Aperture refers to focal length, or the size of the lens opening when you take the photo. The larger that opening, the more light the camera takes in during the shot. This is measured in f-stop values, written as f numbers in a slash notation. Common f-stops include f/2.8, f/4, f/5.6, f/8, f/11 and f/16. The larger the number in the f-stop, the smaller the aperture. Thus, f/22 is a much smaller opening in the lens than f/4.
When it comes to photography, aperture and shutter speed are inseparable. As you increase the aperture, you'll need a faster shutter speed to avoid getting too much light in the shot. Likewise, smaller apertures require slower shutter speeds to ensure the photo has enough light. Freezing a shot in high-speed photography often means sacrificing aperture for the sake of a higher shutter speed.
Fortunately, your camera probably has automatic modes that balance shutter and aperture settings for you. Many cameras have the option to select between two of these modes: shutter priority and aperture priority. In high-speed photography, you'll want to select shutter priority. Then, you can adjust your shutter speed to fit your subject, and the aperture will adjust automatically based on how much light's available for the shot.
When sacrificing aperture for your high-speed shots, you should also note the change in your depth of field (DOF). The DOF refers to the amount of the shot that will be in focus. If your aperture is larger, your DOF will be smaller, meaning less of the photo will be in focus. Note this when framing your high-speed shots: You should select a focal point for the shot that ensures your subject will be in focus, even if other portions of the shot are not in focus.
Even if you have the perfect combination of camera settings, you still have to press the button and take the shot. Are you fast enough to capture your subject? Our next tip can help reduce the delay between action and snapshot.