatter shape. Unlike a standard lens, a Fresnel lens eliminates distortion of the projected image because each part of the lens can project the whole image from the screen.

Skill level:
Moderate

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Things you need

  • Ruler
  • Cardboard or plywood
  • Fresnel lens
  • Box-cutter
  • Tape
  • Black paint

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Instructions

  1. 1

    Determine the dimensions of your TV. Use a ruler to measure the length, width and height of the TV set, and not just the screen itself. You will need the measurements because you will have to construct a box that can house the TV.

  2. 2

    Cut four pieces of thin plywood or cardboard for the walls, according to the dimensions of the TV. Tape (or nail) the pieces to one another so that the four walls are held firmly. When completed, the box should have four walls and two open sides. You should be able to slide the TV inside, so that the back of the TV sticks out from one of the open sides and the screen can be viewed from another open side. Slide the TV in and check whether the walls of the box fit tightly. Adjust if necessary.

  3. 3

    Cut four pieces of thin plywood or cardboard for the second box, taking into account that you will need smaller wall sizes than the first box. You will need smaller walls because the second box should fit into the front of the first box. Another difference is,unlike the first box which has two open sides, the second box will have only one open side---the back. Tape (or nail) the sides together to form the box. Slide the second box into the front of the first box and check whether you can move the smaller box in and out freely. This arrangement will allow you to change the size of the projection and focus the projected image, as you move the box in and out.

  4. 4

    Place the Fresnel lens in the centre of the front wall of the smaller box and draw around it. Use a box cutter or knife to cut along the drawn line. The hole should be large enough to hold the lens firmly in place. Mount the lens and check whether the hole needs to be larger. If the hole is too large, use padding to hold the lens in place.

  5. 5

    Remove the TV from the first box and the lens from the second box. Place the boxes upright, away from the TV and the lens, and spray paint the inner walls of the boxes with black matt paint. This will ensure that the walls do not reflect the TV screen and interfere with the projection.

  6. 6

    Slide the TV inside the larger box, mount the Fresnel lens onto the front cover of the smaller box, and slide the smaller box about halfway inside the larger box. After reassembling the projector, the TV screen and lens should be facing a bare white wall or a projection screen.

  7. 7

    Turn on the TV and adjust the projection. Check whether the projected display is distorted, dull or blurry. Configure the focus by moving the smaller box in or out of the larger box, and change projection size by moving the projector away from and closer to the projection screen. If the display is dull, make the room darker or move to a room with low lights.

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