Exposure

Now that you know about shutter speed and aperture we need to learn how they work together.

A photograph is properly exposed by having the right amount of light hit your image sensor. If too much light hits your sensor your picture will look too bright and be overexposed. If you don't get enough light your picture will look dark and underexposed. Proper exposure is critical to the quality of your image.

In years past it was necessary to purchase extra equipment to measure the light falling on whatever you wanted to photograph. Lucky for you, all DSLR's come fully equipped with an exposure meter. If you learn to use it right you will get a properly exposed picture every time.7

Your camera will tell you the settings you need for aperture and shutter speed. If you take that setting and speed up the shutter speed you will get an underexposed photograph since less light is getting in. If you have a slower shutter speed you will get an overexposed picture. If you close down the aperture (higher f-stop number like 22) your aperture will be smaller, letting in less light and you'll get an underexposed picture. If you open up the aperture (lower f-stop number like 4.0) you will let in more light with a larger opening, and you will get an overexposed picture.

Using Exposure Modes

As I mentioned earlier most amateurs us the P mode. This lets the camera choose the aperture and shutter speed. That makes it easy, but it also gives you the least interesting photos. You might as well be using a cheap point & shoot camera.

Somewhat more advanced and useful are the Av (A) and Tv (S) modes. In Av (A) mode, you are telling the camera what aperture you are going to use. Let's say it's 2.8. Your camera's light meter will determine what shutter speed it needs to properly expose. As the amount of available light on your subject changes so will the shutter speed to compensate. But your aperture will stay wherever you set it. The same can be said about Tv (S). The difference is you set the shutter speed while the camera automatically adjusts the aperture setting.

There are some professionals that will use Av (A) and Tv (S) modes. There is a simple reason why I don't use these modes. Consistency. Your camera will check and change the exposure for each picture you take. Sometimes if your sensor is reading a slightly brighter or darker object in the frame, and your exposure can change from image to image. I prefer to set it once for a set of pictures of the same scene. This way the exposure is the same for all of them. If consistency within a set of pictures isn't critical for you or you are constantly changing scenes then Av/Tv (A/S) modes may work fine for you.

Proper Exposure In Manual Mode

Now it's time to start thinking like a pro! The first thing to do is turn that dial to M, and leave it there.
The first step in setting the right exposure is deciding if aperture or shutter speed is most important to you for this shot. When you decide what either of those should be you will set that. Then look in your viewfinder to finish your exposure.8

There should be a circle or box in the middle of your frame when you look into your viewfinder. This is the area the camera uses to determine your exposure. What you do is point that circle at the subject you want your camera to expose on. I'm a portrait photographer, so I like to expose off of the person's skin. I will put the circle on my subject's face and press the shutter button half way down. This will give me an exposure reading below the picture I'm looking at.

Let's say I set my aperture at 4.0. Your shutter speed is probably too fast or two slow. There's a chart below your image in the viewfinder that will point to where your exposure is with your current settings. My camera goes from 2 stops underexposed to 2 stops overexposed. The zero in the middle indicates a perfect exposure.

What you do at this point is keep your camera pointed at your subject so that what you want to expose on has the center over it. My aperture is already set so now I want to adjust my shutter speed until the indicator on the exposure graph below the picture is under the 0 mark. Now your exposure is set, and it won't change until you change it.

Not all cameras have their exposure meter calibrated perfectly. You may notice a trend in your camera's metering. For example, you may find that your camera overexposes by about a half stop. If that's the case you can simply target -0.5 on the chart to compensate. But this will take some trial and error as well as time to figure out for your specific camera.

Some cameras have features that will allow you to set this compensation into your settings, but that is beyond the scope of this book. Read your owner's manual to discover your options.