Do It Yourself
Nowadays, even the cheapest mobile phones come with a camera - but before digital, how were images obtained, stored and developed? Have a go at making your own camera and taking some snaps. Not only will you learn about the process, but it will teach you to appreciate how simple point-and-shoot cameras work!
Most cameras have four main components:
- a box to protect the film from light other than that entering through the lens;
- a lens, to gather the light rays from the object and project them onto the film, so creating a focused image. To do this there must be some way of moving the film (or the lens) backwards and forwards;
- light-sensitive film, on which the image is recorded; and
- a device for controlling the amount of light passing through the lens, consisting of an adjustable aperture (iris) and shutter.
The simplest camera uses a tiny hole as a lens. Light falling on such a ‘pinhole’ emerges on the other side and creates an image on a screen some distance from the hole. For a sharp image, the hole needs to be very small. This means that only a small amount of light will be let through, so the image that’s formed will be dim. We considered using a pinhole for the ‘lens’ on the castaway camera, but decided that there wouldn’t be enough light.
A simple camera compared with the human eye
The Castaway camera
The castaway camera consists of a wooden box (approx 45 x 30 x 30cm), with one of its four large faces missing. The box, which should have a 1cm hole drilled in its top face, contains a moveable screen, underneath which sits a mirror. A second mirror is mounted on top of the box. Both mirrors should be inclined at 45 degrees.
Light from the object to be photographed is reflected by the upper mirror down through a lens placed over the hole in the top. The lens concentrates the light onto the screen, where it forms an image. It helps if the upper mirror can be rotated, so that light from different objects can be directed into the box – a bit like a periscope.
Wandering around the prison site on Capraia, we found a rubbish dump with some pieces of broken glass bottles. We were amazed to find that when placed over the hole in the top face of the box, the bottle bottoms actually acted as lenses. You could experiment with different lenses; try spectacles or a magnifying glass.
bottle-bottom lens with rotating mirror in its housing
The screen is just a piece of tracing paper mounted on a moveable wooden frame. To focus the camera, the screen is moved up and down (in other words, nearer to and further away from the lens) until the image is as sharp as you can get it. Of course, it helps if the subject to be photographed is as still as possible.
Some light passes through the screen onto the lower mirror, which allows you to look at the image from a comfortable angle through the open side of the camera. This open side should be covered with two or three black bin-liner bags to keep the light out and to allow the operator in.
On Capraia, we used a mud paste to plug any holes in the box and thus prevent stray light entering – the only light you want in the box is that coming through the lens. As a final touch, we built a simple tripod to support the camera while we were ‘out on location’.
Having positioned the camera so that a high-contrast image was visible on the screen, we focused the image and placed the home-made photographic paper on top of the screen. Unfortunately, our castaway film was very insensitive and even after about 30 minutes’ exposure (in late-afternoon sunshine) no discernible image formed on it.
This is hardly surprising. We really needed to treat our castaway ‘film’ with a developer, as we would if we were using proper photographic film; the developer enhances the initial image that forms on the film. We also needed much longer exposure times than we had available at the end of this particular three-day challenge.
- Mounting the film in your castaway camera is perhaps the trickiest part, as it needs to be done with a great deal of care. We suggest that you use standard photographic film (say, 200 ASA) and that you only reveal something like 5cm sections of it at a time.
- Do bear in mind that shop-bought film is much more sensitive than our castaway film, so try out various exposures, from one second to ten seconds in half-second steps, and then from ten to 60 seconds in five-second steps.
- Also vary the size of the camera’s aperture by placing different sized cut-out holes underneath the lens – from a pinhole to one that’s 0.5cm in diameter.
- As you expose the film, roll up the used part and cover it with something light-proof. This is really fiddly and requires a lot of patience. Once all the film has been exposed, roll it back into its canister and get it developed – you’ll need to warn the developer that some of your photos might not be very good!
Book 4 of ST240, Our Chemical Environment
Book 6 of S207, The Physical World
Units 1 & 2 of ST291, Images and Information
Rigos A.A. and Salemme K., Photochemistry and Pinhole Photography, Journal of Chemical Education, vol. 76 (6), pp. 736 and 736B, 1999.
FURTHER GENERAL READING
Here are some books and articles that you may want to try and get hold of:
Barrow J. D., The Artful Universe, Oxford University Press
A quite remarkable book that will change the way you view the world. Extremely accessible.
Burton et al., Chemical Storylines, G. Heinemann Educational Publishers
Part of the Salters Advanced Chemistry course, which explores the frontiers of research and the applications of contemporary chemistry. For A level and other science courses aimed at 16 to 19-year olds.
Fraser A. and Gilchrist I., Starting Science (Book 1), Oxford University Press
Part of an integrated science course for the National Curriculum Key Stage 3 and Scottish Environmental Studies (science) for S1 and S2.
Northedge A. et al., The Sciences Good Study Guide, The Open University
Indispensable for students of science, technology, mathematics and engineering. Packed with practical exercises and activities, all aimed at making studying more enjoyable and rewarding. Lots of hints and tips for those returning to study.
Selinger B., Chemistry in the Marketplace, 5th edn., Harcourt Brace
An excellent and informative reference source for all kinds of real-life applications of chemistry. Explores the world of chemistry that surrounds us in our daily lives, explained in terms that everyone can understand. ‘Makes chemistry come alive.’
PS547 Chemistry for Science Teachers course materials, The Open University
A course designed for use by science teachers from a wide variety of backgrounds, with varying experience of teaching science. A familiarity with some basic science (perhaps physics or biology) is assumed, but little understanding of chemistry is required. The mathematical understanding needed for the course is not great.