Simply – ‘A light meter is an instrument that measures the amount (or intensity) of light!’
From browsing through the two books stated above by Micheal freeman I have learnt that there are a few different methods of light metering functions that a DSLR has.
(Here is a photo of the Light reading metre on my Nikon d5100 which is also present when looking through the view finder)
1) SPOT METERING – This type of metering always you to take a reading of the light from a small central area in the camera, this is often shown as a dot in the centre of the viewfinder which measure about 2% of the image area. This type of metering is often used when focusing on the tonal value of a image.
The above diagram demonstrate the spot metering concept, to the left the diagram is demonstrated from a books perspective and the image to the right is a diagram that I have created that demonstrates the spot metering concept from altering the settings in my Nikon D5100 and peering through the viewfinder to see the change in shooting screen.
As we can see from the diagram on the right hand side the way the Nikon D5100 spot metering setting works is that it creates almost a template within the viewfinder. This template is a guidance for photographer, when gently pressing down the shooting button (without fully pressing to take a image) a couple of the circles within the template grid light up in red showing the reading of the 2% of the image that the lens is focusing on, this determines that this particular area will be of greater focus and exposure once the image has been taken.
(A photograph of me successfully locating the spot metering setting on my Nikon D5100)
2) CENTRE WEIGHTED METERING – This is almost the ‘standard’ type of metering, this type of metering gives priority to the centre of the screen thus assuming that the image is composed in centre which is not always necessarily true. With this type of metering less attention is paid to the edges of the frame, again assuming the main focus is composed in the centre of the image.
3) MATRIX/ MULTIPLE PATTERN METERING – This is almost like a auto default for high end cameras, in simple terms the matrix records a average of light in the areas of images, the matrix then shows the the areas of high tonal value and low tonal value within the matrix.
4) CENTRE-CIRCLE METERING – This is similar to centre-weighted metering however it is more relevant to use it with macro shots i.e. shots that are close up. This type of metering is deal when applying the ‘Rule of thirds’ framing method.
WHAT HAS BEEN LEARNT THROUGH METERING
The main learnings through looking into metering would be that the what is perceived as the ‘correct exposure’ is down to subjective preference. The use of the different metering methods are dependent on the subject that is being photographed, applying the correct metering method will create a ‘better’ or more relevant exposure of light within the image thus leaving a better outcome.