A waterfall that looks like soft mist, or an athlete whose movement shows in every drop: Both pictures are created by the same setting on your camera. The exposure time determines how long light hits the sensor, and thus also how movement looks in the image. In this guide, you will learn how exposure time works, why the values seem so odd, and how to use them for sharp, blurred, or natural-looking shots.
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Key Takeaways
Key Takeaways
- The exposure time indicates how long the image sensor takes in light. Typical values are fractions of a second, for example 1/50 s or 1/8000 s.
- The shorter the exposure time, the less light gets into the camera. With longer times, you correspondingly need less light.
- Movements are frozen by short times and blurred by long times. This creates motion blur, which can come from you as well as from the subject.
- As a rule of thumb for shake-free handheld shots: The exposure time should not be longer than the reciprocal of the focal length (20 mm means 1/20 s).
- The values 1/50 s to 1/100 s look natural because they show movement the way your eye perceives it.
Step-by-Step Guide
Step 1: What exposure time actually measures
The exposure time describes how long the camera exposes an image. It is measured in fractions of a second, and for long exposures also in whole seconds. An eighth of a second sounds like a tiny moment in everyday life, but for a camera it is an enormously long time. On modern models, the scale goes up to 1/8000 s. That is such a brief instant that the actual exposure takes place within it. Remember this relationship: The value on the display is always a duration, not a brightness.
Step 2: The shutter inside the camera
In a DSLR camera, the mirror first flips up so that the image sensor is uncovered. Then the focal-plane shutter travels from top to bottom. The first curtain uncovers the sensor, and the second follows right behind it. The time between the two curtains is your exposure time.
If the exposure time is very short, it is not enough for the first curtain to run through completely before the second one follows. The camera then photographs in strips that are exposed one after another. This behavior is technically determined and a compromise you accept with very short times. You will learn more about this in a later lesson on light and flash.
Step 3: Understanding fractions and stops
At first glance, the steps of the exposure time seem illogical. You jump from 1/50 s to 1/100 s, for example, even though the numbers do not follow the same spacing. The reason lies in the stop, a unit of measurement for exposure. One stop means that the amount of light is halved or doubled. So if you switch from 1/50 s to 1/100 s, only half as much light falls on the sensor.
Some cameras also display the values in third steps. For getting started, it is enough to know that each step is a halving or doubling of the amount of light.
Step 4: Recognizing motion blur
The longer you expose, the more time every movement has to be recorded in the image. This is called motion blur. It can come from two sources.
The first source is your own hand. If you hold the camera unsteadily during a long exposure, the entire image becomes blurred from shaking. The second source is the subject itself. A fast jogger or a passing car becomes blurry with a longer exposure, even if you put the camera on a tripod. So you cannot avoid every blur simply with a stable tripod. You also have to keep an eye on the subject.
Step 5: Using frozen or blurred motion deliberately
With short exposure times, you freeze movement. This is very effective for sports, high-speed photography, or fast-flowing water. A jump or a water droplet stands still, and you can recognize every detail.
With long exposure times, you create the opposite effect. Moving objects turn into lines or veils. A classic example is waterfalls, whose water looks soft and silky. Car headlights in the dark also create long light trails, because the vehicles cover a large distance during the exposure. Such shots often require a neutral density filter in front of the lens or little ambient light. A detailed lesson on long exposure follows later.
Step 6: The Reciprocal Rule for Sharp Handheld Shots
If you shoot handheld and want to capture a stationary subject sharply, a simple rule helps you. The exposure time should not be longer than the reciprocal of the focal length.
The focal length is printed on the front of your lens, for example 20 or 40 for 20 mm or 40 mm respectively. At 20 mm, you therefore need at least 1/20 s to get images free of camera shake. At 40 mm, the limit is 1/40 s. With an image stabilizer, you can often get by with longer times as well. Nevertheless, the rule is a reliable guideline that you can depend on.
As soon as you want to expose for longer, it is best to use a tripod and set the camera up firmly. Then nothing will blur from shaking anymore.
Step 7: The Natural Value 1/50 s
Movement should not always look extremely frozen or extremely blurred. Often you want a depiction that comes close to human vision. The value 1/50 s is suitable for this. It comes from the film industry, where it softens the transitions between individual frames. Without motion blur, a film would look like a flip book.
A good example is a fountain. With a long exposure, the water looks like mist, and with a very short time, every drop is frozen. At 1/50 s, you see the movement of the water without it becoming blurred. This corresponds quite exactly to the impression you have with your own eyes when you stand in front of the fountain.
Step 8: Experimenting with Shutter Priority
The best way to develop a feel for exposure time is to try things out. To do this, set the shutter priority mode on the mode dial. On Canon it is called Tv, on Nikon S, and on Sony and most other manufacturers S (Shutter). In shutter priority mode, you choose the exposure time yourself, while the camera calculates the aperture and ISO to match.
Turn the appropriate dial until the desired time appears in the display, and photograph moving subjects with short and long values. An image that is too bright or too dark is not a problem here, because the main point is to get a feeling for when a subject looks frozen or blurred.
Step 9: Recognizing the Limits of Your Camera
The camera can only work within its technical range. A 30-second long exposure in the midday sun is not possible, as the image would be overexposed immediately. Conversely, an exposure time of 1/8000 s cannot be achieved at night without light. Most cameras display a warning on the screen when you reach these limits.
When that happens, it is worth taking a look at the other settings. A wider aperture or a higher ISO sensitivity can help to achieve the right exposure. The next lessons cover the relationships between these values in detail.
Summary – Understanding Exposure Time: Deliberately Controlling Motion in Photos
The exposure time determines how long light falls on the sensor, and thus how motion appears in your image. Short times freeze movement, while long times blur it into soft trails. For handheld shots free of camera shake, you orient yourself by the reciprocal rule. The value 1/50 s delivers a natural-looking depiction of motion. With shutter priority mode, you can try all of this out in practice and get to know the limits of your camera.
FAQ
What exactly does the exposure time indicate?The exposure time indicates how long the image sensor collects light during a shot. It is usually given in fractions of a second.
Why do the exposure time values seem so illogical?The steps are based on aperture stops. Each step halves or doubles the amount of light, which is why the numbers do not follow an equal mathematical spacing.
How can I freeze motion in the image?Use a short exposure time. The faster the subject, the shorter the time should be.
What is the reciprocal rule?For handheld shots, the exposure time should not be longer than the reciprocal of the focal length. At 50 mm, that would be at least 1/50 s.
How can I recognize motion blur?Motion blur appears as smearing of moving areas. It is caused by movement of the camera or by movement of the subject during the exposure.
Why is 1/50 s so popular?This value creates a natural motion blur that resembles human vision. It is also frequently used in the film industry.
What does shutter priority mode mean?In shutter priority mode, you set the exposure time yourself, and the camera automatically calculates the aperture and ISO.
