What is exposure in photography?
Exposure is the amount of light that goes through your camera’s image sensor or in the old days of photography, the film. It not only dictates the brightness, but also the looks of your photographs.
We can regulate it using our camera’s three main exposure controls:
- Shutter Speed
Each of these controls has inherent effects on our image aside from the brightness. And they all work together to form the final rendered image.
To be clear though, only the aperture and shutter speed affects the actual amount of light that reaches the image sensor (or film). ISO works a little differently which we’ll discuss a little later.
Understanding the concept of the exposure triangle is a great way to quickly grasp the relationship between these 3 controls. We highly recommend checking out that post as well.
Why is it important?
Aside from the fact that exposure affects what we see in the image, digital cameras also have a limited amount of data it can store.
When you exceed this limit, you will never get details back. And yes, even if you adjust the exposure on image processing software like Photoshop or Lightroom.
If you do not plan to edit the photos, then it is even more important to pay attention to the exposure since you’ll pretty much get what you see.
If you shoot in RAW, you will have a much better leeway in terms of preserving those details. However, this limitation will still exist even if you have the best camera in the world.
This limitation is called the dynamic range which kind of deserves a post of its own.
Anyway, having too much light will make our image overexposed. In turn, we may lose some details on the brightest part of our image like the sky for example.
We also do not want our image deprived of light. An underexposed image may lose some details in the darkest portion of the image.
Ideally, we want to aim to get proper exposure with each shot by controlling the camera’s exposure controls.
How to control the camera exposure:
First off, there is no universal setting for proper exposure. It all depends on the actual light in the scene you are photographing.
What we can do, is regulate the light coming to our sensor based on the amount of light already in the scene.
To do that, we’ll have to understand what exactly does each of the exposure controls does to our image:
Aperture relates to the iris opening in your lens. The wider the iris opening, the more light passes through.
It is usually represented by “f-stops” which is a representation of how big or small the iris opening is.
One thing that’s a little confusing at first is that lower f-numbers mean the hole is bigger. That is because f-stop is a mathematical equation that measures the ratio of focal length over the diameter of the hole of the lens.
So f/2.8 is bigger than f/4.
But that’s not all it does.
Aperture also affects the depth of field.
The depth of field is the amount of in-focus area in your image.
Having a wider aperture gives you an image with a shallower depth of field. While narrower aperture gives you a deeper depth of field.
In other words, lower f-stop numbers (bigger aperture) give you more background blur and less sharp (in-focus) elements. While higher f-stop numbers (smaller aperture) give you an image with more in-focus elements. Or lesser background blur.
Have a look at this example:
Check out the action figure at the back. You’ll notice that it becomes sharper as we adjust to a higher f-stop number(narrower aperture).
It is worth noting that it is more difficult to keep subjects in-focus with wider apertures. Due to the smaller depth of field, some parts of your image may already be out of focus if you are not careful.
We created a post that discusses the practical ways to control depth of field. It will give you information like how it is perceived and what other factors that can affect it. We suggest that you check it out as well.
Shutter speed is the amount of time it takes for your camera to capture an image.
The faster the shutter speed, the less light your camera can accumulate. This results in a dimmer image.
Examples are 1/30th, 1/60th of a second, etc. But it can also go as slow as 1-30 seconds for most cameras.
There is also an option for bulb mode which lets it open for as long as you hold down the shutter release button.
Keep in mind though that shutter speed also affects motion blur. The slower it gets, the more motion blur you get from the image.
Using a fast shutter speed freezes the movement of your subject.
This lets you capture moments you would otherwise miss. Like a jump shot or a bird in flight for example.
The downside is, you will be letting in less light.
This can play to your advantage if you have too much light in the scene you are photographing. Like shooting outdoors at noon for example.
But there are times you may want to open the shutter longer than a fraction of a second for artistic purposes.
Long exposure shots, for example, will need a shutter speed setting for 1 second, 30 seconds or even for a couple of minutes. The goal is to record every single movement created during the time the shutter is open.
When applied properly, it can help you capture surreal pictures.
