Tuesday 3 March 2009

Tiny Circles

Just reviewing a note about the wonderful property of pinholes. If you are in a well lighted room, look at a sign or picture far across the room. If your eyes are old like mine, it may not be very clear. If you have great eyes, pick out a small object that is difficult to see clearly. Now punch a small hole in a 3x5 card or piece of paper with a thumbtack or such. Hold it up in front of the eye and look at the object through the hole. If you move it back and forth a little, you should notice the object is in much sharper focus... WHY???

As light strikes the eye it has to be brought to bear on a single point on the retina to foucs sharply. By looking though a tiny hole, the light is all falling on a very small spot, and thus is much sharper. It does reduce the total light, so the object has to be pretty bright.

You can do the same thing by squeezing the thumb and finger together (like you are signing OK) on both hands and then push the two thumbs and fingers together. They form a little diamond shaped hole in the center, and if you peer through this, it will have the same effect. Press a little harder to make the hole smaller and the image sharper. I use this sometimes in the underground to be able to read the tube maps on the opposite wall when they aren't clear.... and it works..

I just learned that "it was the 10th-century Arab physicist, astronomer and mathematician, Ibn al-Haytham (Alhazen), who published the principle of the pinhole camera in the Book of Optics in 1021 AD. He also invented the first pinhole camera after noticing the way light was streaming through a hole in a window shutter. He improved on the camera after realizing that the smaller the pinhole, the sharper the image. He went on to designed the first camera obscura (Latin for something like Shadow room).

1 comment:

Pat's Blog said...

It eliminates rays from the edges of the pupil...because they are bent more, the rays that pass near the edge of the pupil are more blurry. Squinting can eliminate those edge rays and you will have a little less blurring.

Not sure that is the total answer... but part of it..