Using X-Ray Film in Pinhole Cameras
In essence, a pinhole camera is a light-safe container with an extremely small light leak. Indeed, an image is produced due to the miniscule size of the aperture. For our final project we decided to explore the magical world of pinhole photography. In doing so, we opted to construct a pinhole camera and test multiple variables in conjunction with X-ray film. We plan to prove that increasing the pinhole size will necessitate a shorter exposure time, and an increased focal length will result in a larger image. By constructing a pinhole camera with a light safe box using a thin aluminum sheet with varying hole sizes placed over a larger hole in the camera, we will be able to test our hypothesis. We will create a camera in which X-ray film can be used as a viable alternative to silver photography. The lighting variable will be eliminated by using a light meter to ensure a consistent level of light.
Procedures and Results
A pinhole camera consists of a light-safe box or cylindrical containter (coffee can, oatmeal box, peanut can, sody-pop can), to which a pinhole is attached. We found that the simplest way to construct a camera with changeable pinhole sizes is to cut a larger (1/2 in. x 1/2 in.) hole into the container and place a square inch piece of thin aluminum sheet with a pinhole over the larger hole. Deciding against our first plan to construct a camera with which we could alter focal length, we opted for three ready-made cameras of varying focal lengths. The smallest, a peanut can, was 4 1/2 inches from pinhole to film, the box, 7 inch focal length, and the third, 10 inches.
Our first step was to conduct light tests to ensure that the containers were leak-proof. After numerous trials where we exposed the camera to light without lifting the shutter, we subsequently corrected all leaks. Now, we are finally ready to take some pictures! All of which, we decided, would capture the beauty of nature on X-ray film.
Our first few photos were spent perfecting the pinhole camera picture-taking process. These trials were blurred and indistinguishable due to shaking hands while taking the picture, over/underexposure, operational errors, etc. Finally, we were able to take a relatively clear photograph. We used the rectangular camera with a focal length of 7 inches and a pinhole size of 0.01 inches. Surprisingly, after so many failures, this negative image turned out quite well; the image of the tree in front of Woods is quite distinct, but the details and resolution are not as clear as we had hoped. For this photo and all the others we took, we used a two-second exposure time on a bright, sunshiny day. For the developing process, we used a 4:1 water to Dektol ratio and two minutes in the developing bath, and thirty seconds in the stop and fixer baths.
Using the rectangular camera, this time with a pinhole size of 0.02 inches, we set out again for the outdoors, this time capturing the picturesque back door of Carnegie and the scenic lampost in front of it. Using identical exposure times and developing procedures, it was not surprising to discover that this photo had a greater resolution and sharper details, as is evident below. Also evident below is our incompetence at cutting film in the pitch-black "dark"room.
Sensing that our photographic skills could not possibly surpass those displayed in this photo, we decided that the conditions used here were optimum. Therefore, we deduced that a slightly larger pinhole size allows more light in. A slight increase in this variable can make more distinguishable details. We also determined that, from these two tests, 7 inches is an optimum length in order to create a well defined image on x-ray film. Now, let's see about those other two cameras...
Our first attempts using the cylindrical camera with the 4 1/2 inch focal length were also extremely distorted. The first, using a 0.01 inch pinhole size and of the same tree outside of Woods as used in the box camera, was overexposed and shaken, resulting in its apparent fogginess and blurriness. Given that light intensity decreases the further it travels from the pinhole, this photo appears to have also been flooded with light. The majority of the developed film was clear and indistinct.
Our next attempt, the middle photograph, we took hoping to eliminate variables which we were not testing. We decreased exposure time and were sure to hold the camera steady. The results were much improved but still not ideal.
For our third photo, we increased the size of the pinhole to 0.02 inches. This resulted in a significant improvement in clarity. Therefore, we determined that a slightly larger pinhole size than 0.01 inches is necessary in a camera with a focal length of 4 1/2 inches.
Unfortunately, these photographs, taken with the 10 inch focal length, cylindrical camera, are even more difficult to distinguish due to the scanning process.
The first photograph was exposed for only two seconds, which was clearly not enough for a distinct picture. After many attempts to determine just what the problem was, we referred to Mikrut and Connors' chart calculating ideal pinhole size to focal length ("Pinhole Photography: Rediscovering a Historic Technique" Eric Renner, Focal Press, Boston, 1995). By using their recommended 0.02 inch pinhole size, we eliminated one factor to focus on the more apparent one -- exposure time. As Joy Reeves comments in her pinhole project last year, a longer focal length requires a longer exposure time. Therefore, we increased the exposure time to 4 seconds, eventually reaching the clarity of the third photo on the left at a 5 second exposure time.
We succeeded in finding ideal conditions for X-ray film in pinhole photography after numerous trials. The box, at 7 inches in focal length, and 0.02 inch pinhole size, creates a large, well-defined image. For this camera, we found that a two-second exposure time is adequate in most outdoor lighting. We found that the shorter focal length of the smallest camera was not well-suited for use with x-ray film. Despite varying pinhole size, we still often overexposed the film even when the exposure time was reduced. For the biggest camera, we saw that the longer focal length resulted in reduced clarity given that less light reached the film.
Our final project did not vary much from our original plan. We were correct in our prediction that a longer focal length would result in a larger image. However, our experiments revealed that exposure time was affected more by focal length than pinhole size. As was our original plan, we created a camera in which x-ray film can be used as a viable alternative to silver photography.
Reeves, Joy. Pinhole Photography.
Renner, Eric. Pinhole Photography: Rediscovering a Historic Technique. Focal Press, Boston: 1995.
Wolfe, Amanda. Silver Photography with Pinhole Cameras.
Cynthia Heller, Heather McAdams, 1998.