15 March, 2016 by Simon Descoteau
Getting Started with Photography: Part 3 – The Exposure Triangle
Before we go too much into the purchasing of equipment, let us take a few moments to actually understand what is involved in taking a photo. Now strictly speaking I should have written this before I wrote the part on purchasing a camera, so I am going to retrospectively put this in as part 3, and update that to part 4. Shh, don’t tell anyone ;). I am going to only briefly explain what the 3 parts of the exposure triangle are so that you have a better understanding of what it is all about.
The exposure triangle consists of the aperture, the shutter speed, and the ISO. The target here is to balance these 3 elements in different ways to make sure enough light gets to the sensor or film to have a well exposed picture. If there is not the right amount of light, you can adjust any of the 3 in the triangle to achieve the desired level of light, but the one you choose will have an impact on the final image.
The way I was taught it, and is often explained is the “Bucket” analogy. Imagine you have a bucket, and you are filling it. When the bucket is full your image is correctly exposed. The size of the bucket is the ISO. The higher the ISO, the smaller the bucket and subsequently the less water you need to fill it. The size of the tap is the aperture. If the tap is big it will flow more water, just like if the aperture is large it lets more light in. How long the tap is open is is the shutter speed. The less time you have the tap open the faster the shutter speed. By balancing the bucket size, how large the tap is, and how long you keep the tap open, you fill up the bucket. In the same way, you adjust the shutter speed, the aperture and the ISO to perfectly expose the photo.
The shutter speed is how long the shutter stays open. It is measured in fractions of a second so when you see 500 what it is really saying is 1/500 of a second so the bigger the number, the shorter the amount of time the shutter is open for. And a shutter speed of 250 will let in twice as much light as a shutter speed of 500 because the shutter is open for twice as long. A faster shutter speed will allow you to freeze action as the shutter is open for less time, where as a slower shutter speed may lead to blur either due to camera shake or the subject moving. It is advised that shutter speed is no less than the focal length of the lens. So if you are taking a picture at 200mm, avoid going slower than 1/200 in your shutter speed. A fast shutter speed is useful if you want to stop the action when shooting wildlife or sports where as a slow shutter speed can be used to emphasis motion such as water going down a waterfall.
The aperture is simply how large the hole is that the light is going through. It is a ratio of the diameter of the hole, and the focal length. Imagine a lens that has a diameter of 40mm and a focal length of 80mm, the aperture of the lens will be F/2 because 80/40 = 2. The larger the number, the smaller the hole is. So an aperture of F/4 would let in half the light that an F/2 lens would. The other thing to keep in mind is that the aperture has a part in dictating the depth of field, or how much of the image is in focus. The smaller the number, the larger the aperture, the shallower the focus area is. A large aperture is useful for occasions where there is not much light or when one is trying to isolate the subject in a portrait, where as a small shutter speed can be useful for getting a lot of things in acceptable focus, such as when taking a landscape photograph.
The ISO is how sensitive each pixel on the digital sensor, or each grain on a film is. By being more sensitive, you need less light in order to fully expose the photograph. However, by being more sensitive, you lose out on colour, contrast and sharpness due to the fact that when the sensitivity is turned up, there is also more noise. Generally speaking you want to try to use as low an ISO as possible to get the best image quality, especially with older digital cameras, but don’t be scared to push the limits. A noisy photograph is better than no photograph. There have been great advances in ISO technology but I wouldn’t worry about it too much at this stage. The ISO is dictated by a number. Most cameras have a native low ISO of 100, which tends to be the lowest and the one you should try to use as much as possible, assuming there is enough light of course. An ISO of 200 would be twice as sensitive as an ISO of 100. ISO 400 would be twice as sensitive again and so forth.
Hopefully this will give you some understanding on what the exposure triangle is, and you can start to play with the aspects of the triangle to understand how different settings change the look and feel of the final image. The best thing you can do is just have a play and see what happened. You’ll soon see what works and what doesn’t. As you will most likely have a digital camera you won’t have to worry about film development costs and can just look at the pictures on your computer right away. I look forward to hearing your experiences and thoughts, please feel free to comment or ask questions and I’ll try my best to answer them!