Now for a hand knitted solution, one likely to be frowned upon by purists. In our own trials a home-made raybox worked quite well. What’s needed are: a small cardboard box; a pocket comb; a torch, and - in true Blue Peter tradition - the ubiquitous sticky tape.
Use a cardboard box of about 19 x 19 x 15 cm or if need be to suit the size ofthe torch which you have to hand. Cut a slot, slightly smaller than the comb, in the leading edge of the box. Then tape the comb across the slot, teeth pointing downwards. Place a sheet of A4 white paper under the comb, switch on the torch to shine through the comb. Et voila! You should now have a series of streaks of light on the paper.
DIY Light Box. No lens in use. No dim-out.
Note that a torch and the teeth of a pocket comb produce slightly diverging, rather than parallel, streaks of light. These streaks are also quite coarse. What do you want for next to nothing?
Place the fat biconvex lens in front of the comb then, try the thin biconcave lens. With luck, and a certain continuity in the laws of physics, you should note how the direction of light rays (or ray-streaks more like) is altered - see the sequence of photographs.
|DIY Light Box with a biconvex lens. No dim-out. Note that the streaks which pass through the lens now come together (converge).||Light Box with a biconcave lens. No dim-out. Note that the streaks which pass through the lens now spread out (diverge) more than before with no lens in use.|