How to Understand Your Camera’s Light Meter and Get the Exposure You want

Regardless of how you shoot, and whichever shooting mode you prefer to use, there is one item that remains constant – the light meter. Somehow, either you or your camera has to know how much light in on your scene in order to determine the optimal combination of aperture size, shutter speed, and ISO sensitivity to get the photo you want. This tool, which may not seem all that relevant to new photographers, is called a light meter.

Understanding what your camera’s light meter does and how it works is critical to advancing your skills and helping you get the shots you really want. Hopefully, this article will help you get a grip on it.

Before I get into a discussion about how the light meter works, think about the last time you cooked some meat on the grill. Whether it was a steak, some pork chops, or even just a couple hamburgers – you likely had a vision in your mind of what the finished product would be.

For backyard chefs like me who aren’t very good at this sort of thing, we have to use a meat thermometer to make sure our food is properly cooked. There’s always the question of where to put the thermometer to check and see if the meat is done. Or, in photography terms, check to see if the meat is properly exposed. You can touch it to the surface, poke it through to the middle, or insert the thermometer at various points around your dinner in order to get a good overall reading.

How the camera light meter works

When you point your camera at a scene you also need a way of measuring the incoming light so you know how much of it there is and what settings you (or your camera) need to control in order to get the shot you want. It’s just like measuring the temperature of your food with a thermometer to make sure it’s done properly.

Most cameras today use a process called TTL Metering, which stands for through-the-lens. It means that your camera examines the light coming in through the lens and evaluates the brightness of the scene. Then you, or your camera, can adjust the settings in order to make sure your photo is exposed how you want. You may not ever notice the light meter at work or even see that it’s there at all unless you shoot in Manual Mode. But trust me, it’s constantly monitoring the light whether you know it’s working or not.

Measuring the Light

Most cameras today have a few basic ways of measuring the incoming light:

  1. Matrix or Evaluative Metering – the camera looks at the light in the entire scene and averages it, (Nikon puts a bigger emphasis on the area where your lens is focused as well). Nikon calls this Matrix Metering, Canon calls it Evaluative.
  2. Center-Weighted Average Metering – looks at the light of the entire scene and averages it, but with emphasis on the center of the frame. Nikon and Canon both call this Center-Weighted Average Metering.
  3. Partial Metering – this measures the light only in a small portion of the center of the frame (about 8-12% of the scene). This is a Canon metering mode, Nikon does not have one similar.
  4. Spot Metering – measures the light only in a small area around the central autofocus point (about 1.5-3% of the frame). Nikon and Canon both call this Spot Metering.

Other camera manufacturers have different names for these modes, but suffice it to say the way in which your camera measures incoming light can have a huge impact on whether your photo is properly exposed. As an example, here are three shots that were taken with different metering modes.