Understanding and Using the Camera Light Meter
If you want to take properly exposed photos, it is important to understand how your digital camera’s light meter works. The camera’s aperture, shutter speed, and ISO speed are controlled by the metering system. It also depends on the lighting conditions and the ISO speed. Metering can be done in spot, evaluative or matrix mode, partial, centre-weighted, and full metering. Each of these metering options has lighting conditions they excel in as well as those that they fail to do so. Understanding these options will improve your final results.
Incident and Reflected Light
Since reflected light is all they can measure, cameras’ light meters are imperfect from the beginning. The camera must calculate how much light is actually shining on the subject. It wouldn’t be a problem if each object reflected exactly the same amount of light. All objects reflect different amounts of light. Camera light meters have been standardized because they measure how much light a grey object would reflect. If the camera is pointed at an object that is darker or lighter than this shade, the meter cannot calculate the amount of light being reflected. This will lead to images that are either over or underexposed.
The reflection of incident sunlight in middle grey is usually 18%. However, most cameras calculate it to be between 10-18%. The exposure may be off if the object in an image reflects less light or more. Even though the photo may have both dark and light objects, the average amount of reflected light could still fall within the camera’s grey range. It may be difficult to get the right exposure if your image shows a black cat on a rug or with a white object in snow.
There are many options for metering.
You can meter different parts of the scene to get properly exposed photos for a variety of reflectance and lighting options. Exposure calculation is most effective for the whitest areas of a scene. Black sections are generally ignored. Calculating the reflected light for each section of the image is the best way to measure it. This allows you to divide the scene into sections and calculate the amount of light required for each section.
Spot and partial metering
You can choose the area of the image that you want to measure with these types of metering. It takes some practice to become comfortable with them. It is possible to use partial metering when photographing someone who is backlit. It will ensure that they don’t appear too dark or underexposed when taking photos of them. It might not work if the person’s skin colour is different from middle grey. Spot metering can be used to measure a specific area or a part of a scene.
Exposure compensation and centre-weighted metered metering
As a default setting for a camera, centre-weighted meters were quite common. These days, matrix and evaluation are more popular, particularly spot and partial metering. While centre-weighted meters will give predictable results, matrix and evaluative modes use complex algorithms that make it more difficult to predict.
Exposure compensation can be used with any mode of light metering. If your photos are consistently under or overexposed, you can adjust the settings. If you don’t manually adjust the exposure compensation to plus 1, the white object in snow will cause an underexposed shot.