Wandering around the Theatre & Circus field at Glastonbury Festival, a little round tent catches my eye. It’s tiny – far too small for any kind of exhibition or performer.  The deliberately old-fashioned signs outside proclaim ‘Willett’s Amazing Camera Obscura’  ‘A Scientific Marvel’  ‘A Wonder of Nature’. People are going inside in small groups and emerging a few minutes later with surprised-but-happy expressions on their faces. I am intrigued.

The friendly man on the door won’t tell me what it’s all about - “Its best if you see it for yourself "– so I join the short queue outside.

Look up ‘camera obscura’ and you’ll find it’s Latin for ‘dark chamber’ (not ‘dark camera’ as you might have expected). You will learn it’s a way of using the scientific properties of light to project an upside-down image on to the wall of a dark room (or box) by letting a pinhole of light capture whatever is outside the opposite wall or side. It was a popular form of public entertainment in Victorian times, but the technique has reportedly been known since 500 BC. It was used by early astronomers to observe the sun without damaging their eyes.

In the 1550s the pinhole was replaced by a lens, which produced a brighter image but the picture needed focusing. This was achieved by moving the viewing surface or the lens.

But that doesn’t really give me a picture (double meaning intended) of what will happen inside the tent.

Time to find out. With five other people, I go in, and we find ourselves standing in a small dark room around a circular white table which is acting as a screen for what looks like a blurred video film of the field outside. On the table are a few thin white circular plates that we can pick up – and when we do so, something ‘amazing’ happens. On the plate, the image comes into focus and we can clearly see some of the people standing outside the tent – who have no idea they are being viewed from inside. When we move the plates further from our eyes,  the image gets sharper. It’s like a secret video camera, and it’s good fun. Some of the people in the tent go outside to see if their friends can pick them up on the camera obscura.

(Image: Philippa Davies)

The way this has been done is with a lens mounted horizontally in the roof of the tent, and a mirror at 45 degrees placed above it, so that the image in the mirror is beamed on to the table. Lifting the plates brings the image into focus.

This must have been a truly scientific marvel in the days long  before photography, let along video, was possible. And I can't help thinking it could have potential uses today. With limited police resources, could it be used instead of security cameras in some locations? It may not capture images, but a sign saying 'Smile! You're on our camera obscura' might deter shoplifters. 

As Glastonbury Festival experiences go, this wasn’t particularly spectacular, awe-inspiring or ‘big’. But it was fascinating and quirky and very charming in its way, and I wouldn’t have missed it for anything.