The Exposure Triangle is one of the most important but for many difficult to understand principles in photography. The good news is, - it is easy to learn.
The Exposure Triangle is a simple way to explain the relation between exposure, aperture, shutter speed and ISO and how these settings determine the correct exposure value. As soon you understand how exposure works you have endless possibilities in photography.
You might have heard about aperture and shutter speed. But do you know what they actually do? If you don’t know, you should read this article first.
The tree settings play an important role, and they are closely linked to each other. If you change one setting, this will influence on the other two settings.
Exposure value
A given combination of aperture and shutter speed will represent a specific Exposure Value (EV). For any light situation, there is a correct Exposure value. What is great about this and maybe the confusing part, there is more than one combination of aperture and shutter speed giving the same Exposure Value.
Your creativity and how you want a photo to look like decides which combination you should use.
In the image below you can see which Exposure values you can expect in different light situations.
As you see, the EV scale is wide, and it can be extended even further. Photographing with the sun in the frame will result in an EV value higher than 16. Shooting stars at night will result in an EV value below -3.
The best cameras on the market are capable of covering a range of 12-13 EV’s on this scale. How many EV's a camera is capable of covering in one exposure is referred to as the cameras dynamic range.
As a comparison, the human eye is capable of adjusting, so they cover a range up to 20 EV’s on this scale.
The water bucket analogy helps you understand the Exposure triangle
Correct exposure
Exposure is about collecting the correct amount of light on a camera sensor. If you collect too much light, you will overexpose (image too bright), and if you collect too little light you will underexpose (image too dark).
Imagine exposure as you were collecting rainwater in a bucket. When the bucket is full, it represents a correct exposure.
Available light
Light is a fixed value depending on the conditions at the time you shoot. You need a certain amount of light to hit the camera sensor for a properly exposed photo. Think of the light as rain. Heavy rain is comparable to a lot of light while drizzle is little light.
Shutter speed
Shutter speed is how long you need to keep the bucket in the rain to fill it. If it’s only drizzling, it will take longer time to fill. In the camera analogy, this is a low light situation requiring a longer shutter speed to get the correct exposure.
Obviously with heavy rain it takes shorter time to fill the bucket. Similarly with a lot of light you need a shorter shutter time for the correct exposure.
Aperture
Aperture represents how wide the opening of the bucket is. Now let us imagine we put a lid on the bucket covering half of the opening. With only half the opening, you will need the bucket to stand in the rain double as long time to fill it.
Similar, if you choose a smaller aperture (opening) on your lens (bigger f-number), you will need a longer shutter speed for the same exposure.
ISO
ISO represents the volume of the bucket. If you use a smaller bucket, let us say half the volume, you have two choices. With the lid completely removed you must leave the bucket for half the time to fill it.
The second option is you can use the lid and cover some of the opening of the bucket. With the lid on you can leave the bucket for longer time in the rain.
However changing the size of the buckets all the time is unpractical. You want to stick to the “standard” bucket. The same for ISO, you don’t want to change the ISO unless necessary. You should always keep the ISO lowest your camera allows. This way you ensure the best possible image quality.
How long it will take to fill the bucket depends on:
- how much it is raining (available light)
- how much of the lid is covering the bucket (aperture)
- how long you leave the bucket outside in the rain (shutter speed)
- the volume of the bucket (ISO)
Based on the above, which factors are in your hands to control? Everything except the light, right? In landscape photography, you have very few possibilities to control the light yourself. Therefore, you must adjust the other parameter to properly “fill up the bucket”.
The Exposure Triangle
The Exposure Triangle makes it easier to see how aperture, shutter speed, and ISO relate to each other. Let’s see how each of these parameters can be used in your photography.
On each of the tree sides of the Exposure Triangle, the numbers on the scales are equally distributed with one f-stop between each. If you change one the sides up or down, you will have to compensate the same on any of the two other sides.
The grid indicates all the possibilities you have to combine aperture, shutter speed and ISO for the desired exposure.
ISO - the setting you should avoid adjusting
For the purpose of the Exposure Triangle, the least important of the tree settings is ISO. Changing the ISO itself will not give you any creative options. The only exceptions are if you by purpose want noise or grain in you photos.
But if you want to simulate old film grain I suggest you shoot a regular photo and add the grain in Lightroom or another imaging software later. This way you have your “untouched” original as well in case you change your mind later.
You can think of ISO as a “last opportunity setting”. If you after adjusting aperture and shutter speed still don’t get the exposure you want, you can increase the ISO to get more light on the camera sensor. Basically, this will be in low(er) light situations. How wide the ISO scale is, is limited by your camera.
Creative use of aperture - not so much in landscape photography
In landscape photography aperture is important for one purpose, getting as much of the scene in focus as possible. This is a challenge landscape photographers meet most of the time.
