Category: Exposure

Exposure Compensation

Exposure Compensation is an absolutely critical feature of the camera to understand.

Exposure Compensation is a way to brighten or darken the image being taken without adjusting any of the properties manually.

You are taking the camera’s measurments (light-metering) and saying “okay, that, but brighter” or “sure, that, but darker”.

The exposure compensation icon is universal. It looks like this:


Exposure Compensation Icon by Martin Chapman Fromm from the Noun Project

Exposure compensation doesn’t do anything in manual mode because we aren’t using the camera’s settings. This is why the exposure compensation button is also – while in manual mode – what often serves to toggle which setting your dial adjusts – shutter speed or aperture, in manual mode.

More Reading on Exposure Compensation

Videos on Exposure Compensation

Learning Exposure

Learning path for understanding camera exposure.

Okay, so you understand The Parts of The Camera and What A Camera Does down? Time to talk about exposure!

Here is a path to follow in order to learn camera exposure.

1. Exposure Essentials
2. Exposure and Cameras
2. Shooting Modes
2. Exposure Compensation
2. Shutter Effects
2. Histogram

Have fun!

Exposure Essentials

Images are made with light captured from the world. We can consider (or “model”) light in many ways – as particles, waves, and so on. For photographers it’s most convenient to consider light as rays that travel in straight lines and bounce off of things. Simple enough.

Some rays may travel weakly, and some with great intensity. Consider this for brighter light sources and weaker ones. Light also gets weaker in brightness as it travels from a nearby light source.

As rays of light “travel”, a ray of light hitting an object for an instant and one that hits an object for a long time have different effects.

We need to absorb rays of light in order to capture an image. Lets consider the difficulty of focusing this light later, right now, think that if we don’t get enough light, we won’t be able to capture our image.

Remember those old glow-in-the-dark toys? They were greenish?

For one of these to be bright, they had to absorb enough light. If you didn’t leave the lights in the room on for long enough, they wouldn’t be able to glow; or they would glow very differently.

Picture an array of these stars, very densely packed together. If we shine a flashlight on them, but hold up shadow puppets in front of our light, then turn the light off, we will be left with an image – of sorts – of the shadow puppet. That’s…sort of… photography. Kinda. Making images by capturing light. Sure.

Film is made up of a shoot full of tiny little grains. A dense grid of them. These grains – similar to the phosphorescent stars – were sensitive to light. After we shined light at them, we then – through entirely different chemical processes than that with the phosphorescent rocks involving silver halide – we can “develop” the film, which makes the image that projected onto it permanent, no longer sensitive to light.

Then bunch of other things happen that we don’t need to talk about now, and we have an image.

In digital photography, we have image sensors made up of a bunch of little light sensors, each representing a pixel of an image.

In order for these little light sensors to show an image, we need to shoot enough rays of light at them, for a long enough period of time.

If we give them no light, it will be black. Like when you forget to take the lens cap off.

If you give it a lot of light, it will turn white.

Somewhere in-between, if we give it not too little, and not too much light, we can create an image that is grey. And one that is light grey. And one that is dark grey.

Get enough of these little light sensors reading various shades of grey, and you have an image! Images come out of contrasting elements. Dark next to light, and so on. Just like drawing. Blue ink can’t draw well blue paper. White pixels don’t show details next to other white pixels.

If they all were the same brightness of grey… we wouldn’t have an image. We wouldn’t if they were all black or if they were all white either.

Don’t worry. I’ve left my lens cap on enough times to thouroughly test the hypothethis that an all black image makes a good picture. It doesn’t. No need to test that yourself.

The key to getting an image to appear is that the bright parts of our image are not too bright (ie: not solid white), and the dark parts of the image are not too dark (ie: solid black).

Camera’s have a limited range of brightnesses that that they can capture. The range a camera can capture from the darkest point in the scene being just-barely black to the brightest point in the scene that can be not-quite-white is called the dynamic range. Nicer (usually newer, more expensive) cameras have larger dynamic ranges.

If we can capture our grey, detailed, image. Then that image can actually represent the world we pointed the camera at. We can do photography!

A major part of photography is adjusting three settings on the camera – the shutter speed, the aperture, and the ISO, which determine how much light gets into the camera.

The major technical goal of photography is to create an appropriate exposure. One that shows the scene with as much detail as possible: Not all black, not all white.

Exposure And Cameras

Make sure you understand your exposure essentials before reading this article.

Camera’s control how much light gets in by adjusting one of three things.

  • How LONG the camera lets light in for.
  • How MUCH the camera lets light in at a time.
  • How SENSITIVE the camera is to light.

Shutter Speed, measured in seconds, is how long we let light into. One second? One Thousandth of a second? Less time, less light, and \(all else equal\) the darker the image. I know “speed” is a weird way to talk about “time” but, let it go. Just don’t worry about it. If it really bothers you, then be like Canon and call it “time value” if you want.

Aperture, measured with in “f-stops” \(whatever that means\), is an adjustable hole in the camera. This hole can get bigger or smaller. Basically, it lets the _lens_ get bigger – and let in more light, or smaller, and let in less light. These numbers often have a decimal in them. Like “5 point 6” or “2 point 8”, or just “8”.

ISO, measured in… nothing, it’s just ISO. ISO stands for “International Standards Organization”, the people who decided what numbers to use so that all camera and film manufacturers would agree. Thank’s ISO! It refers to how sensitive the camera is to light.

We call this relationship the Exposure Triangle

Getting The Exposure Correct

Let’s say you’re at a soda machine. You want to fill up your cup with the perfect amount of soda, right to the rim. Too much and it overflows and your hands get all sticky. Too little and you’re left thirsty and dissapointed.

The shutter speed would be how long you hold the cup against the lever, how much time we let the soda out of the machine.

The aperture would be the nozzle. Think about the difference between getting a soda vs. the little water lever. The water trickles out, or comes rushing out.

The ISO would be the size of the cup. How much soda do we need anyway? How much before we are overflowing? Overflowing for a small dixie cup isn’t overflowing for a KFC chicken bucket!

How these different settings work with each other and how they affect your image – we’ll come back to that. Let’s learn how to mess with these settings on our fancy cameras!

To change these settings in action, see he section on shooting modes.

Videos on Exposure

*editors note: wow lots of really long-winded video explanations of the exposure triangle exist. Sorry. Watch a few of these things, and absorb the information. It’s not that difficult.*

These animations are decent.