Exposure - Photography

The actual shot is simply exposure. Now think about that, you can only see items because there is a reflection. So exposure is how much light is coming back and exposing the camera. Back in the day, it was the film being exposed, now it's sensors.

There are two things you want to use to control exposure however there is a third (if needed). These three settings join together to create what is commonly referred to as the Exposure Triangle.

1. Aperture
2. Shutter speed
3. ISO / Film speed

Depending on your situation, you will want to prioritize them accordingly. For example, you don't want to have a low shutter speed for a situation where there is a lot of movement. You wouldn't want to have a high ISO in a well lit environment. You probably don't want to have a large aperture for a shot where you want the overall picture to be focused.

The first thing is to understand how you can understand exposure.

Understanding your exposure meter

Most cameras have an exposure meter. This confused me early on because I thought it was the bar that controls exposure. It was my first time shooting and it took a while for the word "meter" to sink in. The exposure meter simply shows you what the above three settings will result in as far as exposure is concerned with your exposure metering. Exposure metering is also something to be covered but that will be done later.
For most use cases, you want to have the exposure meter bar centered.
Example of an exposure meter:

- |..|..0..|..| +
        *

Example of an exposure meter reading zero:

Understand that your camera may place negative / positive at different places. Notice the bars and dots. Each dot is 1/3 EV (i.e. Exposure Value). Your camera may use dashes or dots or whatever. But you will most likely have a way to know when you move somewhere by a third and when you move by a full integer EV (e.g. -1 EV). In the above example, I am using a dot for a third and a bar / pipe for a full integer EV. I am using an asterisk to basically state that the exposure meter is reading that the view is perfectly exposed (i.e. it's reading 0 which is neither over nor underexposed).

Here is an example of under-exposing by 2/3rd's of an EV.

- |..|..0..|..| +
      *

Here is an example of over-exposing by 1 EV.

- |..|..0..|..| +
           *

Your camera probably won't use an asterisk to let you know but play around with it and you'll figure it out. If not, hunt down your camera manual.

What your exposure meter is metering

Most of the time your exposure meter will correctly calculate the exposure values. However in certain instances it may not work well.

Cameras often have three metering modes:

1. Matrix / Full
2. Center-weighted
3. Spot

Matrix

Matrix metering takes the entire area into consideration. The top right, center, bottom left, etc etc. Sometimes this works, but other times it may have a negative affect. Imagine you are taking a picture where you want to photograph the sun in the top right and a person in the center with the sun behind them. If you follow matrix metering, you may end up with a picture that under exposes the person in the center. You can just fiddle around with the Exposure Triangle but you may risk losing detail. This is when you want to see if the other two metering modes will be of service.

Center

Center-weighted metering will take the lighting conditions of the center area into consideration and nothing else. This mode is often used for portraits. This mode will help with the above picture since the exposure meter will show you that the center is under-exposed. From there you will adjust the Exposure Triangle accordingly and hopefully not lose much detail.

Spot

Spot metering will take the area that you have chosen as the focus area. In many cameras you can choose to tell the camera to focus at a certain point or area. Basically exposure metering will also be decided by that area. So let's imagine that we have a picture of the sun in the top right, a dog in the center (in the shade) and a dog house on the left (in the shade). You want to take a nice picture of the dog house but you want the dog to be in the center of the picture. You will want to tell the camera to focus on the left (dog house). Once you choose the focus area, the camera will determine the current exposure values and show them on the meter. You will now have a better idea of how to adjust the Exposure Triangle to get the most bang for your buck.

Addendum

A message to those interested. Most of the time matrix metering will work. You can still make it work even when it doesn't by adjusting the Exposure Triangle. You want to use the other modes when you know what you are looking to do and or want as much detail as possible on the item you are interested in. The reason is because matrix is considering everything and it's not considering what you want. Some may feel the other metering modes should never be used, however that is not the case. You can get the job done faster by adjusting your metering mode and hold onto more detail.