During the course of these last trainings we made two significant discoveries with the teachers. One involved the colors of light and pigment. We have only two pratika involving colors: making rainbows and spectra with sunlight, and observing afterimages from staring at colored shape (the ‘Bird in the Cage’ exhibit at the Exploratorium). This is a woefully inadequate treatment of this important topic, but all the other activities I know from my country require either fancy filters, fancy markers, or a dark space to shine and mix colored lights.
We’re working on making these elements accessible, but meanwhile we also point out that every video screen is composed of tiny pixels of red and blue and green: the primary colors of light. These create the thousands of colors you see on that screen, and are linked directly to the cone nerves in your retina.
Screens’ pixels exploit the limits of your eye to resolve tiny things at a distance. Bringing a magnifying glass up to a white screen can show the pixels, as can flicking some water on the screen, because each drop becomes a tiny lens. (If no one is looking, you can even spit gently on your screen – right now, try it! – and see this effect.)
Well, it seems in Timor-Leste, which has largely leapfrogged the age of landlines and wired telephones, mobile phones are more common than magnifying glasses, and we found that on many phones if you press the phone’s camera up against the screen, the image shown on the phone screen is a clear grid of pixels, red and green and blue! Then click the photo and you have it forever, in digital form! Astonishing.
Two years back we found that you can pop the lens off the front of the toy lasers you can get for 50 cents in local shops and tape it to the phone’s camera to get a microscope of pretty impressive quality considering the amount of work it took to make it. If you view the pixels through this added lens, they’re even bigger!
Likewise, if you press a phone’s camera onto a color printed page, many times you can resolve the ink dots of the three primary pigment colors – cyan, magenta and yellow – in the camera’s image. Up until this discovery, this was the realm of microscopes.
The other astonishing find was also in the area of optics. In these final trainings we presented our lens pratika as we have so many times before, but this time we got a shock. In general we light a candle and look for the real images formed on paper, and look through the lenses to view virtual images. This time, one of Mestre Luis’s groups found a real image behind the candle. The arrangement was: paper – candle – lens. Check out this reenactment; you can barely see the upside-down flame image:
I was at the other training site when I heard about this, and assumed someone was not observing correctly. However, upon meeting up, Mestre Luis reproduced it for me. Absolutely astounding.
I saw that what was happening could not be due to the transmission of light through the lens, but rather a reflection of light. It was actually the exact same set up we use to view a real image from a spoon, which is a concave mirror. Thus, something concave was reflecting the candlelight and focusing it to an image.
There was only one thing in this position, and that was the lens itself. It was a convex lens, so even though the front surface was reflecting some of the candlelight, it could not have been forming a real image. It must be then, that some light from the candle is reflecting off the back inside surface of the lens, which is a concave surface.
I have a plan to test this theory by scratching the back surface of the acrylic lens with course sandpaper, thus destroying the smooth inside reflective surface. Lenses aren’t so easy to come by here though, so I’m currently trying to dream up a different way to prove my theory. If you put your eye nearby the image, you can see a faint virtual image in the lens, but this is entirely unsatisfying. I want something concrete and undeniable. Wish me luck, and try these pratika for yourself!