Learn the Fundamentals of Exposure in 15 Minutes or Less
- ISO refers to your camera sensor’s sensitivity to light. Each ISO number represents a stop of light, with higher values representing greater sensitivity to light. Each increase in stop, say from 100 to 200, represents a doubling of the light sensitivity.
- Aperture refers to the size of the opening in the lens and determines how much light reaches your camera’s sensor. Aperture values are represented by f-numbers, which have an inverse relationship with the size of the aperture opening. So, a small aperture number, like f/2.8, represents a very large aperture opening. A large aperture number, like f/22, represents a very small aperture opening.
- Shutter speed refers to how long the shutter remains open. Shutter speed is measured in fractions of a second, so a shutter speed of 1/125 seconds means the shutter is open for less time than when a shutter speed of 1/30 seconds is used.
Exposure is one of the more technical aspects of photography, but just because it’s a complex topic doesn’t mean that it has to be difficult to learn. In fact, if you aren’t sure how to control exposure, just dive into this lesson and in 15 minutes or less, you will have a much better understanding of what exposure is and how to manipulate it. Then you will have better pictures to show for it too!
Quick Overview: Elements of Exposure
There are three elements that control exposure: ISO, aperture, and shutter speed. Together, they are referred to as the exposure triangle, seen above.
When these three elements are combined, they give you an exposure value (EV). A change in one element will have a direct impact on the other two elements and result in a changed EV, and by default, an image that looks different as well.
Let’s consider an example. If you start out with an ISO of 400, an aperture of f/8, and a shutter speed of 1/30 seconds, but find that the image is overexposed (too bright), speeding up the shutter to a speed of 1/125 seconds would darken the image. Why? Because the shutter would be open for less time, thus allowing in less light.
Here’s another example. If your ISO is set at 100, your aperture at f/16, and your shutter at 1/15 seconds, but have an image that is underexposed (too dark), opening the aperture to f/11 will lighten up the image and get you a better exposure. Why? An aperture of f/11 has a larger opening than an aperture of f/16, thereby allowing in more light into the lens and resulting in a more properly exposed image.
An Exposure Metaphor
With the basic review out of the way, let’s use a metaphor to help you better understand exactly how ISO, aperture, and shutter speed work together to influence exposure.
Think of your camera as being your brain, and the lens as being your eyes. Your eyes (lens) see things out in the world, but by themselves cannot record what they see. So, your brain (camera) does that for you.
If, for example, you’re looking at the wasp above, your eyes see that it’s black and yellow and that it’s feeding on an orange flower, and that information is sent to your brain to be recorded. But, if you look at the wasp too quickly, that information would be less complete. If we apply that situation to your camera, looking at the wasp too quickly would result in an image with an exposure that’s off because an exposure that’s too dark or too light occurs when the information being sent to your camera is incomplete, like so:
In the image above, there isn’t enough light, so the image is underexposed.
Conversely, if you let in too much light, the image will be overexposed. Both underexposure and overexposure result from something being off in the relationship between ISO, aperture, and shutter speed.
Think of ISO as Night Vision Goggles
It might be easiest to think of your camera’s ISO setting as being a pair of night vision goggles.
The higher the ISO, the more sensitive your goggles are to light, and the better you can see at night. For example, when you’re taking photos indoors at night, you’d need your goggles to be more sensitive because of the reduced amount of light. Therefore, you might use ISO 1600 so you can see. On the other hand, if you’re shooting photos outdoors at mid-day you don’t need your goggles on at all, and would use a small ISO, like ISO 100, because there is plenty of light for you to see with already.
Think of Aperture as Your Eyelids
As mentioned above, your camera’s lens is like your eyes, so the aperture would be like your eyelids. A small aperture value, like f/2.8 (which, if you remember, is a large aperture opening) would be like your eyelids being wide open.
Conversely, a large aperture value, like f/22 (which is a small aperture opening) would be the equivalent of you squinting.
Think of Shutter Speed as Blinking
If you were having a staring contest, your shutter speed would be super slow, like 1/60 seconds. But, if you are outside on a bright, sunny day without sunglasses, your shutter speed would be really fast, like 1/1000 seconds. Naturally, the longer you go without blinking, the more light that enters your eyes. The same thing applies to your camera, so if it were really bright, you’d use a faster shutter speed. If it were dark out, a slower shutter speed would be needed to get the right exposure.
Final Example
Let’s say you’re in your backyard at dusk and you want to photograph your dog. Since the sun has already set, you’d need to use your night vision goggles (ISO) so you can see better. A medium setting like ISO 800 would probably do the trick. Again, because there isn’t much light, you would need to open your eyelids (aperture) pretty wide. A small aperture value (large aperture) of f/2.8 would be in order. Lastly, you would want to keep your lens from blinking too much (shutter speed), so a slow shutter, like 1/30 seconds might be needed.
Conclusion
Armed with the information presented in this article, you should have a better understanding of the elements that influence exposure. Just remember that ISO is like night vision goggles, the aperture is like your eyelids, and shutter speed is like the speed with which you blink, and you should be able to remember what each element of the exposure triangle is responsible for doing. Now it’s just a matter of putting your camera into manual mode and applying what you’ve learned to take images that are properly exposed!