EV, or Exposure Value, is a numerical measurement of the amount of light in a scene. We all tend to think of exposure in terms of shutter speeds and apertures, but in fact it’s the exposure value that it all starts from.

When you use a handheld light meter, it quotes an EV number which you then translate into shutter speed and aperture combinations using a rotating dial. When the camera measures the light level, it too starts with an EV number, which it then uses to decide shutter speeds and/or apertures, depending on the mode you’re working in.

If you want to use manual exposure control, or take more control over what shutter speeds and apertures the camera uses, a basic knowledge of exposure values is really useful. That’s why we’ve created a special download-and-print photo-facts guide, which you can download here.

You can use this guide to find out what possible combinations of aperture and shutter speed are available for a given exposure, or even to estimate exposures manually without a light meter at all.

The main thing to note is that the EV values quoted are for shooting at ISO 100. At higher ISOs, the light in the scene is, effectively brighter, and the easiest way to allow for this is to add 1EV to the value for each extra ’stop’ in ISO. So for shooting at ISO 200, add 1 to the value, for ISO 200 add 2 and so on. You only need to do this if you’re using the guide for manual exposure estimates. If you’re using the camera meter and just checking the table for different aperture/shutter speed combinations, you don’t need to do anything, since the camera has already allowed for the higher ISO.