Although we see it generally as a white light, it consists of a range of different colors (and frequencies) with a varied intensity depending on season and time of day. Without a minimum of available light it would be impossible to capture a quality image of our subject.
Before we attempt to capture our image there are a number of factors we need to consider:
1) The detector in our camera records the reflected light from the subject.
2) The direction of the light is an important consideration and may come from behind the subject, from either side or from behind the photographer. Clearly the choice here will effect and / or change the final result.
3) The intensity or amount of light that passes through our lens on its way to the detector can be controlled (and should be) by two main features.
3a) Aperture Settings (A). This is an important setting and is lens dependent. The smaller the f stop results in a larger aperture and allows the passage of more light and the opposite applies, i.e. the larger the f stop number will result in less light (and a greater depth of focus).
3b) Shutter Speeds (S). The shutter speed is another important variable. Shutter speeds vary from camera to camera but can range from a few seconds to speeds up to 1/4000 of a second or faster. Generally speaking we select this feature when we want to capture fast moving subjects.
A general rule worth remembering is the 'reciprocal rule' where the shutter speed equals the inverse of the
focal lens currently used. In short, S = 1 / focal length. If one is using a prime 50 mm lens then the shutter speed should not be less than 1 / 50 of a second. Using a tele lens at 250 mm the shutter speed should not be less than 1 / 250 of a second. The use of a tripod is an alternative solution!
4) The sensitivity of our detector. This setting is called the ‘ISO’ or ‘ASA’. When there is insufficient light we can raise the sensitivity from say 100 ASA to perhaps 400 ASA or even higher if necessary.
5) If we decide to give priority to our aperture setting, the built-in light meter in our camera will automatically adjust the shutter speed to provide the ‘right’ amount of light to the detector. Alternatively, if we first set the shutter speed, the aperture will be adjusted to provide the light required as measured by the light meter.
6) Light Meter. This important built-in device is critical in obtaining the right exposure of our images and can be adjusted / aligned or calibrated if necessary. Here we also have a degree of control as to how and where we measure the light intensity. The 3 major options are a) matrix where the light reading is taken over a number of different points in the viewfinder frame and averaged, b) centered weighted (about 65%) is given to the reading at the center of the frame. This tends to be a favorite choice particularly if the subject takes up a large part of the frame and c) spot metering. This light reading is about 1% - 3% around the recording area and gives an accurate reading at a specific point. This option is usually used by advanced / experienced photographers.
7) White Balance (WB). Another problem we face is the fact that our light is not always a pure white color! The results of photographing the same subject in sunlight, overcast weather, under tungsten or fluorescent lamps and / or with the use of a flash will differ considerably. In many cases the ‘auto’ option will suffice but for better results the WB settings can and perhaps should be changed according to the type of light encountered.
8) Flash. In many case where there is insufficient light reflected from the subject, an artificial source of light maybe required. Most cameras have a small built in flash effective from 1 – 3 meters from the subject and referred to as a ‘fill-in flash’. The use of this flash is recommended for faces in shadows and foregrounds in shade. Where a more powerful flash is required a variety of options are available provided the camera has a ‘hot shoe’ mounted on top of the camera. The choice will probably be both budget and subject dependent. In most cases the flash ‘talks’ to the camera and both are in synchronization with the shutter speed usually set at 1/125 or 1/250 of a second. The output or intensity of the external flash is provided as a ‘Guide Number’. Additional points to watch when using a flash include the ‘red eye’ problem of people looking at the camera when photographed and background obstacles of mirrors and windows that reflect the light.
The understanding of how the use of light relates to the quality of our images is critical to our progress in becoming successful photographers and is one of our major challenges! Experimenting may well help you meet this challenge!
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