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 light, achieved by simply blacking out a window and using a +1 diopter close up filter to project an image of the outside world onto a hanging sheet.

Assembly.

Find a room that can be blacked out. Ideally with a view to the North (in the Northern hemisphere) so the window doesn't look into the sun. 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.

Using a Lens.

Many people try to project onto a wall, the disadvantage with this is as, we all know, lenses have that nasty quality of having to be focussed. Better to get a lens and hang a sheet at its focussing point. This can then be rolled up and attached onto the celing.

Image projected on to a sheet (which needed ironing!)

Lens positioned on window blackout

A +1 Diopter close up lens (easy to find for a few pounds on the web) will focus at around 4 foot, if a thin white tablecloth - sheet is then placed at this point it can be viewed 'through' the sheet, as well as seeing it by moving twixt window and sheet (fine for one person, a bit cosy for a class of 30!)
You can then get someone to jump around outside or write 'This is upside down and back to front' on a board.
(so it appears the right way round).

Using a Pinhole.

A pinhole positioned a few cm above the lens, (the size of a hole punch) will also be fun, allowing you to skew the projection of the outside world etc.

Cut out a 3cm area in the blind and replace it with a square of aluminium with a hole punched through using a paper hole punch. Not a good on cloudy days for mass viewing but good for various experiments, ie why is the sun still round through a square hole? Good old Aristotle!

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 shutter - 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.

View PowerPoint
(works better viewed in IE i'm afraid!)

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!
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