Where a lens forms an image by bringing rays of light coming to it from each point in the subject to a common focus, the pinhole does not focus at all. Instead, it acts as a center of projection.
Speaking practically, a ray of light from any point in the subject, passing through the pinhole, will intersect the film in only one place. Another ray of light, coming from a different point in the subject and passing through the hole will strike the film in a different place. The accumulation of all rays of light passing through the hole will thus form an image at the film plane. If the film plane were moved forward or backward, the image would still be there, but it would be smaller or larger depending upon where it were located.
Because the hole is actually not truly a point, it allows more than just one ray from each point in the subject to strike the film. We could say that it passes a small bundle of rays from each point. This is one reason why pinhole images are characteristically softer than lens images. The other reason is that some of the rays encounter the edge of the hole and are diffracted; they bend.
Since there is no focus, the sharpness of the image (such as it is; it is always somewhat "soft") is uniform from near distance to far. In other words, there is no limitation of depth of field as there is in lens photography. Very near objects (closer than the pinhole to film distance) will however become softer due to divergence of the rays coming from each point.
The other requirement is a suitable pinhole. This can be made with or without a great deal of precision; the quality of the image will vary tremendously according to how the hole is made. One of the most common materials for making pinholes is brass shim stock or other very thin metal. There is often a great deal of discussion about methods of making the actual holes. Both the "pokers" and the "drillers" have their reasons for preferring their respective methods.
Various materials such as black fabric, black paint, black tape, etc. are needed to eliminate internal reflections and simply hold the parts together. If you wish a viewfinder on your camera, you may design and construct one but the camera will work whether or not you know what it is seeing.
One of the easiest ways to make a functional pinhole camera is to drill a hole in a body cap that fits a camera that uses interchangeable lenses. Over this hole, it is possible to tape a piece of metal in which an imaging hole is made. The lens is removed from the camera and the body cap inserted in its stead. In this way, it is possible to use the camera's existing film transport mechanism. Film exposed in such a camera can be sent to a photofinisher for processing and printing, or finished by the photographer. This makes it possible for persons not having darkroom capabilities to practice pinhole photography.
In recent years commercially marketed cameras have become available. Some of these are truly quite excellent. For some pinhole photographers, though, designing and building the camera is a very large part of the medium's appeal. It has b een said, for that reason, that pinhole photography is part photography and part sculpture.
Materials needed to make a pinhole
Let's Do it!!!
The first thing that has to be done is to insert the needle into the eraser-tip of your #2 pencil. Get out the scrap of 5" cardboard. Put it on a firm surface (the table or floor will do fine). Now grab the #2 pencil and hold the pencil vertical (straight up and down) in one hand, and hold the #10 sewing needle vertical with your other hand. Center the needle on the eraser-tip end (eye end of the needle towards the eraser) and then with a downward push (using the cardboard for a place to push the sharp part of the needle into) get the needle started into the eraser tip. You might have to try a few times before you get it to look like example #1.
|Example 1||Example 2||Example 3|
But it is worth getting it as straight as possible. Pull the needle back out of the eraser and start again only if you have to!!! When you are satisfied that you have it started straight, use the needle nose pliers or "needle grabber" to sink it in as far as it will go into the eraser tip.
Get out the .003 brass shim stock and lay it on the cardboard (find a fresh spot on the cardboard). Start twirling the pencil-needle tool (from now on just called the needle), like you see in example #2.
Make sure you are in the center of the brass shim stock square. Important note: The cardboard is not seen in the drawings, just imagine that it is under the brass shim stock). You will start to go through the brass shim stock as you twirl and push downward ever so slightly in a drilling motion. You can now see the needle coming through the brass shim stock as in example #3.
Pull the needle back out and you will see that you now have small burrs on the opposite side that you started from. See example #4.
These burrs are what you will now need the 400 grit emery paper for. Sand the brass shim stock on the burred side going in a gentle circular motion with your emery paper until the burrs are gone (don't over do this step).
Now you want to flip the brass shim stock over to the opposite side (the side that you just sanded the burrs off of). Insert the needle into the hole and repeat the twirling motion as shown in example #5.
|Example 5||Example 6|
This time you will get very little burrs on the opposite side that will look similar to those in example #4, but not as pronounced. Sand these burrs off the same way as you did earlier being ever so gentle. When you are satisfied that you have removed those burrs , stick the needle back into the hole (from the opposite side of the brass shim stock) and then CAREFULLY twirl the whole square piece of brass shim stock as shown in example #6.
It should twirl pretty easily and yet still be snug. When you have gotten to this point you may or may not have to sand some more ultra small burrs if they do show themselves on the opposite side from where you last inserted the needle. If need be, sand them!
