Materials
- Page Size Fresnel Lens
- Strong Cardboard
- Matt Black Paint
- Ruler, Pencil, Craft Knife
Overview
The projector consists of two boxes, an outer box (shown in yellow in the picture), and
an inner focusing box which holds the lens (shown in red). The inner box fits snugly
inside the outer one, and can be moved in and out to focus the image.
Step 1
First we need to make the outer box. Cut out four pieces of card, two
of which are 46cm x the height of your TV screen, and two which are 46cm x the width of
your TV screen.
Now paint one side of each piece of cardboard with the matt black
paint.
When the paint is dry, assemble the four pieces into a box shape with
the duct tape. Make sure the black sides are on the inside of the box, and ensure there
are no gaps along the edges where light could escape.
Step 2
The focusing box needs to be slightly smaller than the outer one, so
that it can fit inside.
Again, cut out four pieces of card, this time two of them should be 23
cm x 0.5 cm less than the height of your TV screen, the other two 23 cm x 0.5 cm less than
the width of your TV screen.
So if your first box had two pieces of card that were 46 cm x 40 cm,
and two that were 46 cm x 30 cm, this time you would need two pieces that are 23 cm x 39.5
cm (40 cm 0.5 cm), and two that are 23 cm x 29.5 cm (30 cm 0.5 cm).
Finally you need to make the board that will hold the lens. Cut out a
piece of cardboard that is 1 cm smaller each side than the size of your TV screen. If your
TV screen is 40cm x 30 cm you need to make this piece 39cm x 29cm.
Now draw two straight lines from the corners of the board to find the
centre and draw a circle with a radius of 8.5 cm. Cut out and discard the circle.
You should now paint one side of each of the five pieces of cardboard
with the matt black paint and wait for it to dry.
Now tape the lens to the back of the board with the hole in it (the
black side) making sure that it is central. The hole should match up exactly with one of
the circles on the lens.
You can now assemble the box. Tape the four side pieces together in the
same way as you did the first box, making sure that the black sides are on the inside of
the box. Next place the lens board inside the box, about 3cm from the end and tape it into
place. Make sure the lens board is completely vertical, not at an angle, and that the
black side is facing inwards.
You must ensure that there are no gaps around the edges of the pieces
of card that could let light escape.
You should now have two boxes both completely black on the inside. Just
slide the smaller box into the larger one and your projector is complete (and should look
something like the picture on the first page).
Step 3
To use your projector, turn your television upside-down and tape the
box to the edges of the screen making sure that there are no gaps.
This will not harm your TV. If the colours look inverted when your TV
is the wrong way up, leave it turned off for ten minutes and then turn it back on, the
colours will have corrected themselves.
Find a suitable distance for your projector to be from your wall or
screen and move the inner box in or out to focus the image. It may take some time to find
the best position and focus adjustment, have patience and dont be afraid to
experiment with different distances.
You will find that your projector works best if you turn up the
brightness level on your TV to its highest. You need to use the projector in a
completely dark room.
A silver projection screen with a black border will give the best
results, but a light coloured wall will also work.
The image you see will be reversed, if this is a problem turn the
projector sideways and place a mirror at 45 degrees straight in front of it. This will
correct the image. |