Exposure time, Aperture and Light sensitivity are different words for shutter speed, aperture and ISO respectively. The art of photography lies, among other things, in finding the right balance between these three settings. By playing with these three lighting elements you can achieve different results.
Originally, "exposure" had a quite literal meaning: photographic film is light-sensitive, so to take a photo you simply expose the film to light for a short time, a process that results in a photo. Simply put, exposure is the image recorded when the camera's shutter opens, exposing the film, and now a camera's image sensor, to light.
So there are three primary variables that come into play when creating a recording. These three variables together are called the 'exposure triangle' because they are all equally important and each influence exposure in a different way.
Shutter speed
Shutter speed refers to the length of time the camera sensor is exposed to light. It is measured in seconds or fractions of a second. A slow shutter speed (e.g. 1 second) lets in more light, which is ideal for low-light situations or for creating motion effects, such as blurring flowing water.
A fast shutter speed (e.g. 1/1000 second) freezes movement, perfect for capturing fast action such as sporting events. That very short time is enough for the image sensor to take and record the photo, provided the other two variables are adjusted correctly.
The amount of time the shutter remains open also affects how an image looks. For example, very fast subjects shot at very fast shutter speeds look frozen in time. Even water droplets can appear razor-sharp in the air, provided you choose a shutter speed fast enough to capture them that way.
On the other hand, if you use a slow shutter speed, you will capture motion blur. Sometimes this is undesirable, but motion blur can also be used creatively. For example, very slow shutter speeds can capture star trails or light trails from cars, which appear as long streaks in the final image. This can add a lot of creativity to taking a photo.
Long shutter speeds are only a problem if there is movement in the shot and/or if you have not mounted your camera on a tripod. Trying to hand-hold the camera during a long exposure can cause "camera shake," or visible blur caused not by the movement of the subjects, but by the movement of your hands. If the camera is mounted on a tripod, you can use long exposures on almost any stationary object, but anything that moves will still appear out of focus, even when the camera is stabilized.
Diaphragm
The aperture (or aperture) is the opening in the lens that can be increased or decreased to control the amount of light reaching the sensor. Aperture is indicated by f-numbers, such as f/2.8, f/8, etc. A small f-number means a larger opening and more light, while a large f-number indicates a smaller opening and less light.
Aperture differs from shutter speed in that it is related to the size of the opening through which light reaches the sensor, rather than the amount of time the sensor is exposed to that light. So with a larger aperture you can take photos in low light, and with a small aperture you can take photos in bright light, but there is much more to it.
With large apertures (low f-number) you can use fast shutter speeds, because with a large aperture you need less time to get the necessary light onto the image sensor. Small apertures (high f-numbers), on the other hand, require relatively slow shutter speeds for the opposite reason: generally less light passes through that opening, so the shutter has to stay open longer.
Aperture also has an additional, but extremely important function: it controls the depth of field in a photo. Depth of field is a term you've almost certainly heard, but if you're new to photography, you may only have a vague idea of what it means.
Simply put, depth of field is the amount of the photo that remains in focus. A larger aperture (smaller f-number) provides a shallower depth of field, blurring the background and putting the focus on the subject.
• Large aperture: A photo with a shallow depth of field may have an area of just a few centimeters with very sharp focus.
• Small aperture: A photo with a large depth of field can have sharp focus from foreground to background.
ISO
The third element in the exposure triangle is ISO. ISO is the sensitivity of the camera sensor to light. A lower ISO value (e.g. ISO 100) is less sensitive and ideal for bright conditions. A higher ISO (such as ISO 3200) is more sensitive and better suited for low-light situations, but may lead to more noise or grain in the photo.
ISO is actually an old term and stands for 'International Standards Organization'. The term comes from the early days of film, when there was no standard for how light-sensitive film manufacturers would make their product, so photographers really had no easy way to know which films were suitable for low light and which films would be better. Fortunately, in 1974, light sensitivity was standardized across all film brands, which meant that a roll of Kodak 100 was roughly equivalent to a roll of Fujifilm 100, at least as far as light sensitivity was concerned.
The term is still used in digital photography to describe light sensitivity. Nowadays you don't have to roll of film can be changed to change the light sensitivity; you simply change the setting in your camera's menu system. That means you can make one setting in very low light and then go outside and use the next frame to shoot a sunny landscape.
What matters to you is how ISO affects an image. You already know that this makes your camera more sensitive to light, so one of the most valuable things you can do with it is take photos in low light without using a tripod. High ISOs can also help you achieve a fast shutter speed in semi-bright conditions, which is important when you're trying to capture very fast action in less than optimal shooting conditions.
But high ISOs also have disadvantages, especially with older camera models. When you set the ISO too high, you can get digital noise in the photos, which manifests itself as a kind of sandy or grainy texture.
Very high ISOs can produce images with long discoloration streaks and noise and appear grainy. Less obvious are the problems that high ISOs can cause with color and tone, which can appear increasingly muddy or ill-defined as the ISO increases.
But this is actually a bigger problem for older camera models; new models can handle high ISOs very well and you may not be able to easily tell the difference between a photo you took at ISO 400 and a photo you took at ISO 3200.
Practical tips for beginners
Start with auto mode: If you're just starting out, experiment with your camera's automatic mode first. This helps you get a feel for how the camera determines exposure.
Practice with one setting at a time: Try experimenting with one setting first, such as just the shutter speed, while keeping the other on auto. This helps you understand how each setting affects the photo.
Use the ISO: Don't be afraid to play with the ISO. Modern cameras have excellent capabilities at higher ISO values, giving you more flexibility in different lighting conditions.
Pay attention to motion blur and noise: Slow shutter speeds can cause motion blur and high ISO values can cause noise. Be aware of these effects and how to minimize them.
Conclusion
You can think of an exposure as the end result of the different ways your camera presents light to the image sensor. First, there is the size of the aperture, or the opening between your lens and the image sensor. Then there's the length of time light is allowed to pass through the aperture, and finally there's the image sensor's overall sensitivity to the incoming light. These three factors together determine the exposure, or the image that you capture in pixels.
Also read: From auto mode to M mode: photographing with the Sunny 16 rule
