Camera exposure is one of the most important terms that confuse many photographers, especially beginners. Photography is all about light, and when you find your perfect shot or scene composition, the next step is to tell your camera how to interact with the light that goes through its lens to form the final image. If your camera is a light receiver, there are many factors that affect the light when it goes through the lens. These factors can be:
- The duration of receiving the light.
- The width of the area that receives light.
- The camera’s sensitivity to light.
In the photography world, the above-mentioned factors are referred to by three main terms: shutter speed, aperture, and ISO. Before we learn how these three terms affect the total exposure of your shot, let us understand what each term means:
- Shutter Speed refers to the speed your camera shutter opens and closes when you press the camera button.
- Aperture refers to the amount of light that passes through the lens to the camera sensor.
- ISO refers to the camera sensor’s sensitivity to light.
We will talk about each term in more detail and its relation wit camera exposure later in this article.
Camera Exposure Factors
The famous camera exposure triangle below shows how the shutter speed, aperture, and ISO are combined to form the total definition of camera exposure. The balance between the values of these three items will help you to get professional photographs. In some cases, you may need to play with different combinations of these values to get more sophisticated and artistic effects in your shot.
Understanding Camera Shutter Speed
As we have mentioned earlier, the shutter speed refers to the duration that your camera shutter stays open and receives the light. This duration determines how much light gets through the camera lens. A long shutter opening time (slow shutter speed) means the following:
- More light and brighter shot.
- More blurred and soft-edged shot.
When you are shooting with a slow shutter speed setting, you will need to use a tripod in order to get a steady shot, as the shutter stays open for a quite long time.
You can use a slow shutter speed to take soft and a little blurred shots, such as sea waves and waterfalls (see the figure below).
On the other hand, a short shutter opening time (fast shutter speed) means the following:
- Less light and darker shot.
- Sharp shots with clear details.
A fast shutter speed is usually used to freeze the motion and allow the camera to get the light of a specific fast shot, such as sports events and pictures of fast moving objects (see the figure below).
In general, the shutter speed has some ranges that you can keep in mind when you are setting up your digital camera exposure:
- The range between 1/2 and 1/50 is suitable for creating a blurry effect and is more suitable for landscape photography.
- A shutter speed ranging from 1/50 to 1/100 is a good choice for daily photo shots.
- The values between 1/200 and 1/500 are suitable for sports and moving subjects.
- 1/1000 and above is useful to freeze very fast movement.
Understanding Camera Aperture
Unlike shutter speed, understanding the aperture is little bit tricky. Each camera lens has blades that control the amount of light passing through the lens to the camera sensor.
The camera aperture, or f-stop, controls the light getting through the lens, and the depth of field or a blurry background vs. foreground.
Let us start with the light first, as the aperture f-stop value has a double impact on the light. For example, when you increase the f-stop by one, the amount of light received decreases double that amount.
The figure below can clarify this point:
You may notice that along with each increase in the f-stop value, the lens diameter is reduced to limit the amount of light passing through the lens.
The math behind this value is very simple and is based on one simple equation:
N refers to the aperture number, f is the lens focal length, and D is the lens’s pupil diameter.
The aperture also affects the depth of field, which is the distance where the objects still appear sharp. For example, a low f-stop number produces a blurry background and clear foreground (shallow depth of field). This is called wide aperture (see the figure below).
On the other hand, a high f-stop produces clear foreground and background, which means large depth of field (narrow aperture). See the figure below.
Understanding Film ISO
The ISO concept is actually based on old film cameras and the film’s sensitivity to light. In the digital world, the ISO refers to the camera sensor’s sensitivity to light. A low ISO means that the sensor is less sensitive to light. You can use a less sensitive ISO value for sunny or highlighted scenes to allow the camera to sense a lower amount of light.
A high ISO means that the camera is very sensitive to light which can be used for dark scenes when there is not enough light and you want the camera to be sensitive to any amount of light. But you have to remember that a high ISO can produce image noise, which are small dots that appear in the shot, also known as film grains in film photography.
Digital Camera Exposure Modes
Each digital camera has a shooting mode wheel that allows you to choose between different exposure setting standards. With regard to camera exposure, there are a number of modes, such as:
- Auto mode, when the camera automatically sets all the settings.
- Manual (M), you set up the shutter speed, aperture, and ISO values.
- Program (P), the camera sets the aperture and shutter speed and lets you set up the ISO.
- Aperture Priority (Av or A), the camera sets the shutter speed and lets you set up the aperture and ISO.
- Shutter Priority (Tv or S), the camera sets the aperture and lets you set up the shutter speed and ISO.
- Bulb (B), you can use this setting for long exposures, as you can see the ISO and aperture and set the shutter speed manually through a remote release.
Using any of the above settings depends on the shot you would like to take and which settings you use the most.
In this article we got through one of the most important concepts in photography, which is camera exposure. Setting up your camera based on the shutter speed, aperture, and ISO is actually experimental and requires you to practice with different options for different environments. Also, you have to keep in mind that the above-mentioned settings may vary from one camera to another, as well as between lenses.
Next photography lessons:
Photography basics 1: Tips to Choose Your First DSLR Camera
Photography basics 3: Understanding Camera ISO
Photography basics 4: How Does Your Camera Image Stabilizer Work?
Photography basics 5: Understanding White Balance
Photography basics 6: How Your Digital Camera Sensor Works