You have your subject, you have your camera, and you want to take complete control over your photograph. To get the best in-camera shot possible you need to understand exposure.
Simply put, exposure is light striking a sensor (or if you’re going old-school, a frame of film). You control exposure with three parameters, Aperture, Shutter Speed, and ISO. This is what’s called the Exposure Triangle:
Let’s get into some detail of each:
Shutter speed is the measure of time that a sensor or frame of film is exposed to light. By controlling how long you blast light into your camera, you decide how time is stopped in that final image. The difference between a hundredth of a second and a thousandth of a second can be the difference between getting an epic shot and not getting a usable image at all.
1/2000 sec; f/2.8; ISO 800 Canon 7D; EF300mm f/2.8L IS USM
Your choice of shutter speed comes down to what you want in your picture. Do you want your subject to be frozen so that you can clearly see all detail? Or do you want something more abstract, where blurred lines show movement? Remember, fast shutter speeds mean less time for light to hit the sensor, so the faster the shutter speed the less light available for the image. If fast is necessary, then aperture and ISO are on your side to help obtain the image you desire.
The opening of the lens, otherwise known as the aperture, is both a technical and artistic tool for you as the photographer. By deciding 1) what lens to shoot with 2) what focal stop (f-stop) you prefer and 3) how far you want to be from your subject, you’ll be controlling the exposure and depth of field of the photograph.
When you change the size of the aperture opening you change the amount of light and also alter the path that the light travels. This changes how much of the scene will be rendered sharp and in-focus. The in-focus area is defined as the depth of field. A shallow depth of field isolates a focused area from the rest of the background, a large depth of field will show most of the scene in focus. Depending on how you want your image to look while still allowing what you deem is the right amount of light to hit the sensor is where you’ll find aperture playing a role in your artistic vision.
Min depth of field vs Max depth of field
If you’re using film, your choice on ISO is limited to what the box of film says, but when you shoot digitally the ISO becomes a tool to work within exposure. ISO describes the sensitivity rating of your camera’s sensor. The sensor records the light that enters through the lens, passing through the aperture opening and moves past the shutter unit. The ISO settings can be adjusted to change the sensitivity. With higher ISOs come an increase in noise, or if using film, grain. When you use a higher ISO (say around 1600 or 3200) the camera will capture a photo with less light coming into the camera. The lower light level is then amplified so that the final image is of normal brightness. You can use a faster shutter speed with a higher ISO in a low light scenario, at the cost of a lower image quality (due to the noise).
By understanding the exposure triangle and how shutter speed, aperture, and ISO work together, you can go out into the field in a variety of lighting scenarios and know how to adjust the parameters to meet the needs of the image you want to capture.
Want to know more about exposure? You’re in luck. I wrote the book on it. The Enthusiast’s Guide to Exposure is now available everywhere books are sold. In it, you’ll find 49 photographic principles that will teach you how to shoot great images in a variety of lighting situations and gain the knowledge you need to shoot the photos you want.