What I’m aiming for is the article I wish I’d found when I first got my camera, to help explain the relationship between three critically important parameters: the ISO speed, aperture (or f-stop number), and shutter speed.
To lead with, the easiest way I think to approach these three things is to understand physically what they mean inside your camera. So, here we go.
- ISO speed: A measurement of how quickly your camera’s sensor absorbs light.
- Shutter speed: A measurement of how long your camera’s shutter is open for when you take a shot.
- Aperture: A measurement of how wide the shutter on your camera’s lens opens up when you take a shot.
For completeness I should note that ISO speed is not specific to digital cameras with sensors. On film cameras, a particular roll of film will have a specific ISO speed that it is rated for. Fortunately for DSLR users like us, we can change the ISO speed without having to change film. All three of these parameters affect how light gets to your camera’s sensor to create an image, so let’s start looking at them in more detail.
