Cheap solar projection
Michael Garrahan
made from two pieces of flat cardboard.
It works, but I wanted higher contrast, so I used a cardboard tube to
cut off ambient light as I attempted to describe in an earlier posting.
zcr...@warren.med.harvard.edu (Zak Cramer) tactfully asks for clearer
instructions for building such a tube.
>And: does this really work?
Yes. Since you asked, I just built another one, and I revised the
design slightly. The contrast is good, but the resolution isn't so
great. That's why I asked about the feasibility of using a stopped-
down eyeglass lens. Also it might do better if the screen were not
viewed from behind, but I couldn't think of a way to make that easy
to use and still block ambient light.
Parts:
Cardboard tube from a roll of paper towels ("long tube"), 28cm long,
42mm diameter
Cardboard tube from a roll of toilet paper ("short tube"), 12cm long,
42mm diameter
41mm diameter circle of tracing paper
6cm diameter circle of flat cardboard with a pinhole in the center
2cm square of aluminum foil (optional)
Black construction paper rectangles 25x13cm and 11x13cm (optional)
Cellophane tape and masking tape
Larger tubes may be used if you adjust the dimensions of the other parts
accordingly.
Assembly:
1. Place the flat cardboard circle over one end of the long tube and
seal them together with masking tape around the outside.
2. Make six or eight lengthwise 2cm cuts in the open end of the long
tube and spread the resulting flaps outward slightly.
3. With four or six small pieces of cellophane tape, attach the tracing
paper circle over one end of the short tube.
4. (optional) Roll the black construction paper rectangles into
cylinders, turning the 13cm edges into circles, and use them
to line the insides of the cardboard tubes.
5. Insert the covered end of the short tube in the widened open end of
the long tube until the tubes fit together snugly.
6. Wrap the outside of the widened end of the long tube with masking
tape. You need not tape the two tubes together; friction will
hold them.
7. (optional) Tape the piece of foil over the pinhole in the flat
cardboard on the end of the long tube. Rub the foil with your
finger to make a dimple over the hole in the cardboard. Make a
small pinprick in the foil there.
Usage:
Point the pinhole end of the long tube at the sun and look in the open
end of the short tube with one eye while you cover the other eye. If
your eyes are myopic but not badly astigmatic, you may want to view
without your glasses.
Long tube Short tube
|-----------------------------===---------
Sun | |
O | | > Your eye
| |
|-----------------------------===---------
^ ^
Cardboard Tracing
with Paper
Pinhole
Criticism and suggested improvements are welcome.
Mike Garrahan
mgar...@bev.net