Taking your camera out of "programmed auto" mode is one of the most significant steps you will take on your journey to becoming a better photographer. Anyone can pick up a camera and start taking snapshots in auto mode, but not everyone takes the time to master using the camera to the fullest extent of its power. No photograph will be out of your grasp if you learn how to leverage shutter speed, aperture, and ISO to your advantage.
What is the Exposure Triangle?
Exposure triangle photography is an easy way to understand the interrelationship of three crucial elements. To understand the triangle, you need to understand the individual elements of aperture, shutter speed, and ISO first.
The lens controls the aperture. Physically, the aperture is like the iris of your eye. It opens wider when there is low light and closes smaller when there is a lot of light. You can see the aperture close when snapping a photo if you look through the front of a camera lens.
But what does changing the aperture actually do to the image? If the aperture is left wide open, it lets a lot of light in. When it gets smaller, it lets less light in.
But the aperture controls more than just the amount of light. It controls focus within your image. Images taken with wide-open apertures have shallow depths of field. Only the center subject will be sharply in focus, while the background will be blurry. If the image is snapped with a small aperture opening, then more of the scene will be in focus.
Photographers measure aperture in terms of f-stops. Perhaps somewhat counter-intuitively, small f-stop numbers correspond with larger aperture openings. Therefore, a low f-stop indicates that the image will have a shallow depth of field.
Common f-stops range from f/1.4 to f/22. The limiting factor is the lens being used. While most lenses are capable of making their apertures very small, only the best lenses let enough light in to achieve f/1.4. Any lens that goes to f/4.0 is a premium example, with only the very best lenses going as low as f/2.8, f/1.8, or f/1.4. Lenses with apertures this wide tend to be large pieces of glass and very expensive.
If you want to play around with the aperture settings on your camera without messing anything else up, set your camera to aperture priority (A or Av mode). This setting allows you to set the f-stop you want to capture different depths of field. The camera automatically sets the shutter speed and ISO for you.
To understand the basics, you might want to read our Complete Beginner's Guide on Photography lighting.
The next vital factor to learn is shutter speed. The shutter is a cover that sits in front of the camera sensor. When it opens, light is allowed to hit the sensor and expose the image. The photographer controls how long the shutter is allowed to stay open.
Keeping the shutter open longer allows more light to hit the sensor. If the scene is very dark, or the photographer has set a tiny aperture, this allows the image to be correctly exposed. Doubling shutter speed will double the amount of light that hits the sensor.
Most shutter speeds are measured in fractions of a second. The most commonly used speeds range from around 1/30th of a second to 1/500th of a second. These allow for handheld images in most situations and allow enough light in to expose a normal frame. To simplify camera displays, shutter speeds that are measured in whole seconds are usually followed by the symbol for seconds, i.e., 3", 10", or 30". Fractions of a second typically omit any reference to the fraction, so a shutter speed of 1/500th of a second would simply appear as "500."
The available range of shutter speeds is limited only by the camera. High-end DSLR cameras have super-fast shutters that can snap images in as little as 1/8000th of a second. They also have "bulb" settings, which allow the photographer to hold the shutter open with a remote release for as long as necessary.
But just like aperture controls something else, so too does shutter speed. Leaving the shutter open for extended lengths of time will result in blur introduced into the images. If something is moving quickly in the picture, like a car driving by on a highway, then it will be blurry. If the camera is being handheld, slow shutter speeds can mean that the image gets blurred by your hands shaking.
Most of the time, blurry photos are to be avoided. To avoid a handshake, a good rule of thumb is always to use a tripod if the shutter speed is equal or less than the denominator of the lens' focal length. For example, if you are using a 35 mm lens, a tripod should be used for shutter speeds at or lower than 1/35th second. If using a 200 mm lens, use a tripod for speeds at or less than 1/200th second.
Sometimes blur is desirable, though, for creative purposes. Quick moving waterfalls are lovely when blurred just enough to show the motion of the water. Seascapes can be blurred to give the water a mirrorlike and smooth look. Night photographers use slow shutter speeds to capture star trails and light trails on highways.
Just like aperture, understanding how to use the shutter speed will open up new creative options in your photography. With the camera set to shutter priority (S or Tv mode), you can set a specific shutter speed, and the camera will choose the appropriate aperture.
In the days of film cameras, the film was sold in various ISOs. These were standardized sensitivities. A high ISO film, like 800, 1600, or even 3200, was very good at capturing images in low-light situations. But unfortunately, the trade-off was that the exposures would be grainy. For the best quality images, photographers stuck to ISO 100 or lower.
Very few of us use film cameras much anymore. But the terminology and concept of ISO haven't changed. Today, digital camera manufacturers allow us to set how sensitive the camera's sensor is to light. By changing the ISO setting, we can make the sensor more sensitive. But just like the film of yesterday, as ISO increases, quality decreases.
