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Graphical display of aperture on screen of a Nikon D3100 (Jon)

However, varying the aperture also affects depth of field. This is a bad thing if it gives us results we didn’t expect, but it becomes a very good thing when we can exploit it to get more control over our results.

Trowbarrow Quarry, Lancashire (Jon) There are deep shadows behind this brightly lit white tree and the dynamic range is very high. However, the shot simply would not work if detail was lost in the tree bark

Raindrop (Jon) Sometimes the camera can freeze movement the eye can’t follow (shutter speed 1/250 sec)

Aperture, as we’ve already indicated, plays a key role in determining depth of field. The combination of these two controls determines the total amount of light that gets through to the digital sensor.

Aperture dictates how wide the lens opening will be: shutter speed determines how long it stays open.

Shutter speed is principally important in determining how movement is captured in the photo. And movement, naturally, is another major way in which what you see can be very different from what you get. This is inevitable in a still picture! The eye sees movement, but the picture is a still.