How To Understand Photography Exposure
Don Orkoskey | March 15, 2023
Learn how to understand photography exposure to correct issues of brightness in your photography. A fundamental part of understanding photography is controlling your exposure.
In this article we're going to explain what exposure is and then talk about the three ways we can control exposure which are:
What is Exposure?
In photography exposure is simply the level of brightness in our pictures. We can control our exposure by adjusting the amount of time and volume of light that strikes our sensor. Additionally, we can adjust how sensitive our sensor is to that light. These three settings give us full control over our exposure.
People generally get confused with exposure settings but understanding exposure is not as complicated as you may believe it to be. Again, exposure is simply the amount of brightness in our photographs.
If we can remember that all we're doing is controlling brightness we can find our way through the problems we're facing.
Let's break down the three options we have for controlling brightness. By discussing them one-by-one. In doing so we can begin to use these settings more purposefully. Additionally, we'll experience less frustration.
Controlling Exposure With Time
The first tool we'll discuss for controlling exposure is time. In photography we measure time in seconds or fractions of a second. Simple enough right?
Measure Time In Fractions
Let's look at how photographers measure time in fractions of a second. It's simple to understand that one second is twice as long as one-half-of-a-second. Too you can easily understand that one quarter of a second is half as much time as a half second. With that being the case the amount of brightness at a half-second is twice as much brightness than at a quarter-second.
We taking photos we typically use much smaller fractions of time but it's important to remember that we are doubling or halving the brightness each time we double or half the amount of time. Equally important to remember is that, with fractions, the larger the denominator (bottom numbers) is the less time we have. This is usually where we get confused.
Since the fractions we use in photography always have a one (1) as the numerator (top number) we usually just use the denominator. You'll see this in your settings. Rather than your camera saying 1/250th (of a second) it will usually simply say 250.
The time that we control when making a photographic exposure is called our shutter speed. We call it that because our shutter is a mechanical (or electronic) device inside our camera which keeps this time accurate. When we say, "I need more brightness so I must decrease my shutter speed." What we mean is that to add brightness we're going to need to add time.
We can add time (and brightness) by changing our shutter speed.
Q. If our shutter speed was 1/500th of a second, and we need to add brightness, would we change it to 1/1000 or 1/250th to add light?
A. Because we need brightness and therefore are adding time a 250th of a second is twice as much light. Whereas a 1000th of a second is half as much.
Remembering that the bigger the number the lower the amount of time can be really challenging. Don't get flustered if this happens to you. This is the most common issue people learning photography face. You're far from alone in struggling with this.
Control Exposure With Volume
Just as with time when we control exposure with volume we often double or cut in half the amount of light. Lenses are simply tubes, fitted with shaped pieces of glass which direct the light to our sensor (or film). The larger the opening in the lens where light can pass through, the higher the volume of light.
Measuring the Volume of Light
We measure the volume of light by the size of the opening in our lens. We call this opening our aperture. This aperture is adjustable on most cameras. However, on smartphones and some less expensive cameras it may not be.
Setting our aperture is how we control the volume of light.
Just as with our shutter speed our aperture is a measured in fractions. It's a fraction of the focal length divided by the the diameter of the "entrance pupil" - simple right? Of course not. The important thing is knowing that it's a fraction. Even many long time photographers can't remember what it's a fraction of exactly.
Understanding f Stops
We not only call our aperture, aperture. You will also hear the settings themselves called f-stops. This f is used because they're a fraction of the focal length and we stop at those fractions.
Understanding Aperture and Exposure
The challenge we face when trying to understand aperture and exposure relates to Pi. Whereas with our shutter speed we can understand that a 2000th is half as much light as a 1000th of a second, aperture is a bit trickier. Aperture is dealing with circles and therefore Pi. This means the numbers don't look twice as big or half as small. Our aperture may include the following set of numbers:
4, 5.6, 8, 11, 16, & 22
Those numbers allow in half or double the amount of light but they're hard to intuitively understand. Blame this on Pi.
Controlling Exposure with Time & Volume
Because both our shutter speed and aperture double or half the brightness we can control our exposure easier with both time and volume.
It often happens that the level of brightness will be correct but we can have blur or other issues. These issues can be resolved by changing one setting and then compensating for that change with the other.
My exposure settings are:
1/15th of a second and f22. I'm photographing a soccer game and the brightness is correct. However, the players are all blurry from running. I need to increase my shutter speed to freeze their motion. By changing my shutter speed to 1/250th I can freeze their motion. However, doing so made cut my brightness by a bunch. I can get that brightness back by adjusting my aperture.
Because I changed my shutter-speed by 4 "stops" I need to change my aperture by 4 in the other direction. In other words, I took light away and now I need to add it back.
Q. What is my new aperture going to be?
A. It's 4 stops brighter so we need to go from f22 to f5.6
Does that make sense to you? If not, spend some time trying to understand it. If you're still stuck then read the following breakdown.
Our original settings were: f22 and 1/15th of a second. We changed our shutter speed to freeze the motion. In order to freeze the motion we needed a shutter speed of a 250th of a second. We went from 15 to 30, 60, 125, and stopped on 250. That's 4 stops. Don't let the math mess you up. We changed our shutter speed by 4 stops. Our exposure got darker. Now we need to bright that light back by changing our aperture 4 stops. It's as simple as that. Therefore, we went from f22 to, 16, 11, 8, and stopped on f5.6.
Controlling Exposure With Sensitivity
The final way we can control our exposure is by changing the sensitivity of our sensor. We can make our sensor more or less sensitive to light. When we make it more sensitive it needs less light to achieve the same level of brightness.
Double or Half Our Sensitivity
Just as with our shutter speed and aperture we can double or half the sensitivity of our sensor. We measure these changes in ISO. If you see a setting in your camera called ISO that is your sensitivity.
Many cameras come pre-set to Auto-ISO these days. If yours is one of them then you won't be able to adjust the brightness without first changing this. With auto-ISO turned on you can add and subtract time or volume all you want but the camera will adjust the ISO and therefore your brightness won't ever change.
Take Control of ISO
Take control of your ISO to adjust the brightness. There's nothing wrong with using auto-ISO or any other automatic settings. Additionally, setting some of these controls to auto can be incredibly helpful. Check out this article I wrote about exposure compensation when you're ready to find out more. That said, when we take control of our ISO we can adjust the brightness ourselves rather than relying on the camera to do it for us.
You Now Understand Exposure
Congratulations, you now understand exposure. Or at least, you understand the settings that help us control it. to find out more be sure to subscribe to our free monthly newsletter. You can also check out other beginner articles here. Good luck with controlling your exposure and advancing your pr