Aperture settings

As modern electronic cameras become increasingly sophisticated, it could be argued that the need to understand the basics of photography is no longer necessary. While accepting that today’s automated cameras are capable of doing most of the basics, it is worthwhile trying to master the underlying principles if you are to progress further than the ‘point and shoot’ stage.

There are only four components in a technically-correct photograph – focus, shutter speed, aperture and film speed. Correct focus is easy if you have a reflex camera. You look through the lens and adjust it until the subject is in focus. With non-reflex cameras such as Nikonos and Sea & Sea you must estimate the distance from lens to subject and set the lens accordingly. Practice will improve your success rate but, as we saw in last month’s article, framers with close-up devices and wide depth of field with wide-angle lenses makes focus estimation much less of a problem than it first appears.

The final three components all have an effect on each other. Shutter speed is the length of time the shutter is open – the longer the time, the more light reaches the film, and vice versa. The same is true for aperture (the hole in the middle of the lens) – the wider open it is, the more light reaches the film and vice versa. Film speed follows the same basic principle – the faster the film (400 ISO is faster than 50 ISO, for example), the less the amount of light needed for a correct exposure.

Consider the following situation – you are a farmer with ten sheep which you want to get from one field to another. If you only have a gate which will allow one sheep to pass at a time, it will take ten times longer than if you had a wider gate, through which all of the sheep could pass at once. The gate is your aperture and the time taken is your shutter speed. The result is the total exposure. My best explanation of film speed in this scenario is either a stick or a sheepdog to make the sheep go faster, but we’ll come back to that later. If I can now drag you back from the farm to photography, typically-used shutter speeds are quoted in fractions of a second. For example, 1/60th of a second will let twice as much light through as 1/125th of a second.

The most widely-used shutter speeds are 1/30th, 1/60th, 1/125th, 1/250th and 1/500th, but with today’s cameras this can be extended to the extremes of 30 seconds to 1/800th of a second.

A long shutter speed (longer than about 1/60th of a second) will mean you have to hold the camera much steadier for a sharp result. If you shorten the shutter speed to avoid this, you will have to compensate by opening up the aperture to let in more light.

Apertures aren’t quite so logical (and could really do with metrification) but, if you really want to know, the number of the aperture is the effective diameter of the aperture divided into the focal length of the lens. You don’t need to remember that, except that it results in some rather odd numbers which typically range from f2.8, 4, 5.6, 8, 11, 16 and 22. The important thing is that, like shutter speeds, there is a logical progression/relationship – the area of the aperture at f2.8 is twice as wide as f4 and so lets through twice the amount of light.

The problem with opening up the aperture to let in more light is that it will make the focus more critical. The wider you open up the aperture, the more the light refracts, giving you less depth of field (making the image less sharp overall). If the aperture is kept small, the light entering the camera has less chance to refract so you have a greater depth of field – a larger area will be in focus.

So, for every advantage there is an equal and opposite disadvantage. If you are in a lighting situation where your aperture is already fully open, you could use a faster film to enable you to use a faster shutter speed (the stick or sheepdog mentioned earlier). The disadvantage of this is that the faster the film you use, the more grainy and less colourful the results will be.

This is a lot of information to take in but it is well worth taking time to understand the relationships between these three basic components. If my explanation has baffled you (heaven forbid), look at some of the books on underwater photography which explain these basics in their own style.

I will leave you with the often quoted answer to ‘What’s the secret of underwater photography?’ Simply ‘f8 and be there’.

• Next month: How to get the best photographs out of British waters

Pics win prizes!

Maldives Scuba Tours will be running two new photographic safaris on the liveaboard MV Sea Queen, with Michael Aw and Linda Dunk hosting photographic workshops. There will be prizes for the best photographs – including photographic equipment, books and travel vouchers. The winning shots will be published in future issues of DIVE. The price is £1,965 per person, including flights (Emirate Airlines), full board, diving, workshops, and four free films, including processing. The safari dates are 15–19 August ’99 with Michael Aw, and 23 January–6 February 2000 with Linda Dunk. Phone Maldives Scuba Tours: 01449 780220 or e-mail info@mst.keme.co.uk