Understanding exposure in photography can be quite confusing and there are endless tutorials and articles written to help. Exposure is critical to capturing perfect photos as in a nutshell exposure equates to how light or dark your photo is. Good exposure will show a photo with whites that are not too dark or too bright and blacks that are not too black but not to light. On a histogram good exposure can look a little like this.
There are 3 elements to obtaining the right exposure – ISO, Aperture and Shutter Speed.
In the most basic terms:
ISO = how sensitive your camera is to light
Aperture = the size of the hole that lets light into your camera
Shutter Speed = the speed in which the hole is open to let light into your camera.
Have you ever had a bad migraine? Or suffered from a hang over? When you are out in bright light you are very aware and very sensitive of the light. Wouldn’t it have been nice to be able to adjust the brightness of the light or adjust how sensitive you were to how bright it was? Your camera can and this is ISO. When light is really bright you can reduce your ISO to a smaller number such as 100 or 200.
When you are in an environment where there is limited light you need your camera to take on as much light as possible so you want to make it MORE sensitive to the small amount of light available. Here you increase your ISO up to 1,000 or so.
I am going to go back to our migraine or hang over analogy. You are out in bright light and obviously quite sensitive to it. Your body’s natural reaction is the squint your eyes to reduce the amount of light that gets in. This is basically what you are doing to your camera, manually. When there is a lot of light your lens opening does not need to be as large to allow the light in so we reduce the size of the aperture e.g. f1/2. In a dark space you increase the lens opening to get as much light in as possible. Starting to make sense?
Back to our migraine or hang over. You step outside and into the light and you realise it is bright so your body reacts by quickly shutting your eyes to avoid the bright light hurting you. The speed in which you open and close your eyes in camera terms is shutter speed. The time in which the lens is open letting light in. On the flip side in darker spaces you are not so sensitive so can keep your eyes open and for a camera the longer the shutter speed the more light gets in.
All of these things work together to achieve the right exposure.
Let’s look at the exposure triangle as this helps to show the interaction of all three together.