Luckily, this is an area where technology continues to improve. Every new camera sensor has slightly better performance at high ISO settings than the one it replaces. The only way to get a feel for how yours performs is to take some experimental shots and see.
Understanding How Aperture, Shutter Speed, and ISO Work Together
A specific amount of light is needed to create a properly exposed image. If not enough light is applied, then the image will appear dark, or underexposed. If too much light is let in, the image will be overexposed.
As you add light to an image by increasing the shutter speed, you will have to take it away from something else. You could either step down the aperture or the ISO. Similarly, if you want to make an image with a large depth of field, then you will need to use a small aperture (high f-stop). This small aperture won't let enough light in, so to avoid underexposing the image you will have to increase either the shutter speed or the ISO.
Practicing exposure triangle photography is an easy way to see the interrelatedness of these concepts. If one leg of the triangle gets longer, then the other two legs must adapt too. You cannot make a change to one without also changing something about the other two.
The combination of just the right shutter speed, aperture, and ISO makes up the exposure value of an image. For every correctly exposed image, there are many, many exposure values you could use. You could use a fast shutter speed and wide aperture, or you could take it with a slow shutter speed and small aperture. The results will be nearly identical in terms of exposure.
Handily, many cameras allow you to choose between these settings in programmed auto (P mode). On most cameras, turning the main selection dial while in "P mode" will allow you to select different aperture and shutter speed combinations.
Stops of Light
A stop is also an important concept in photography. It can be used when talking about any of these concepts. To go "up a stop" is to double the amount of light entering the camera, and to" step down" is to halve the amount of light.
Stops are used to connect all of the above components (shutter speed, aperture, and ISO) together with one simple unit. Each of these parameters has its own measurement, but they also all go together to form the exposure triangle. A stop gives us a common language to use.
As mentioned above, doubling the shutter speed in seconds will double the amount of light available, or raise it by one stop.
Aperture is measured in f-stops, so it works a little differently. If you simply look at the area of an open aperture, then if you double that area, you will be going up one stop. But when it comes to f-stop numbers, doubling of the f-stop will equal a quadrupling of the light. The best way to memorize the useable stops of light in f-stops is to use an exposure triangle chart that lays out common f-stops, like f/2.0, f/2.8, f/4.0, f/5.6, f/8.0, f/11, f/16, f/22, and f/32. Once you've seen and used these numbers a few times, they will become second nature.
ISO stops are straightforward, much like shutter speeds are. Most camera ISO settings start at 100 and range up to 6400 or higher. For each doubling in the ISO value, the amount of light doubles and goes up one stop.
Stops are often divided into halves or even thirds for better control of an image's exposure value. While the numbers used in the examples above are pretty much industry standardized numbers, fractions of stops are often rounded up or down by manufacturers. The numbers might not match exactly, but the concepts are the same no matter what type of camera you use.
Examples and Analogies
If you're still having trouble visualizing how the exposure triangle chart works, consider this analogy. An image is like a glass of water. Making a properly exposed image is much like filling the glass up from a tap.
The size of the glass you must fill is an example of the camera's ISO setting. A larger glass would require more water to fill it, while a small one requires less. Much like the ISO, the size of the glass is usually one of the first things you determine. Most of your time, you will be more worried about the next two variables.
How much you open the tap, or the amount of water flowing out, is analogous to the camera's aperture. Does the water trickle out of the faucet, or does a lot of it flow out quickly?
Finally, the amount of time you leave the tap open is like the shutter speed. If you only open the tap a bit and let the water trickle, you will have to leave it open for a long time to fill your glass. Alternatively, if you open the tap all the way for maximum flow, then you only need to leave it open for a short second.
In this example, over or under filling the glass is like under or overexposing the image. Neither is desirable; your goal is to get the glass precisely full. If you change one thing, like how far the tap is open, you must immediately change how long it is open.
Applying What You Know
So how does knowing about the triangle help the average photographer? For one thing, understanding that all of these concepts are linked together means that you'll know the consequences when you need to change one of them.
Let's look at a problem that a lot of people have. Many new photographers are aggravated to find that images taken in dimly lit places come out blurry. Perhaps it is because the subject moved, or maybe it's because the camera was handheld and shaken while snapping the photo.
The solution to the problem should be clear—the shutter speed needs to be faster. But the shutter speed is related to the aperture and ISO, which means that something else is going to have to change. If shutter speed alone is increased, then the image will be underexposed. To properly expose the photograph, the aperture will need to be widened. If the aperture is already as wide as it will go, the only other choice will be to increase the ISO.
A camera isn’t the only equipment you’ll need to click a picture. You need to be aware of the photography terms and their meanings.
Exposure triangle photography might seem like a boring topic, a little too reminiscent of high school geometry class. But the concepts are relatively easy and straightforward once you pick up your camera and start playing. Understanding these concepts will open up new options in your photography, and empower you to capture scenes that were previously out of reach.
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