I have recently come across what I would describe as the best low-cost (around 4 dollars) pinhole star projector that I have seen to date—a Kenko Star Roman star projector.
The projector was originally fitted with an incandescent bulb. Since an incandescent bulb does not usually perform well as a light source for pinhole projectors (since it uses a filament that is not exactly round and ‘point source’), I have decided to replace the bulb with an LED, in particular, one with a very small light-emitting material. If you use a typical LED with a large light-emitting material, it will perform no better than an incandescent bulb. It may take some experimentation to find an LED that will work well, but in this DIY project, I have found a suitable replacement from an Eveready flashlight.
The smaller and brighter the light source is, the sharper and brighter the projected images of the stars (perhaps a laser diode will perform much better than a flashlight LED, but that will be for another DIY project).
Shown below is the acetate with printed star patterns. Labels of constellations are written in Japanese.
This projector only shows the stars of the Northern Hemisphere.
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© Anthony Urbano (Manila, Philippines)