A visual language of photography
Today’s cameras, including your smartphone, take pretty good photos automatically – just press the shutter button. But reliably getting GREAT photos still takes a human to point the camera and to know how to control it. And at the heart of camera control is ‘exposure’ – how light is record as an image.
Understanding exposure is a photography super-power. It’s what sets professionals apart and, while this knowledge is rare, the first steps are easy to learn – read on.
What is ‘Exposure’?
The process of making a photo is fundamentally the same for every camera, from a vintage wooden pinhole, to an SLR to the latest and greatest multi-lens smartphone.
It starts with one essential ingredient, light, and then a three-step process inside the camera to record that light as a photo.
- light enters the camera through an aperture (hole),
- it’s allowed in for an amount of time and
- lands on a surface that is sensitive to light
Together these four add up to the brightness of your final image. And like links in a chain, you need them all. If there’s no light, no aperture, no time, or no sensitivity, you’ve broken the chain and there’ll be… no photo.
The Exposure Triangle
First let’s look at the conventional way of learning about exposure. The exposure triangle is one of the first things you find when you start learning about photography and exposure. It shows shutter speed, aperture and ISO and provides labels for happens when you increase or decrease these.
The ‘exposure triangle might sound like a good place to start. But on closer inspection its usefulness is limited. Lets see what its useful for and then clarify what it can’t do.
What is the exposure triangle useful for?
- The Exposure Triangle is a visual mnemonic; a way to remember there are three camera controls for exposure.
- It’s also a visual hook on which to hang further knowledge about the side effects of those controls (motion blur, noise, depth of field).
What are the limitations of the exposure triangle?
- 1. It can’t tell you how bright your photo will be – in other words it can’t calculate an exposure.
- 2. You can’t visualise the exposure values of a photo.
- 3. You can’t use it to control a camera
Enter Exposure donut
There is one thing we can add to the triangle that links ISO, shutter speed and aperture into a nice formula. The missing ingredient is light!
We get the exposure donut which becomes a lot more useful.
- It can tell you how bright your photo will be
- It can visualise the exposure values of any photo,
- It can use it to control a camera
Light + aperture + time + sensitivity = photo brightness
This is the exposure donut, or ‘expodo’ for short. Its four coloured arcs visualise how Light, aperture, time, and sensitivity add up to the brightness of your photo.
DONUT CONTROLS BRIGHTNESS
The Exposure Donut controls BRIGHTNESS: You can have more of one arc (e.g. stronger light), and less of another (e.g. a smaller aperture to let less light in) but they will always add up to the brightness of your photo. And when the coloured arcs add up to a complete circle your photo has a normal brightness, as shown in the middle of these three images.
But normal, often called ‘correct exposure’ won’t always be what you want. The photo on the right is the stand out shot of the three and it was achieved by making the photo darker than normal. This is visualised by an incomplete exposure donut. If we’d wanted a brighter-than-normal image, like the one on the left, then we’d need a more-than-complete exposure donut.
Keep in mind all three images were all taken seconds apart. And you can see that the yellow arc is the same length in all three shots, telling us that the strength of the light was the same length in shot. We changed the length of the red and blue arcs (time and sensitivity) to change brightness in these images.
Here are another three images, this time showing how over or under exposing might give you a more interesting photo.
DONUT CONTROLS SHARPNESS
Exposure isn’t only about brightness. It also controls how sharp (or blurry) your image is.
The Exposure Donut controls SHARPNESS. Understanding the exposure donut gives you the ability to control trade-offs between the brightness and sharpness of your photo. Sharpness, or its opposite blur, actually comes in three flavours; background-blur, motion-blur, and grain-blur.
Increasing the red arc adds time for motion (in your scene or the camera) to appear in the image. The arc moves on a logarithmic scale. This means that a small change has a large effect.
These two images were taken moments apart, the first with a 1/15th second exposure, the second with a 1 second exposure. By having the lens open for that much longer, the sensor looked at the scene 15 times as long and the spark trails are 15 times longer.
Taking photos in low light with your camera or smartphone in AUTO often results in noisy/grainy images – like the photo on the left. There’s not enough light information coming into the camera to create a sharp bright image. So the sensitivity of the camera has been increased to turn what would have been a dark noisy shot into a bright but noisy one. The only way to get a sharper image, like the one on the right, is to let more light in. This is done by increasing the red arc (the blue arc is reduced so the photo doesn’t become too bright.
Rather than brightening the image by amplifying a small (and noisy) image signal, the longer red arc adds more time for light to come in. light is information, so more light makes for sharper images. Note that if there’s movement in your scene (or your camera) you’ll also be adding motion blur by increasing the red arc to make the blue shorter.