At this point all you need to do is get out the loupe or magnifying glass and check to see if you have a nice CLEAN pinhole. If you do you are finished. If not repeat inserting the needle into the hole on the opposite side of the brass shim stock and give it another good twirl like in example #6, until you do see a good clean pinhole!!! Congratulations you now have a pinhole and know how to make one too, way to go!!!
Optimum pinhole diameter in inches = 0.0073 * SQR (focal length in inches) SQR stands for square root. For metric system the formula becomes: Pinhole diameter = 0.03679 * SQR (focal length) where diameter and focal length are in millimeters
Once you know the size of pinhole you will use, find the f/stop of your camera by dividing the focal length by the diameter. Obviously, both values must be in the same unit of measurement.
f/stop = focal length / diameter
More likely than not, the f/stop won't coincide with a full stop. Since the progression of f/stops is not linear, to find where exactly in between stops the f/stop of your pinhole camera is, you'll need a mathematical formula to calculate it. But that isn't necessary due to the "imprecise" nature of pinhole. I would suggest you approximate the calculated f/stop to the next full stop (unless is really close to lower one). The reason is that pinhole exposures are more likely to be under than over-exposed.
The second method is taking an actual light reading of the scene. Sometimes I use a handheld meter, other times I use my 35mm camera. Let's call "f" and "t" aperture and time, respectively . Once you have the exposure that your scene needs, you have to find the equivalent exposure for your pinhole f/stop.
You then start to double "f" until you get a value that is equal or bigger than "F". If equal, the number of doublings multiplied by 2 is the number of f/stops separating "f" from "F". If bigger, the number of f/stops between "f" and "F" is the number of doublings time 2 minus 1. The new exposure time ("T") will be obtained by doubling the time "t" as many times as stops separate "f" from "F". It is more difficult and cumbersome to say it, or write, than to actually do it.
Let's use an 11x14 format, 6" focal length camera as an example:
Optimum pinhole size = 0.0073 * SQR(6) = 0.018" (approx.)
f/stop of your camera = 6 / 0.018 = 333
progression of f/stops from f/16 to above f/333 is : f/16, 22, 32, 44, 64, 88, 128, 176, 256, 352.
practical f/stop of your camera = f/352
Scene to photograph is under sunny conditions, material used as negative is B&W multigrade paper. Approximate ISO speed is 6. Therefore, using Sunny16 we should expose for 1/6 secs and f/16.
To find the number of stops separating f/16 and our camera f/stop of f/352, we double 16 until we get 352 or above. It takes 5 doublings to get to 512 (32,64,128,256,512). Since 512 is bigger that 352, we then find the stops separating f/16 from f/352 by multiplying the number of doublings times 2 and subtract 1 -- 5 times 2 = 10 minus 1 = 9 there are 9 stops between f/16 and f/352. Now we find the new exposure time by doubling 9 times our time of 1/6 sec: 1/6, 1/3, 1/1.5, 1.33, 2.66, 5.33, 10.66 , 21.33, 42.66, 85.33.
The new exposure time is then = 85 seconds.
The equivalent exposure time to f/16 and 1/6 sec is f/352 and 85 seconds. I wish this were the end, but the exposure time of 85 seconds has to be corrected for reciprocity failure. There is a table that has proven very effective for me. Watch out for sailing clouds, as you might have to increase the exposure time a little more if a big one passes by. When I was making the photograph "door", the uncorrected exposure time was 8 minutes. The multiplier according to my reciprocity table is 5 for a corrected time of 40 minutes!!! A big cloud passed by during part of the 40 minutes. I extended the time to 55 minutes to compensate. Negative material was Ilford Multigrade.
I'd like to finish saying the following: I am not an artist. I am a technician. All my studies and jobs have been in tech things (electronic, electricity, communications and computers). Nevertheless, I feel the need, sometimes the urgency, of "creating" something beautiful to me, for me and by me. To accomplish it, my idiosyncrasy request from me to learn, to the limits of my incompetence, all the science that makes pinhole work. This knowledge serves to me as a ladder to try to reach the high er plateau on which art is. Some other people are born artists, some other are lucky enough to have a very eclectic mix. The science behind pinhole, as boring and not necessary that it is for some, it is indispensable and/or interesting and /or unenjoyable f or others.
Star Route 15, Box 1355
San Lorenzo, New Mexico 88041
Tel: (505) 536-9942
(membership: incl. curators, historians, educators, students, photographers, camera clubs etc.) Also sells cameras and other pinhole related items, such as books, drilled pinholes in various sizes, zone-plates, etc. Also run workshops.
George L Smyth
Gordon J. Holtslander
Prepared for translation by Gregg Kemp in 2003.