By Eugene Struthers
The exposure setting is calculated based on the data from the matrix/ segment elements (3 to 16 or more), dividing up the scene into segments and taking readings from each segment, then analysing the results to determine the optimum exposure. This will also depend on certain circumstances such as the following factors:- the focusing point in use, subject size, subject position, distance, the total light levels in front of and behind the subject, colour level densities. Ideally use this mode when your subject is without large shadow or extreme bright areas:- Action photography. The advantages:- You will achieve good reliability in your images. Problem area's:- You will have no control of the exposure settings. You will not know how the camera weights the elements. Multi-segmented metering (Evaluative/ matrix):- Mode takes a number of light readings from different parts of the frame (dark and light elements) then combines them to create a balanced exposure. In this mode, the camera uses automatic scene recognition to analyze the subject and provide optimum exposure in a wide range of shooting conditions.This mode should be used for everyday photography.
The metering is averaged over the entire scene with emphasis placed on the center area (about 75% center marked dark grey and black in the icon and 25%) outside.Use this mode when your main subject covers a large portion of your image, when there is peripheral shadows. The centre weighted average works by taking an average reading from the entire frame, with an emphasis on the central 40%-60%. Functions efficiently under average lighting conditions, but is easily manipulated by bright or dark areas.This light metering reading is calculated using a fixed algorithm, and is easy to predict when it will fail. This mode is ideal for portraits.Advantage:- the metering mode for general scenes with relatively easy exposure compensation control. Centre-weighted metering:- This reads light in the centre of the frame, feathering or fading out towards the edges. The average of this mode is that the exposure tends not to change for different compositions or subjects. This mode is particularly effective for shots of people wearing black or white clothing and shots of scenery.
This mode takes a light reading from a very small area of the frame allowing you to obtain a very precise light reading. Use this mode when there is a large difference in brightness between the foreground and background or for subjects that require precise measurement, such as closeup photography. Advantage:- A precise metering in your control.Problem:- Heavy variations in metering results. Bracketing will need to be applied for very extreme situations. Spot Metering:- This is potentially the most accurate metering mode, as it enables you to take a reading from a tiny area just 1-3 % of the frame. This mode however, requires a high level of skill, as you will be required to identify the subject areas that represent suitable mid-tones.This mode is useful for subjects with strongly contrasting light and dark areas where you want to achieve the correct exposure for a particular feature. To achieve this meter off a grey card placed next to the subject.
This mode meters a larger area than spot metering (about 10-15% of the entire frame) and is generally used when a bright or very dark area on the edges of a frame would otherwise influence the metering greater than is reasonable. The setting is useful when your subject is strongly or overly backlit. The metering is weighted towards the centre of the viewfinder covering approximately 13.5% of the area. Like spot metering, some cameras can use variable points to take readings from, general autofocus points, or have a fixed point in the centre of the viewfinder. This type of metering is mostly found in Canon cameras. Partial metering:-this mode is also known as "Selective area metering" due to the larger diameter (7%-9%) that it occupies compared to the Spot, which is only 3% or less. Unlike the "Evaluative metering", the Partial mode with its 9% sensitivity area at the center of the viewfinder, makes it easy to verify that the camera is measuring the exposure values.The Partial metering area is larger than the Spot meter, the desired portion of a scene can be metered and the auto exposure reading locked via the AE lock button. This will enable fast AE picture shooting with the desired effect. Partial metering pattern is most effective when the precise exposure of the subject or a certain area of the frame is desired for example:- strong contrast between light & shadow, strong backlit subjects, such as a scenery with a bright sky. It is also very effective for AE photography and in close-up applications.