Tech Biz Writing

Photography:
This section covers only the basics of photography and doesn’t deal specifically with digital cameras which are almost universal now. To find how-to articles on digital photography, see our blog: Digital Camera Latest.

We will assume that all photographs to be used in illustrating a handbook will be taken professionally. This is not to say that many writers are not also effective photographers, but generally their time is spent more efficiently in attending to writing tasks. There are times, however, when an author will be called upon to photograph equipment for information purposes, or to supply an illustrator with the basis for line drawings.

Consequently, a useful addition to any writer’s baggage train is a good quality 35mm camera — SLR or compact. It should be capable of focusing down to about 18in, and have a maximum aperture of at least f/1.8 — factory storerooms can be surprisingly dark areas. If you are an experienced photographer, skip the following section. If not, it may give you some background knowledge on which to build.

Photography in a technical age has largely been reduced to pressing buttons on highly automated optical recorders. Most new cameras are fully, or partially, automatic, and very little choice is left to the operator. Apart from focusing, the photographer has only to make a choice of either shutter speed (in a shutter-priority model — good for fast-moving subjects), or aperture (in an aperture-priority instrument — good for dark places).

A light reading for a shot is expressed as a trade-off between two associated parameters:

* f/stop — the ratio of lens focal length (on infinity) and the diameter of the lens aperture.
* Shutter speed — the time, expressed as a fraction of a second, for which the shutter remain open.

For a given light intensity, opening the aperture wider (say from f/5.6 to f/4) will require a corresponding decrease in shutter speed (say, from 1/125th sec. to 1/250th sec.). The difference between f/4 and f/5.6 is said to be one f/stop, in that f/4 allows twice as much light to pass through the lens in any given period of time as f/5.6. Therefore, by halving the time for which the shutter is open, the correct exposure is restored.

For example, the following combinations all represent the same exposure onto the film:

f/1.4 1/1000
f/2 1/500
f/2.8 1/250
f/4 1/125
f/5.6 1/60
f/8 1/30
f/11 1/15
f/16 1/8

The most appropriate choice between these eight combinations will depend on the situation to be photographed. A shutter speed should always be selected in relation to the subject and its capacity for movement within the field of the shot. For example, a handheld photograph will probably exhibit camera-shake at shutter speeds of 1/30 or lower. Heavy drinkers should uprate that speed! For speeds lower than 1/60, a tripod or firm surface is essential.

In choosing the shutter speed the movement of the subject is the deciding factor. A low-flying jet aircraft will require at least 1/500th and, ideally, 1/1000th of a second, even when panning with the subject. A stationary vehicle, on the other hand, may be shot handheld at speeds as low as 1/30th, and at any speed on a tripod.

The aperture of the lens at the time of shooting presents another problem of choice. Apart from considerations of light, the wider the aperture, the smaller the depth of field. This means that with the lens focused on a specific object, the range of tolerable definition extending before and beyond the subject, increases as the aperture is decreased. At full aperture, say f/1.8, very little depth of field is available. This may be useful for eliminating unwanted or fussy backgrounds, but it’s not so welcome when shooting subjects which extend considerably in distance and which must be sharp overall. The only solution may be to move it to a lighter spot, or bring in artificial lighting so that the aperture can be closed a little.

At f/22, the depth of field on a standard lens is such that if the lens is set at 10-15 feet, almost everything from about 6ft to infinity will appear acceptably sharp. Cameras nowadays do come in fully automatic form, but for most technical work it is felt that some choice should be left to the operator.

Next: 24. The Synopsis.

This entry was posted on Sunday, June 4th, 2006 at 3:30 pm and is filed under Technical Writing, TechBiz Writing, Documentation, Design, Research, Photography, Digital Cameras. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.