Week 5 - Workshop Notes [Pinhole Cameras]*

Pinhole Cameras

Homemade Pinhole Camera

What is a Pinhole Camera?

A pinhole camera, also known as camera obscura, or "dark chamber", is a simple optical imaging device in the shape of a closed box or chamber which is light tight. In one of its sides is a small hole which, via the rectilinear propagation of light, creates an image of the outside space on the opposite side of the box. It is essential a pinhole aperture with no lens.

Making a Pinhole Camera

Constructing a simple pinhole camera is easy. Make a hole in one side of a closable box made of material which doesn't let light in. Place a thin piece of metal or tin can with a tiny hole over the opening. On the outside of the box stick a strip of black tape over the opening which acts as the release. Then, in a dark room, attach a piece of film or photographic paper onto the opposite side and the camera is ready.

The pinhole camera's simple construction offers a number of ways in which it can be constructed, using various materials. The cameras can be all kinds of shapes and sizes, with various formats and types of light-sensitive material, several holes, curved film planes, for panoramic images etc. There are all sorts of imaginative ways to make these cameras; the most ordinary of objects can unexpectedly become pinhole cameras, for example a matchbox, book, a pepper, travel bag, a delivery van, an old fridge or even a hotel room. You can, of course, turn your ordinary camera into a pinhole camera by simply replacing the lens with a small hole.

How Does a Pinhole Camera Work?

The rectilinear theory of light

When the shutter is opened, light shines through to imprint an image on photographic paper or film placed at the back of the camera. Pinhole cameras rely on the fact that light travels in straight lines – a principle called the rectilinear theory of light. This makes the image appear upside down in the camera.

If the dimensions of your camera and the size of your pinhole are correct you can take a photograph that will compete on a technical level with a photograph from your digital SLR camera. A small pinhole generally produces sharper images than a larger one. However, if the pinhole is too small, light waves may be scattered slightly at the edges of the pinhole and cause distortion or loss of focus. 

Smaller holes also increase exposure times, since they will let less light into the camera.

Focal Length of a Pinhole Camera

Focal Lengths and Angle of View with a pinhole camera

The focal length of your pinhole camera is the distance between the pinhole at the front of the camera and the paper or film at the back of the camera.

Therefore, the shorter the distance between the pinhole and the film, the smaller the focal length will be as well as having a wider angle of view and vice versa for longer distances. The diagram below depicts this.

Long focal lengths with pinhole cameras give a telephoto effect but will need longer exposure times than smaller focal lengths.

Vignettes

When the light enters the pinhole at the front of the camera, it is projected onto the paper or film at the back in a circle. The diameter of the image circle is roughly three and a half times the focal length. You may end up with a black vignette around the image if you have a shorter focal length. And this may be exactly what you want. 

The vignette appears because light is forced to travel further to the outer edges of the circle leaving it underexposed. If you don’t want this effect, make sure the camera doesn’t require paper that is larger than approximately twice its focal length. 

A camera with a focal length of 3 inches will produce an image with a diameter of approximately 10.5 inches. 

The intensity of the light in your camera decreases as you extend the length of the camera. The light will be stronger nearest the hole and gradually weaken as it continues towards the back of the camera. This means that you will need longer exposure times for telephoto cameras.

Sources:

1. http://www.pinhole.cz/en/pinholecameras/whatis.html

2. From pinhole to print Inspiration, instructions and insights in less than an hour by Gary Fabbri, Malin Fabbri and Peter Wiklund