The Exposure Triangle Explained
Exposure triangle! Welcome to our 4th and final article where we discuss the exposure triangle and how we can alter each side of the triangle to make a photograph. Before we get started let’s do a quick recap.
The exposure triangle is made up of three components.
- ISO
- Aperture
- Shutter speed
Each one of these three components contributes to the final exposure.
ISO: ISO controls the sensitivity of the sensor to make it more or less light sensitive.
Aperture: Aperture controls the opening of the lens diaphragm. This opening is measured in F stops. The aperture of the lens is controlled by the diaphragm which is made up of blades which open and close to make the opening of the lens either larger or smaller thereby letting in more or less light.
Shutter speed: The shutter speed is the period of time that the shutter is opening exposing the sensor to the light. The longer the sensor is exposed to the light the brighter the image.
Now, let’s start by saying but there is no right or wrong way to use any one of these three parameters. There are many different conditions the governed the way that you use them. The two main ones are how much light is available in the scene and the artistic component of your photograph.
The easiest way to learn how to use ISO, aperture and shutter speed is by using the manual mode of your camera. This way, the camera will not make any automatic decisions on your behalf, and you will understand the effects of changing any one of those parameters.
So let’s now discuss how we can use these three components to craft an image in a particular scenario.
Scenario 1 – You are taking a portrait of a friend at the beach on a really bright day using a 50mm lens. Somewhat of a rule that I have is to always start with the ISO. I will set my ISO to 100 and I will come back and change it if I have to later on. Once I have my composition, I will want to decide on what the background should look like. When shooting portraits, I often blur the background. This really helps to make that person in the photograph stand out and can be really pleasing to the eye. So in this case I’m going to shoot the photograph at F 2.8. F 2.8 is a really wide aperture. This is going to give me a shallow depth of field which means but the background he’s going to be really out of focus and blurry. This is referred to as Bokeh. now that I’ve set my aperture and I’ve got my ISO set to 100 I will need to use the camera’s light meter to determine what my shutter speed should be. almost every light metre in all cameras work the same way. It will have a little diagram when you look through the viewfinder that shows you if your photograph is going to be exposed correctly. Typically it looks something like a ruler. See image below.
In the middle of this ruler there should be a value of 0 at either side of that zero there going to be some measurements. Typically these measurements go up to three that is, they’ll be the number 1, 2 and 3. on the other side of the zero they’ll be exactly the same thing only these ones will be negative numbers so that is -1, -2 and -3. your camera thinks that if you change the shutter speed to where the little indicator is on the 0, you will get what the camera thinks is a good exposure. Most of the time this is right, but not always. By changing the shutter speed so that it’s in one of the other numbers you can either overexpose or underexpose buy the correct amount. Those numbers that you see at either side of the O I referred to us light stops. You will also notice that there’s going to be either 3 or 4 little nudges between those numbers so that if you only wanted to modify your exposure by a smaller amount than one complete stop , you can then do so. For now, let’s just change the shutter speed and till the indicator is on the 0 (the middle of that ruler. If you now take the shot, there’s a very good chance that the photograph is correctly exposed. If the photograph is too bright, you can adjust the shutter speed and bring it down so that the indicator is at the -1. You’ve now set your camera to underexpose by 1 stop. If the photograph is too dark, just changed the shutter speed again so that it’s pointing to the number 1. If the photograph is still not bright enough change it again to number 2 and so on. Note that you can continue to change the shutter speed beyond the limitations of your Exposure display inside the viewfinder. That just isn’t enough room and most adjustments and made between zero and three stops.
Scenario 2 – You are taking a group shot of a football team. They are outdoors and there are 4 rows with 5 players in each row. Just like in scenario one, I’ll start off by setting my ISO to 100. The thinking behind this is that I want to get the best quality image possible. At ISO 100 I will have very little noise if any. Shooting of group of people presents an additional problem to solve compared to shooting just one person. Where is the depth of field when shooting one person can be quite small, we now need to make sure that the people in the first row and the people in the 4th row are all in focus. Knowing this I will change my aperture to F-11. F 11 is a fairly small aperture and it’s going to provide me with enough depth of field to make sure that every person in the photograph is in focus. However, by setting the lens to F-11, with close to down significantly and it’s going to be letting in a lot less light. Once we have the composition, we will look through the viewfinder to see our light metre. In this instance, the light metre says we should be shooting at 120th of a second. 120th of a second is a very slow speed, if we shoot at this speed there is a very real possibility that will get movement in the photograph causing it to be blurry. We cannot open up the lens anymore to a larger aperture because we then run the risk of not having everyone in focus in the photograph. This is what we have to go back to the ISO. In this instance we’re going to raise the ISO 2 ISO 800. Because the sensor is now more sensitive to light we can shoot at a much faster shutter speed such as 180th or one 100th of a second. This should be fast enough to be able to freeze any movement from the group.
As you can see from the two scenarios we’ve just discussed, the three components of the exposure triangle give you a great deal of control to be able to shape your photograph. The key to mastering them is practise. Shooting in manual mode when you’re first starting out can be very frustrating. You’ll have to think about every photograph before you take it and what those settings should be. Rest assured there will be a time well you will make all these decisions almost subconsciously. They will become second nature and you’ll know in a fraction of a second which setting you need to change to achieve the desired outcome. Once you master these, you may find that shooting in some of the other semi automatic modes such as aperture priority or shutter speed priority worked really well for you. But there will be a time where your camera just cannot get it right and this is where you could fall back to your knowledge and your level of comfort knowing that you can shoot in manual mode and override anything that the camera is trying to do for you so that you can get the exact photo you’re trying to get. So now it’s time to take that scary step. Put your camera in manual mode and go out and take some photos. Experiment. I guarantee you are going to fail more often than not in the beginning, but I can also tell you that you will get better at it, you get used to it and there will come a time when you’re not even thinking about it and just making the changes automatically in your head. Got any questions about the exposure triangle? Leave your comments or your questions below and I’ll do my best to help you.