The Exposure Time

One of the three pillars of photography is exposure time. The other two are aperture and ISO. Exposure time is responsible for two things: changing the brightness of your photo and creating dramatic effects by freezing or blurring. In this chapter of the basics of digital photography, I will simply explain everything you need to know about exposure time.

How does your digital camera expose?

The exposure time exists thanks to the so-called shutter. Put simply, it’s a kind of curtain that stays closed and covers the camera sensor until you pull the trigger. When you press the shutter release button, the shutter opens and light can fall through the lens directly onto the sensor. As soon as the sensor has absorbed enough light, the shutter closes and locks out the light again. The release button is also called the shutter or interlock button because it releases the shutter.

Do you want to know what that looks like?

What is the exposure time?

Exposure time is the period of time when your camera shutter is open and projects light onto the camera sensor. Essentially, it’s about how much time the camera spends taking a picture. This in turn affects how your photo will look.

If you select a long exposure time, you expose the sensor for a longer period. This creates an effect called motion blur. This makes moving subjects in your photo appear blurred along the direction of movement. This effect is often used in car and motorcycle advertising to give the viewer a sense of speed and motion by intentionally blurring the moving wheels.

Long exposures are also used to photograph the Milky Way or other objects at night or in dark environments with a tripod. Landscape photographers often deliberately choose long exposures to create a sense of movement in rivers and waterfalls while everything else is in focus.

On the other hand, you can also use the exposure time for the opposite – namely for freezing movements. With an especially short exposure time, you can easily stop movements of fast-moving objects, such as flying birds or moving cars. If you photograph water in this way, every drop remains completely sharp in the air. To the human eye, such a thing is normally not visible.

You can easily control all this with this one setting. To recap: Short exposure times freeze objects, while long exposure times create motion effects.

How to measure the exposure time?

Typically, the exposure time is measured in frames per second, if it is less than one second. For example, 1/4 means a quarter of a second, while 1/250 means two hundred and fiftieth of a second (or four milliseconds).

Most modern SLR cameras and mirrorless cameras can achieve exposure times of up to a 1/4000 second, while others can process much faster times of up to 1/8000 second and faster. On the other hand, the longest possible exposure time of most DSLRs or mirrorless cameras is typically 30 seconds. With such long exposure times, you may need a remote shutter release.

Further influence of the exposure time

The exposure time also affects the brightness of your image. With a long exposure time, the sensor absorbs a lot of light and the photo becomes correspondingly brighter. If the exposure time is short, the result will be a darker photo because less light can get in.

However, the exposure time is not the only thing that affects the brightness of an image. Aperture and ISO are equally important – along with the actual brightness of the scene, of course. This results in a certain flexibility when you decide on exposure time. The other settings have to be chosen carefully as well because all three sizes influence the image and are related. You can see these connections here on the so-called exposure triangle.

The exposure time can be an important tool to take a photo with the right brightness. On a sunny day, you probably need to keep them short so that your photo is not overexposed. In darkness (e.g. in night photography) a long exposure time is necessary for you to see anything at all in your pictures. You may also need a tripod for this because camera movements can lead to blur at long exposure times. After all, the brightness of the image is the reason why most people deal with exposure times at all. Motion blur is also an important point that should not be ignored.

Short exposure times: Stop the time

You need a short exposure time to freeze a movement. When you photograph flying birds, it can be 1/1000th of a second or faster. With slower subjects, 1/200, 1/100 or less is probably enough to produce an image without motion blur. If you want to freeze something for testing, the following motives are suitable:

• Animals (running dogs, horses etc.)
• Driving cars without light trails
• Sports Events
• Skydives
• Etc.

Long exposure times: Bring movement into the picture

You talk about a “long” shot at over 1 second – from then on you need a tripod to get still sharp pictures. This can be used in low light conditions, at night or when you want to blur something intentionally. If something moves in your photo now, it will appear blurred. You can use long exposure times well for the following photo ideas, for which in most cases you can find instructions in this section:

• Waterfalls with haze effect
• Beaches / Sea / Sunsets
• Light tracks from moving cars
• Night sky and astrophotography / Moon
• Lightpainting with steel wool
• To remove moving subjects from an image

Movement is not a bad thing per se. You want to show how a waterfall flows, how waves move, how fast a racing car drives or how stars in the firmament move with time. Movement can be a great stylistic tool. In these cases, the choice of longer exposure time is the right way. However, a tripod is essential here, otherwise, there is a risk of camera shake (not to be mistaken with motion blur).

Additional good application possibilities for this technology are:

• light painting
• Showing partial movements (e.g. hammering construction workers)
• Fireworks
• If there is not enough ambient light

Practical tips and summary

• The exposure time is measured in frames per second. The higher the number, the shorter the exposure time (1/1000 is much shorter than 1/30).
• You will usually need 1/60 or more. Any longer exposure times will probably cause camera shake.
• For long exposures (1/60 or lower) you need a tripod or an image stabilizer.
• The times available on the camera double / halve (approximately) with each adjustment. This results in the following options: 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, etc. You should better remember this doubling because the aperture values are very similar. They also double/halve the amount of incident light during an adjustment. According to this, an increase of the exposure time value by one “click” and the simultaneous decrease of the aperture value by one click should lead to a similar exposure again.
• Some cameras give you very long exposure times, which are then measured in whole seconds instead of fractions of a second. This is helpful in low light conditions or if you want to do something with special effects. You may even have the letter “B” (Bulb) on your mode wheel. In this mode, the shutter remains open as long as you hold down the shutter-release button. By the way, this is how long exposures are made.
• Before you set the exposure time, you should always consider whether something in your image is moving and how you want to capture that movement. Freeze or blur, that is the question here.

The exposure time is an element that, if used correctly, offers you numerous creative possibilities. One thing is for sure: This is basic knowledge and if you want to photograph seriously, you simply can master it now. So grab your camera and go practice!