Thursday, 20 June 2013

Sitting in a Pinhole Camera

Pinhole cameras are the simplest camera possible, made up of only a pinhole and a screen or film. They don't even need a lens. The camera works by line of sight and the fact that light essentially always travels in straight lines. For every point on the film there is a single line of sight, out through the pinhole, to a point in the world outside the camera. Only light from that point in the outside world can get through the pinhole and hit the film, which is the way in which the image is made. This simplicity means that you can make a pinhole camera incredibly easily. All that is needed is:
  1. A dark container or enclosure. 
  2. A small circular hole in one side of the container. 
  3. A screen or film to detect the light. 
The first two of these are easy to make at home, but the third isn't. Who has a spare piece of film and developing solutions? The [other] solution? Use a person to detect the light and see the image directly, or sketch it on the screen. The problem with people is they are pretty big, you can't squeeze one into a shoebox. Let's make a bigger pinhole camera then, one the size of a room. A room-sized container is easy to find, it's called a room!

A room sized pinhole camera!

The ability of a pinhole to project an image of a scene has been known for over 1000 years, and was first clearly described by the Persian philosopher Alhazen. These ancient scientists faced the same problem detecting light and initially used darkened rooms or tents with a pinhole in one side, then traced the image projected by the pinhole by hand. These devices are called camera obscura, the Latin literally meaning darkened room!

Turning a room into a pinhole camera takes just three easy steps:

1. The dark enclosure 
A pinhole camera container has to be light proof to prevent light leaking in and spoiling the image. The best thing for light proofing a room is aluminium foil which is very opaque for its weight and thickness. Foil tape is also excellent for blocking smaller gaps. 

2. The pinhole
There are a few rules for pinhole size; the bigger it is, the brighter the image. There is simply a larger gap for the light to get in. Unfortunately larger pinholes give a more blurred image because it increases the range of angles at which light can pass through the pinhole and hit a particular point on the film or screen. The pinhole also can't be too small else diffraction of light will start blurring the image. Practically for a room a "pinhole" around 1.5-2.0 cm in diameter will let in enough light to see the image clearly, but be small enough to give quite a sharp image.

3. The screen or film
In a room-sized pinhole camera you just need to sit in the room to see the image!

Foil blocked windows and a pinhole, the shaft of light is from the sun.

The image in a pinhole camera is inverted (upside down). This is because for light to reach the top of the film after travelling through the pinhole it has to be travelling at an upward angle; the line of sight through the pinhole means this is a view of the ground. Similarly for the light to reach the bottom of the film after travelling through the pinhole it has to be travelling at a downward angle, in this case giving a view of the sky. The upshot of this is that in a room sized pinhole camera the floor is a sea of clouds with an inverted picture of the world outside projected on the wall.

The pinhole image the right way up...

... and upside down. The same way up as the image.

You can literally sit in the clouds!

Software used:
UFRaw: Raw to jpg conversion of the raw camera files.

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