The Probert Encyclopaedia of Science & Technology

PHOTOGRAPHY

Photography is the art, and sometimes business, of taking and also sometimes producing and printing photographs.

Early cameras operated upon the principle of allowing light reflected from a subject to fall upon a light-sensitive chemical impregnated plate, later plastic film. These plates or films were then treated with other chemicals to prevent further sensitivity to light, thereby fixing the image which was then printed. Later digital cameras evolved which used electronic light sensors to record the image in a binary digital file on a memory card.

If too much light is allowed in to the camera, the picture will be over exposed, and will look bright and indistinct. If not enough light is allowed in, the picture will be under exposed and will look dark and indistinct. It is less common for photographs to be over exposed, than under exposed.

Light is allowed in to the camera to the photograph plate, film or sensor through a quickly opening and closing door called the shutter. The size of the hole which is revealed by the shutter is known as the aperture, and is measured in F-Stops, such as F1.8, F4.5, F11 etc. Where, confusingly, the larger the F number the smaller the aperture is. Thus, F1.8 is quite a large aperture, and F11 is fairly small. A larger aperture, represented by a smaller F number, lets in more light than a smaller aperture.

The length of time for which the shutter remains open, letting light in through the aperture is often referred to as the shutter speed, and is measured in fractions of a second. Thus, a shutter speed of 500 implies that the aperture will be open for 1/500th of a second, while a shutter speed of 125 implies that the aperture will be open for 1/125th of a second. The longer the aperture remains open, the more light will enter.

How quickly the photographic plate, film or sensor reacts to the light reaching it through the aperture is known as the sensitivity of the plate, film or sensor and is measured in ISO or ASA units. The larger the ISO value, the quicker the plate, film or sensor will react to the light. Thus, a sensitivity of ASA or ISO 100 will react slower than a sensitivity of 200 or 400.

The aperture size, shutter speed and sensitivity, work together to determine the level of exposure that occurs when a picture is taken. Automatic camera settings will set these three values for you, so that the picture is properly exposed, and if it can not be properly exposed, will warn you. However, there are other effects connected with each of these three settings.

The higher the sensitivity of the photographic plate, film or sensor, the more grainy or noisy the photograph will be. Therefore, using the lowest possible sensitivity will give the best possible quality for the photograph. In order to use a low sensitivity, the subject must be as brightly lit as possible. For example a subject in bright sunshine or lit by powerful lamps or the use of a camera flash gun.

The camera's aperture size governs the depth of the photograph. The smaller the aperture is, the deeper the field of focus. Using a large aperture size will result in only the subject being in focus, objects behind and in front of the subject will be blurred. Using a small aperture will allow objects behind and in front of the subject to also be in focus. The smaller the aperture size, the further behind and in front of the subject objects will remain in focus, and by extension the easier it will be to focus upon the subject.

The most noticeable effect of the shutter speed is in reducing motion blur and camera shake. When holding a camera, particularly one with a long lens every one will quiver their hand to a greater or lesser degree. When using a zoom lens, this quivering or camera shake is much more noticeable than when using a shorter or wider angle lens. If the camera is moved, even slightly while the shutter is open, the picture will be blurred. The more the camera moves while the shutter is open, the more blurring will occur. By using a fast shutter speed, the shutter is open for less time and as such less movement affect the photograph. Similarly, if the subject being photographed moves while the image is being taken, the resulting photograph will be blurred. Using a fast shutter speed of 1/500th of a second or faster enables photographs to be taken of action shots, such as footballers in mid-movement or in the air while heading the ball. The subject's movement being slower than the speed of the shutter opening and closing which appears to freeze the moment in time.

The best way to reduce camera shake is to use a tripod. If you can not use a tripod, try resting the camera on a firm surface, such as a wall, fence post or tree. It can not be over emphasised that using a tripod will result in better photographs as every one quivers ever so slightly when taking photographs. Even activating the shutter release on the camera can slightly jar the camera. To overcome this, many photographers use a camera with automatic frame advance or sequential shooting, whereby after activating the shutter release the camera takes multiple photographs until the shutter release mechanism is released. In this way, three images may be taken automatically, the first and last will often suffer from slight camera shake due to the action of operating the shutter release mechanism, while the second image will not.
Research Photography