But be careful, using a slow shutter speed without proper stabilization may cause camera shake that can make your shots blurry and unsharp.
We created an in-depth post about this topic. It includes how to pick the best shutter speed for your image.
The same as the other two exposure controls, increasing the ISO lets you capture a brighter image but with a little drawback. Increasing ISO too much will also increase noise.
Technically, it does not increase or decrease the amount of light you already gathered. It simply amplifies the light you gathered through aperture and shutter speed.
Think of ISO as a microphone. Except that you can’t turn off the sound completely.
You can amplify the music that is actually heard by turning the volume up or down.
A barely audible voice can still be amplified to acceptable levels by raising the volume. But you’ll hear a lot of static noises if you raise it up too much.
In this scenario, it would be better to speak louder instead of needlessly increasing the volume right?
So if you need more light, try opening up your aperture or slowing down your shutter speed first.
For this reason, I’d suggest keeping the ISO as low as you can, whenever you can.
I’m not saying that you should totally ignore the ISO dial though…
On the contrary, keeping the ISO low when you actually need to crank it up will do you no good.
There’s a limit on how far you can adjust your aperture or shutter speed just to get a proper exposure. Let me give you an example:
For artistic purposes, you might want to use a small aperture so you can have a deep depth of field. This, in turn, can help you create an image where everything is sharp from front to back in exchange for dimmer images.
Or you want to keep the shutter speed super fast so you can capture that amazing kickflip in the air.
In both of these examples, you probably don’t want to change one of the exposure controls at all cost.
So when you reached that limit, ISO is the way to go.
Keep in mind that a good exposure captured in-camera is better than adjusting an under or overexposed image on an image processing software.
Our beginner’s guide to ISO will help you know more about this topic.
Exposure Value (EV):
The combination of aperture, shutter speed and ISO is called the exposure value.
There is no definitive rule on which control you should adjust when trying to get the proper exposure. You can either adjust your ISO, shutter speed, aperture, just two of them or all three and still arrive at an image with balanced brightness.
But here lies the problem of some sort…
You can have 2 different combinations that yield the same exposure value. Have a look at the image below:
If there are no rules, then how do we know which of the controls should we change?
To begin, we shouldn’t look at exposure with only the brightness in mind. As mentioned earlier, each exposure controls also affects the aesthetics of our images.
Instead, we should do the adjustment based on the end goal we have in mind.
Having said that, we should also consider the look, feel and even the color accuracy we want to have for our final (jpeg, png, webdp export or physically printed) image.
Say, for example, your goal is to create an image with a shallow depth of field.
You will want to set your aperture at the widest setting (lower f-stop number) and keep it that way. If the light is lacking, you will then adjust the shutter speed or ISO to compensate for the lack of light.
How to measure exposure increments: Stops
It’s all good and well, but how exactly do we know how much adjustment we need to arrive at a good exposure?
Good thing, the pioneers of photography came up with a system called stops. It can be used to somehow quantify the exposure value you are adding (or subtracting) when you adjust either the aperture, ISO or shutter speed.
On most cameras, the default increment is 1 stop. For example, if you move your shutter speed dial one time, you are adding 1 stop of light.
Adjusting “1 stop higher” means doubling the amount of light going to your sensor. And as you can guess, “1 stop lower” means you are cutting the amount of light by a half.
I want to make it clear that “stops” and “f-stops” are different terms. F-stop refers to the approximate opening of your lens’ iris and therefore only relate to aperture.
While “stops” refers to the approximate amount of light you are letting in through the combination of aperture, shutter speed or ISO. So if you say “adjust it 1 stop higher”, you can do it by adjusting either shutter speed, aperture or ISO.
Let’s have an example scenario:
Say, that this setting is a good exposure in terms of brightness:
Shutter Speed: 1/60th
However, the image has too much noise! So naturally, you want to bring down the ISO as much as you can.
The problem is, the image will be underexposed if you don’t use a higher ISO.
You can compensate for the lack of light by adjusting your aperture 1 stop up to double the amount of light.
