Integrated reflected light meters are part of all new DSLR cameras and work in the same way as hand held reflective light meters. When you look through the view finder, the display of information helps identify the way in which your camera is calculating the light.
As there are different in camera metering systems it is best to consult your manual to understand the different ways in which your camera meters light or experiment with the different modes.
Some common metering modes are:
Centre Weighted - Calculates the middle grey between the highlights and deep shadows (usually great for landscapes)
Spot Metering - The light meter selects a small part of the scene (2.5%) as the basis for its exposure (usually great for portraits)
Partial Metering - Like spot metering, but takes a larger portion of the scene for the calculation (6.5% instead of 2.5%)
Evaluated Metering - Takes multiple readings from one scene/zone and calculates the average based on this selection
Chose two of your favourite metering modes (personally I like Evaluated and spot metering all depending on what I'm doing) and have a play to see which ones are best suited to your style of photography.
18% Grey Card
All modern cameras have a built in reflective light meter, which helps the camera determine the correct exposure settings from the amount of light bouncing off a scene. The subjects we decide to photograph, whether it is portraiture, landscapes, objects or animals all give off a different reflective light.
For this in camera system to work, the reflective light meter makes certain assumptions and will provide for an average amount of light in the scene (between the highlights and the deepest shadows) known in the trade as "Middle grey".
In other words, cameras assume that each scene contains an even distribution of light and will set the same tonal value as middle grey. If however, the scene is not middle grey we end up for an under or over exposed image (think of a snow scene or a night time shot). To ensure that a properly exposed image is captured, a grey card is used.
A grey card is literally a piece of cardboard that is specifically 18% grey reflected across the visible spectrum.
To use a grey card , place it in the area of the shot you wish to take and approximate the angle of the light falling upon the subject. Then, fill the cameras view finder with the grey card and see what exposure settings you camera recommends. These recommendations present an accurate average reading and will be displayed in the view finder.
If you find yourself without a grey card, a neat trick is to use the palm of your hand and then increase the exposure one stop.
My next post will cover the Kelvin scale and Custom White Balancing.