As mentioned in a previous article, photography originated from the world of art, and the first version of the camera, the camera obscura was nothing more than an artists’ tool. If you are the kind who likes DIY projects, we’ve put down a few tips on how you can make yourself a camera obscura.

What you’d need –

1. A Lens
2. A Light Tight Box
3. Ground Glass

If you feel that these materials may be hard to come by, do read on and we’ll explain how you can improvise.

The Lens needn’t be an expensive one from a camera. Something as simple as a cheap magnifying glass would do fine for our project. The light tight box could be a firm shoe box (cardboard is easy to cut into so that’s a good idea). Ground Glass is a semi transparent sheet in the absence of which you can use butter paper. Even a semi transparent plastic sheet would work fine.

So, the camera obscura is nothing but a light tight box with a lens fixed on one plane having a projection screen on the opposite plane. Find the approximate centre of a convenient plane on the box (you can do so by making lines from opposite corners – the criss-cross intersection is obviously the centre). Cut out a hole just a little smaller than the diameter of the lens and fix the lens on the inner side of the box using scotch tape.

We need to cut out the opposite plane of the box now. An important point to remember is that a lens forms an image of a distant object (we call it infinity), at a lens-screen distance that varies with the lens model. This distance is referred to as the focal length of the lens. Determine the focal length of your lens by  -

1. Darken the room
2. Light a bulb/candle at a good distance from the camera obscura
3. Move a piece of paper towards and away from the lens, on the inner side of the box. At one point the image of the light source appears the sharpest (yes the image is always inverted and mirrored). Mark that point. The distance from this point to the lens would be the focal length of the lens.

Once you know the focal length, affix the ground glass/paper/plastic screen to that distance from the lens, and you have your camera obscura model ready! There is a whole lot that you can learn about the basics of photography from this simple device –

1. You could fix the lens to a plastic tube that slides in and out of the box – this is how a camera ‘focuses’. See the difference in lens-screen distance, with near-by subjects and subjects that are far away.
2. Covering the sides of the box from the rear as you view your screen makes the image look brighter – this is why light-tightness is important in a camera. Light leak can cause ‘fogging’.
3. Cover the outer few millimetres of circumference on the lens with a paper ring. The image becomes fainter of course, but look carefully and you see more subjects coming into ‘focus’ and this is better observed by focusing on an object only a couple of feet away. This gives you a good idea of how aperture (the diameter of lens that is uncovered by paper) and the effect it has on depth of field. More on depth of field later...