Aperture is closely related to Depth of Field. If you’re not after any particular creative effects and the light conditions allows, you will want to set the aperture at the lens "sweet spot”. Read more about other lens features here.
If you purposely want some of the scene out of focus, you choose a wide aperture like f2.8 of f4 if your lens allows for it. At a given distance to the subject at constant focal length, the smaller aperture you choose (bigger f-number), the more of the scene will be in focus.
If you need to stop the lens all the way down to f22 for sufficient Depth of Field, do it. Some photographers avoid using the smallest and biggest possible aperture of the lens because the image sharpness is not optimal. But isn’t it better with a slightly less sharp image than not getting the image at all?
On the Exposure Triangle, the aperture scale is limited by the lens you use. You can only work with the apertures available on the lens, no more no less
Creative with shutter speed
For me, shutter speed is the most fun and “creative” setting I have on my camera. I use and play with shutter settings a lot, longer shutter times. Creative use of shutter speed is the easiest one to recognize in a photo. When clouds are blurry, waterfalls are white and silky, star are moving on the sky you know this is the use of long shutter speed.
For landscape photographers, long exposure photography is important, and you will see a lot of images shot at long shutter speeds.
On the other end of the shutter scale is the extreme short shutter speeds. Short shutter speed is used when you want to freeze motions. In landscape photography, extreme shutter speed is not required very often. The fastest moving objects in landscape photography is probably moving water(fall).
On the Exposure Triangle as I already mentioned, both the aperture and ISO have a fixed scale depending on the camera and lens you use. When you have reached the far end of these two scales in any direction, you cannot do more.
The shutter speed, however, has no limit in the longer end of the scale. This is what makes shutter speed so fun. Even if your camera says a maximum shutter speed of 30s, you can go way beyond that in Bulb mode (B). Most cameras have the bulb mode available.
There is one limitation with this extreme long shutter speeds; you will need a tripod. Without a tripod, you will not be able to enjoy the creative aspects of long exposure photography.
Actually you will only be able to use a fraction of the shutter speed scale is you shoot handheld. I can only say one thing, get yourself a solid tripod. The sooner, the better.
Practical use of the Exposure Triangle
Too much light is rarely a problem in photography. The exception is if you want to use long shutter speeds during daytime. It is too little light that most often is the challenge. Below are a few examples of how you can deal with bright and dark light situations.
Conditions with plenty of available light
Let us use an example of an aperture of f16, a shutter speed of 1/125s at ISO 100. This corresponds to an EV value of approximately EV 15 which is a normal bright sunny day.
If the light changes at gets brighter than EV 15 you will have to reduce the amount of light hitting the sensor. There are two ways you can do this in the camera:
- Using a faster shutter speed (> 1/125s)
- Stopping the lens down (> f16)
Both these adjustments are safe to do (no need for a tripod)
Bright light and long shutter speed
If you of creative reasons want to use a long shutter speed under the same light conditions as below, you are limited by the lens max aperture. Let say you want to blur the waves on a beach.
Depending on how fast the waves move you will probably need a shutter speed of 1/8s or longer.
By looking at the Exposure Triangle you will find:
- From 1/125s till 1/8s is 4-stops
- You will need to stop down the lens 4-stops to compensate
- Four stops from f16 is f64.
Most lenses have a max aperture of f22 so you will not be able to use 1/8s without overexposing your image. In this case, you have to use a Neutral Density filter in front of your lens.
Important: A shutter speed of 1/8s will require you to use a tripod to ensure sharp photos.
Conditions with limited available light
In the previous example with bright light (EV 15) the settings was aperture f16, shutter 1/125s at ISO 100.
Now let’s assume you want to shoot on a heavy overcast day (EV 12).
In this example if you keep the aperture at f16 you will need to compensate 3-stops, meaning a shutter speed of 1/15s. This is a slow shutter speed that requires you to use a tripod.
The alternative to getting away with this is to adjust the aperture instead. If you keep the shutter at 1/125s, you need to open up the aperture to f5,6. f5.6 will be available on most lenses, but you will have a shallow depth of field in this case.
If you don’t have a tripod and you need the aperture of f16, your option is to adjust the ISO instead. 3-stops from ISO 100 is ISO 800. Depending on your camera, it is a good chance you will start to see image noise at this ISO.
Again a tripod gives you flexibility, and you avoid using ISO the get a proper exposure. As the light fades a couple of stops more, there are no options doing this shoot without the tripod. You don’t want to increase the ISO to 3200 unless you have one of the best cameras for low light photography.
Summary
By understanding how the Exposure Triangle is constructed you will be able to make the adjustments you need for any given light situation.
Most important is to understand the relation between aperture and shutter speed. If you adjust one of them up or down to let in more or less light into the camera, you must adjust the other the same amount in the opposite direction to keep the exposure the same.
You should only increase the ISO when the light is so low no other options are possible.