Creating a simple camera obscura

The earliest form of 'photography' and use of the pinhole was using a camera obscura (latin for 'better than the telly'). Below is a fast, simple, cheap and wonderfully effective introduction to the wonders of pinhole imaging, achieved by simply blacking out a window leaving a small hole to project an image of the outside world onto your walls and ceiling.

Assembly.

Find a room that can be blacked out. Ideally with a view (with the sun behind) but any will suffice. Measure the window then cut out, (or stick together) some light tight material (black plastic) to a size a bit larger than the window.

Find a length of doweling the width of the window and fix to the bottom edge of the blackout. This enables it to be rolled up and left in place above the window. (Handy for unexpected guests).

Fix the top edge permanently to the top of the window and find a cunning way to fix the edges of the blackout to the window. I'm a gaffer tape man myself but those of you who don't want to ruin your paintwork may want to make use of Velcro, magnetic tape, or some other high tech stuff. However you fix it, make sure it is 100% light tight.

Making the Pinhole.

Choose an area centralish to the window, (but behind a pane of glass). Cut out a 3cm area in the blind and replace it with a square of aluminium with a hole punched through.

Size.

For small cozy rooms with a window to rear wall distance of up to 5m, a 6mm hole (created with a hole punch) is ideal. For larger rooms a 1cm hole could be used. The larger the hole, the brighter the image, but also the less sharp it becomes.

Creating a scenario.

Choose a bright day to show off your new gizmo. It takes a while for ones eyes to get used to the dark so, before someone comes round, roll the blind down, stick a piece of insulation tape (shutter) over the hole and light the room with a candle to allow peoples eyes to get used to the dark.
Invite them in and whilst their eyes are adjusting tell them all about how light works and how stone age men probably first noticed inverted images in their caves and how the gaps in a leaf canopy have been projecting the image of the crescent moon onto the forest floor for millions of years,,,,,,,,,then, whip off the insulation tape et voila! something to chat about in the pub!

To really impress the neighbours you can use a mirror placed just below the hole to reflect the movement of clouds and birds onto your ceiling. (See the badly drawn illustration above right ) You can also play with anamorphs by getting a sheet of paper to show how anamorphs work so recreating an experiment Aristotle did sussing out why the image magnifies when the pinhole image plane distance is increased.

You can also photograph your new decor by positioning a camera near the window and doing a time exposure pointing into the room. (10 minutes to an hour).

Links.

http://www.acmi.net.au/AIC/CAMERA_OBSCURA.html
A fine collection of historical info

http://www.brightbytes.com/cosite/collection.html
More information on camera obscurers

http://www.funsci.com/fun3_en/sky/sky.htm#4
More information on using a room (but he uses a lens which rather lets the side down!).

The Clifton Observatory in my home town of Bristol. A marvellous place although very sadly run down. Should be given to me to make into an international centre of pinhole photography!