Pinhole rifle sighting, pinhole glasses, and pinhole selfies
Jearl Walker www.flyingcircusofphysics.com
July 2015 With normal vision, a person can clearly see a nearby object and a more distant object, but not simultaneously. To shift from reading a book to seeing a car down the street, I have to adjust the focusing of my eyes, which I do subconsciously by changing the muscle that controls the shape of the lens inside each eye. When I aim a rifle, I need to line up the target (which might be 20 meters down the shooting range) and also the front and rear sights on the rifle, but I cannot see all three things simultaneously --- at least one of them is blurred.
One solution to this common problem is to mount a pinhole device just in front of my shooting eye. By looking through the pinhole I greatly increase the distance through which objects are simultaneously in focus (or nearly in focus). The advantage of the pinhole is that it decreases the angular range of light rays coming from an object and reaching the retina at the rear of the eye.
Suppose I look at a nearby point source of light and a more distant source. If I adjust my eye so that the more distant source is in focus, then light rays from it form a small image on the retina.
However, the light rays from the nearby source then “attempt” to form their image behind the retina.
So, those light rays from the nearby source illuminate a larger region of the retina, and what I see is a fuzzy image of the nearby source.
If I then place a pinhole just in front of my eye, the pinhole allows only part of the light rays from the nearby source to reach the retina. Thus the illuminated range on the retina is smaller and I see a sharper (though dimmer) source.
Pinhole glasses have very dark plastic “lenses” with many pinholes (or tiny clear circles) through which light is transmitted. Suppose a person is far sighted and cannot read a book page. By looking at the page through the pinhole glasses, the letters produce smaller images on the retina and are thus much less fuzzy. This advantage of pinhole glasses has long been known, but unfortunately many false claims have been made about the glasses altering vision in a permanent way so that the person moves toward perfect vision. They do no such thing. For example, this video recommends that you “exercise” the muscles of your eyes for 15 minutes a day by using pinhole glasses. There is no medical evidence that the eyes change.
Pinhole cameras are still popular even though most designs require photographic film, which is no longer common. Still, they are fun and easy to make, even with a small box. A pinhole is punched in one side of the box, with opaque tape placed over the hole. In a dark room, film is then mounted on the inside wall on the opposite side of the box. The box is kept closed and the pinhole is kept covered until a photograph is to be made. Then the tape is removed. Light from the subject can then enter the box and record an image on the film. Experience is needed to know how long the film is to be exposed, but several minutes are usually required because of the low illumination entering the box.
Recently photographic artist Ignas Kutavicious developed a technique of using a pinhole camera to take a selfie (self image). Here you can see him posing with its equipment.
The drawback is that the person being photographed must remain still for as much as five minutes in order to expose the film sufficiently. Here is a gallery of some of his work:
http://www.gunsamerica.com/blog/the-envelope-please-my-best-rifle-sight-award-goes-to/ Longer description of pinhole sights for rifles
Dots · through ··· indicate level of difficulty
Journal reference style: author, journal, volume, pages (date)
· Baez, A. V., "Pinhole-camera experiment for the introductory physics course," American Journal of Physics, 25, 636-638 (1957)
· Young, M., "Pinhole optics," Applied Optics, 10, 2763-2767 (1971)
·· Young, M., "Pinhole imagery," American Journal of Physics, 40, 715-720 (1972)
·· Young, M., "Zone plates and their aberrations," Journal of the Optical Society of America, 62, 972-976 (1972)
· Walker, J., "The pleasures of the pinhole camera and its relative the pinspeck camera" in "The Amateur Scientist," Scientific American, 245, No. 5, pages 192-200 + 202 (November 1981). Available at http://www.wesjones.com/pinhole.htm
·· Young, M., "The pinhole camera: imaging without lenses or mirrors," Physics Teacher, 27, 648-655 (1989)
··· Hogert, E. N., M. A. Rebollo, and N. G. Gaggioli, "Directional image processing using a pinhole camera with a rectangular aperture," Applied Optics, 30, 1361-1365 (1991)
·· Rabal, H. J., and G. M. Bilmes, "Double-slit camera," Applied Optics, 32, 2219-2221 (1993)
· Jakovidis, G., "A pinhole imaging experiment," Physics Teacher, 31, 500 (1993)
· Cabe, P. A., “A ping-pong ball camera obscura,” Perception, 32, No. 7, 895-896 (2003)
· Cepic, M., A. G. Blagotinsek, and N. Razpet, “Looking through pinhole glasses with a digital camera,” Physics Teacher, 46, No. 3, 186-187 (March 2008)