So instead of the settings above, you will use these instead:
ISO: 800 — Cut in half (adjusted 1 stop lower)
Aperture: F/2.8 — Doubled (adjusted 1 stop higher)
Shutter Speed: 1/60th — no change
But what if it still has a lot of image noise?
Well, consider adjusting your aperture 1 more stop up or adjust your shutter speed 1 stop slower. So you can use lower ISO.
You can do this over and over until you arrive at the base ISO and still have a good enough brightness for the image. Just don’t forget your shutter speed and aperture limitation I’ve mentioned earlier.
At this point, we pretty much have the information we need to fully control the camera’s exposure at will.
Hence, we can now easily understand what happens to our exposure when we leave it in automatic mode.
Exposure Compensation and Camera Shooting Mode:
Exposure compensation is a feature in your camera that lets you adjust the exposure value (EV) on the fly without touching the exposure controls individually.
Basically, if the image is too dark or too bright, you just adjust the exposure compensation to +1 EV and vice versa.
It changes either the aperture, shutter speed or ISO based on the Exposure Value you dictated to add or subtract.
Which control exactly? It depends on what shooting mode you are currently in.
Here are the most common shooting modes:
- Automatic Exposure – As the name suggests, you essentially let the camera decide what it thinks the best combination of exposure setting is for the current shooting condition.
If you use exposure compensation in this mode, you have no control over your exposure settings whatsoever.
Using it at this mode isn’t very reliable as you never really know what setting it will change.
- Program Mode (P) – This is a semi-automatic mode that gives your camera control over the aperture and shutter speed.
Basically, out of all the exposure controls, you can only change the ISO. You can also change other options such as white balance or firing the flash, but that’s really out the topic of this post.
Using the exposure compensation in this mode will change either the aperture or shutter speed. Unless you use auto ISO, making it pretty much the same as auto exposure.
This is great if you’re just starting out and really don’t know what settings to use. But in terms of control, this one is still not very reliable.
- Aperture Priority – Like program mode, it is a semi-automatic mode. The great thing is, you get to pick the aperture and leave the shutter speed up to the camera.
In this mode, using the exposure compensation will only change the shutter speed. Making this a pretty reliable option when you are shooting in a hurry.
I wanted to quickly note though that if you are set to auto ISO, it will either change the shutter speed or ISO. Whether this is a good thing or not probably depends on the light available at the scene you are shooting.
- Shutter Priority – This mode is like the opposite of aperture priority. Basically, you only get to pick your preferred shutter speed setting. And the camera will take care of what it thinks the best aperture to use.
And likewise, using the exposure compensation will only change the aperture unless you are using auto ISO.
- Manual Mode – We, ourselves, pick what we think is the best aperture, shutter speed and ISO setting in this mode.
Using the exposure compensation will not do a thing in this mode unless we are using auto ISO. In which case, the only thing it can change is the ISO.
Auto bracketing is another feature on most DSLR and Mirrorless. Turning on this feature will make your camera take 3 or more shots in a row every time you press the shutter release.
Each shot will have different exposure values. The stops difference will depend on your settings.
For example, you set it to take 1 stop under and 1 stop over your current exposure value. You can even use it to increment 1/3 of a stop at a time and take more than 3 shots if you wish.
But why take 3 pictures with 3 different exposure value in the first place?
Remember about the dynamic range limitation I’ve mentioned earlier?
Sometimes, the scene we’re capturing has such a high dynamic range that it is pretty hard to tell if we are actually getting the right exposure.
Getting the 3 exposures for the same shot will give us some sort of back up just in case we missed something in the highlights or shadows.
You can even blend these images together in Photoshop so you can have a very high dynamic range photo. Even though you exceeded your camera’s limitation.
We’ll be creating a post on how exactly we do this. Make sure to subscribe to our list and get a notification once it’s up.
Understanding exposure is something everyone interested in photography should know.
It will not only help you pick the right camera settings in terms of brightness but can also change the overall appearance through depth of field, motion blur and noise levels.
Plus, knowing how it works can greatly speed up your image-taking process. This is by utilizing camera features such as shooting modes, auto bracketing and exposure compensation.
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