The Pinhole: Nature's Lens
I recently received a call from Tom Lannan of Wasilla asking for information on how his son could build a pinhole camera for a grade school science project. This sounded like a good project, and it reminded me of the interesting history of pinhole optics.
Many Alaskans probably remember the solar eclipse of July 10, 1972. Authorities warned observers not to look directly at the sun, but to view it through dense filters or, preferably, to poke a pinhole in a piece of foil and let the sun's rays pass through it onto a piece of paper. Watching the image on paper is a safe way to view an eclipse, but most people who did it were probably unaware that they were following a practice that has been used, at the very least, since the time of the ancient Greeks.
By Leonardo da Vinci's time in the late 15th century, the camera obscure (Latin for "hidden room") had been used for centuries by astronomers to observe solar eclipses. The camera obscure was literally a small room in which an observer sat. It had a minuscule hole drilled through one wall and a blank white wall opposite. The "pinhole" in the wall focused the image of the eclipse on the blank wall, and observers were able to study the event without damaging their eyes.
Da Vinci used this principle to study the effects of perspective, and by the early 1600s, copycat artists were using it to trace the figures of their subjects who would be seated outside in the sunlight. As time went on, the camera obscure was made into smaller and smaller versions that eventually became the forerunners of the box camera, in which the pinhole was replaced with a glass lens. The blank wall was then replaced by a silver plate with a light-sensitive emulsion which produced a daguerreotype (named for the French painter who originated the process). Thus was photography born.
Some time ago I received a photograph from Yern Seifert of Anchorage that appeared to show a bunch of fuzzy crescent-shaped light spots on a driveway. Mr. Seifert challenged me to guess what the photograph represented, adding that the photo was taken about ten years ago. Remembering the eclipse of 1972, I guessed that the spots were images of the eclipse that had been filtered through tree leaves. Seifert was delighted to tell me that I was right.
Sunlight passing through minor apertures between tree leaves is focused like the rays in a pinhole camera (and, just as with a simple lens, the image is upside-down). Ordinarily, the light spots that we see interspersed in the shadows of trees are round: they are actual images of the sun. During an eclipse, however, the images are crescent shaped, as those seen on Seifert's driveway in 1972.
Pinhole cameras, despite their simplicity, provide nearly distortion-free images and an almost infinite depth of field. Their primary drawbacks are that the images they produce are soft or fuzzy and that they are notoriously "slow." (A typical pinhole camera photographs with an F-number of about 200, while most fixed-focus cameras have an F-number of around 8 to 16).
Although I was unable to provide Mr. Lannan with detailed instructions on how his son could build a workable pinhole camera, I understand that such directions can be found in many photography manuals. In essence, the project involves poking an appropriately sized pinhole (preferably in metal foil) at one end of a light-tight container and securing a piece of light-sensitive film at the other. Exposure time is controlled by opening and closing the pinhole with a piece of electrician's tape or other similar material.
Long exposure times, a steady mount and a great deal of experimentation should be expected to produce results. On the positive side, the pinhole camera produces distortion-free images (buildings don't look like they are falling over backward and squares don't appear as bulgy barrels) and has a great depth of field--advantages not found in some of the most modern equipment.
