Photography for Testers Part 3: The Exposure Triangle and ISO

Welcome to Part 3 of our series “Photography for Testers”. This week we begin a basic photography tutorial on the exposure triangle and using your camera’s light meter. This info isn’t specific to testers. It’s meant to help anyone who would like to learn more about using their camera in manual mode. We will go over what the exposure triangle is and what it’s three elements are. Also how each element affects your photo individually and then how to tie them all together to get the proper exposure. We will also discuss how your camera’s light meter works and the different types of metering available. This covers a lot of information, so it will be broken down into 5 separate posts. This week will be the exposure triangle and ISO. This will be followed with weekly posts on shutter speed, aperture, metering and then how to bring it all together.


The Exposure Triangle


By WClarke [CC BY-SA 4.0 (], from Wikimedia Commons


What is exposure? In photography, exposure is the amount of light that your camera’s sensor “sees”. It affects how light or dark your photo will be. Too much light means your photo is overexposed. Not enough light means it’s underexposed. The “correct” exposure is a balance of three things: ISO, shutter speed and aperture (also called an f-stop). These are often referred to as the three elements of the exposure triangle. These three elements work in relation to each other to make a photographic exposure. Because of this, when you change any one of the three, it affects the other two, making it impossible to isolate just one element.


If you think of the exposure triangle as a perfect triangle, will all sides and angles the same, it represents the correct exposure. If you change any of the three elements, the sides and angles are now unequal. This is no longer the correct exposure. Now you must change one, or both, of the other elements to make them equal again. We will come back to this after we go over the three elements individually.


(Above, I say “correct” because, for any given scene, there is more than one “correct” exposure. Which “correct” exposure you choose will depend on the look you are going for. Examples of this will be in the section on tying the three elements together.)




We’ll start with ISO, which I believe is the easiest element for people to grasp. ISO stands for International Standards Organization. It is a scale used for measuring the sensitivity of your camera’s image sensor to light. With digital cameras, you have a much broader range of ISOs than with traditional film. With traditional film, you were also limited to what film you had in your camera. Film was only available at 50, 64, 100, 200, 400, 800, 1600 and 3200. With digital, you can fine tune your ISO because you have the ability to choose speeds in between. The typical range for digital cameras is 100, 200, 250, 320, 400, 500, 640, 800, 1000, 1250, get the idea.



Now, what do these numbers actually mean? It’s fairly simple, really. The lower the ISO number, the less sensitive the sensor is to light. You would choose this when there is a lot of available light, like on a bright, sunny day. The higher the ISO number, the more sensitive to light it will be. You would choose a higher ISO when shooting in low light situations. Keep in mind, though, that higher ISOs can produce noise. This is similar to the grain of higher speed film and looks like tiny speckles throughout your photo. Noise can make your photos look less sharp than when using lower ISOs. Also note that some cameras perform better at higher ISOs than others.


You can see here how changing just the ISO affects the photo. Each increase lets in more light.


You can see the difference between ISOs here. See how the noise starts to show the higher the ISO. 


So, to break it down in the simplest terms:


High ISO = low light = more noise/grain

Low ISO = lots of light = no noise/grain


ISO is pretty straight forward, but I hope this was helpful and that you now have a better understanding of ISOs. As always, feel free to leave any questions you might have either here or on the PTP Facebook page. Next week will be all about shutter speeds. 

Thanks for reading!