Understanding Your Camera's Light Meter

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Let's take it back to the basics and remember our three keys to making a good exposure: aperture, shutter speed and ISO. It is pretty complicated to look at a scene with just our eyes and determine what our exposure should be; what these settings need to be to make an image that is balanced as far as lighting is concerned. Luckily, we don't have to guess how to make a great exposure; we have an amazing tool built into our cameras to help us figure it all out - the light meter!

Cameras have built-in metering points that read the intensity of light throughout your scene. Light is recorded through your lens (TTL) to your sensor and your camera translates what your exposure will look like on your light meter. When you shoot on Auto, pressing the shutter release button half way determines the best exposure reading for that scene. You can choose your exposure by shooting in one of the creative modes (such as Manual, Aperture Priority or Shutter Priority). This is where using your exposure meter is crucial - it will tell you when you are in the ballpark of having a well-exposed image.

Your built-in light meter looks something like this:  

You can see this when looking through your viewfinder, and on some cameras you can also see it on your LCD screen. When the tick mark (see red arrow) is lined up in the middle, your camera is telling you it is a good exposure. If these tick marks line up towards the positive numbers, your image will be too bright (overexposed). If they line up below the negative numbers, your image will be too dark (underexposed).

In these images below, you will see the light meter through my viewfinder. This image would be too bright. My ISO number is pretty high, letting in a lot of light. Think (+) as too much light.

This image below would be too dark. I dropped my ISO to 125, which will make my image very dark. Think (-) as not enough light.

When my tick marks line up with 0, I'll have a good exposure. I changed my shutter speed and my ISO to get the right combination. 

Remember that your camera is giving you it's best opinion; it won't always be perfect. Sometimes your image will be a little too dark or too bright even if your meter is lined up at 0 (like my example in my previous post, tips for shooting in the snow). Use your meter as a reference point and then determine whether you need to make it brighter or darker. I tend to overexpose one or two stops in a lot of scenarios. 

Switch your camera to Manual Mode to practice and watch the arrow on your exposure meter change. Try to get a combination of your aperture, shutter speed and ISO that will place your arrow closest to the middle of your exposure meter. If you want a blurry background, keep your f/stop number low and change your ISO and shutter speed until you get a good exposure. If you need a fast shutter speed to freeze motion but your image is dark, try a lower f/stop number or a higher ISO to let in more light. See how the settings work together to give you the best exposure! Practice, practice, practice! 

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Learning About Exposure

Exposure is the amount of light that creates your image. The main goal of each image you take is to use three key elements correctly to make a good exposure. The three elements are your aperture (f/stop), shutter speed and your ISO. 

• Aperture (f/stop) - This is the setting that tells you how much light will enter into your camera. This also changes your depth of field.

• Shutter Speed - This number indicates how quick or slow your shutter opens and closes to let in light. The faster the shutter speed, the sharper your image will be. A slow shutter speed can cause motion to blur, or show camera shake.

• ISO - is how sensitive your sensor is to light. The lower the ISO number, the sharper your image will look, but you will need a decent amount of light for a good exposure. The higher the ISO number, the more grain/noise you will notice (not as sharp) BUT this will allow you to take images in a darker setting.

The image on the left is definitely dark; this is called under-exposed. My shutter speed was too fast, and didn't let in enough light. The image on the right is over-exposed. This is when an image is too bright or 'washed out'. The white areas on the cake and the platter start losing detail from the image being too bright. On this image, I had my ISO a little too high and it let it more light than I needed. The middle image is an example of a good exposure!

On your camera's display screen and when looking through your viewfinder, you will see your exposure meter (see image below). Your camera will tell you when your settings will get a good exposure when the notches below the meter line up at the 0. When they fall to the left, or towards the (-) mark, that means your photo will be underexposed (too dark) and when they fall towards the (+) mark, your photo will be overexposed (too bright). Depending on your lighting situation, you might want your image a little brighter or darker than what your camera tells you. Use your exposure meter to help guide you as you change your settings!