Capturing the Moment: Shutter Speed and Focus
Your camera’s shutter controls time, opening and closing to allow the right amount of light to reach the sensor and record the scene. The duration of that interval affects image sharpness and exposure, and can be used as a creative tool. The shutter speed controls the amount of blur (or lack thereof) of moving objects in the picture. Andrea Blum’s picture froze the skater and his board in mid-air in 1/1250th of a second. Peggy Kelsey wasn’t worried about fast action, but did need to time her shutter-press to record the interaction between the girls in this picture at just the right moment. She also had to work with a lot less light than that of a bright sun. Slower shutter speeds let us close the lens aperture down to improve depth of field, or we can open it to isolate the area in sharp focus. The exact speed needed varies with distance and the direction the subject is moving, relative to the camera.
Freeze Frame: How Fast Is Fast Enough?
Gary Todoroff’s picture makes use of shutter speed to blur the bird’s wing tips to show their motion. The visual message would have been different if he had used a faster speed to freeze all movement. The “correct” shutter speed depends on what effect the photographer wants to produce. Obtaining that effect requires understanding, and applying, the basic principles of controlling motion with the shutter and your camera technique. Suppose you are on a train and want to take a picture of someone in a window on another train traveling right next to you. If the trains are both traveling in the same direction, at exactly the same speed, the shutter speed is of little concern. If one is slowly overtaking the other, then a fast speed is needed. If they are coming toward each other at high speed, you may not even be able to react in time to take the picture. Let’s look at three examples of the same activity taken at three different angles.
The horse and rider were perpendicular to the camera. Bob Cieszenski was using a 200mm lens (300mm full-frame) and a 1/1000th of a second shutter speed. Had he been closer, or using a longer lens, the speed would have had to have been faster to get the same effect. Consider the timing involved: The horse is moving forward and up; the picture shows the animal completely off the ground and just broaching the obstacle. It takes practice to capture just the right 1/1000th of a second.
The minimum shutter speed needed to totally freeze motion varies according to: the speed the subject is traveling, the direction of motion relative to the camera, the distance between the two, and the focal length of the lens used. A subject moving perpendicular to the camera requires twice the shutter speed of one moving at a 45-degree angle, and four times that of one moving directly toward it, if all other factors are equal (velocity, distance, lens). So if the perpendicular speed needed is 1/1000th of a second, the 45-degree is 1/500th, and the head-on is only 1/250th. If there is enough light, most sports photographers use a speed that will stop motion for any angle with the lens in use at a reasonable working distance. The image below shows another horse and rider, this time at a 45-degree angle. The exposure time is 1/750th of a second and the focal length on the zoom was set to 170mm. That’s the same as a 225mm on a full-frame sensor. Since we don’t know the exact distance between the camera and subject in the two pictures, it’s impossible to compare the relative effect of the shutter speed.
Let’s look at some comparisons. At 75 feet with a 300mm lens on a full-frame sensor, subjects moving at five to ten miles per hour will appear motionless with a shutter speed of 1/250th of a second, as they are moving toward or away from the camera. You’ll need 1/500th of a second for subjects moving at a 45-degree angle, and 1/1000th of a second for perpendicular movement. Move back to 300 feet with the same equipment, and the speeds drop to 1/250th, 1/125th, and a mere 1/60th respectively. The next picture shows another horse, this time jumping directly at the camera. Horse and rider are both sharply in focus and movement is arrested.
The exposure was 1/1000th of a second at f/3.2 with the zoom set to 160mm, the same as a 240mm lens on a full-frame sensor. There are tables available that provide suggested shutter speeds for various conditions, but a few basic rules of thumb will handle most situations. Human-powered team sports will all freeze with up to a 300mm telephoto (full-frame) at a 1/1500th of a second. Raise the shutter speed to 1/2500th of a second, and bike races and running horses will stop at the press of a button. Flying birds, baseball swings, and race cars need at least a 1/4000th of a second. If you have a long telephotosay, over 500mmthen double the numbers.