A photograph records the light reflected off of the subject on the sensor in the camera. To get a properly exposed photograph, the camera needs to record enough of the light so that there is detail in the dark and light areas, without being too dark or too light. The first step is to know how much light is actually present in the scene. To do this, you need to measure it.
Exposure settings are covered in detail in Chapter 6.
A light meter is used to measure the brightness of the light present in a scene. All light meters work in the same general way. They convert the amount of light in a scene into a measurable form, and then convert that information into a form that the camera and photographer can use. There are two types of light meters: Direct (or Incident) light meters measure the light falling on the subject, and Reflected light meters measure the light that is bounced from the subject. The Nikon D3200 has a built-in light meter that reads the light reflected off of the subject and coming in through the lens, so it can accurately determine the amount of light reaching the sensor. As the light in front of the lens changes, the built-in light meter updates.
In the past, photographers used a separate, handheld light meter, took the settings, and then entered them into the camera. There are times when this is still a good idea, especially when working in a studio. The light meters shown in Figure 5.14 can be used to trigger studio strobes ...