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However, digital images (like film before them) can’t always stretch this far. If the brightness range (sometimes called tonal or dynamic range) of a scene is too great, the most a camera can do is aim somewhere in the middle.

Again, we’ll go into more detail on this later on. The key point now is that this is another way in which what the eye sees can be different from what the camera records. And understanding that fact is the start of being able to deal with it.

Aperture and shutter speed

Some cameras now have more exposure modes than you can shake a trekking pole at: Landscape mode, Portrait mode, Night portrait mode, Party mode, Alpine bivouac mode (OK, we made that last one up)… And yet the most important task that all of these modes perform is to determine how the camera sets aperture and shutter speed. You might never set these manually but they are still key to every shot.

Aperture just means ‘opening’. There has to be an opening to admit light into the camera, to reach the sensor (or film) which captures the image. Varying the size of that opening is one of two ways in which we control the amount of light admitted.