The world is dynamic, full of motion, and rarely slows down for a picture. Depending on your subject matter and your artistic intent, you can either freeze the action you see or allow its movement to show through the photograph as motion blur. However, to do this effectively, you must select the right shutter speed for the situation.
Shutter speed, subject motion, and your frame
The standard recommendation for managing the appearance of movement using the shutter is to consider the subject distance, direction of travel, and your focal length. Although this advice is technically correct, it’s far more helpful to understand the fundamental principle upon which it’s based. Additionally, understanding this principle allows you to handle challenging conditions beyond the basic lateral movements with which the standard recommendations aim to assist you, such as receding, approaching, and rotational motion.
To fully understand how shutter speed affects the perception of motion in a photograph, it’s important to consider your subject’s movement in relation to your frame and not in terms of absolute velocity. For example, the cruising speed of a typical passenger jet ranges from 860–930 km/h. When viewed through a super wide-angle lens, it can take one or two minutes to traverse the frame, but when seen through a super telephoto lens, it can take several seconds, even though the plane’s velocity is constant. Changing the angle of view alters the magnification of the aircraft. How does this affect shutter speed and motion?
The speed of your subject within the frame is the cardinal principle for determining the appropriate shutter speed necessary to freeze movement or show motion blur. Imagine an object (with an unknown distance and velocity) that takes precisely one second to move across your frame. In one-half a second, it travels across half of the frame. In 1/50 second, it moves across two percent of the frame. Now, assume your shutter speed is 1/100 second, and your camera’s image sensor is 6000 pixels wide. At that shutter speed, light from the moving object would pass across 60 additional pixels during the period of exposure, resulting in 60 pixels of motion blur.
The “right” shutter speed
This guide intends to empower you with a solid foundation of photographic knowledge and concepts that you can turn into heuristic experiences of trial, error, and discovery. Accordingly, there’s no single universal prescription or rule-of-thumb for determining the right shutter speed for every conceivable situation. Not only are there too many variables, but the most critical variable—your creative intent—is highly subjective. An effective way to become intuitively familiar with the effects that different shutters speeds have on various types of motion is to experiment. Set your camera into shutter priority mode, select a shutter speed that you think is suitable for your subject matter, and snap away. Check your results periodically and pay attention to the exposure settings of the pictures you appreciate. If the results aren’t satisfactory, change the shutter speed in the appropriate direction for the desired effect: increasing shutter speed until it freezes motion or decreasing shutter speed to increase motion blur.