GET TO GRIPS WITH DEPTH OF FIELD
Aperture provides the key to controlling depth of field and how much of your image is in focus
However fast your shutter speed, there’s no guarantee that everything in your picture will be sharp, because lenses can only precisely focus on one distance at a time. Fortunately, parts of the image at other distances don’t necessarily look out of focus – there’s always a range of distances that look acceptably sharp to the human eye. The range that appears in focus is known as the depth of field. This can stretch for miles (from your feet to the distant horizon), or be restricted to just a few millimetres. Three factors dictate how much depth of field you have to play with:
01 Focusing distance
The closer you are to a subject, the less depth of field you capture. This is why depth of field is so limited when you’re using a macro lens for close-ups, even at narrow apertures. It’s the distance at which you focus the lens that’s crucial, so it’s critical to choose where the lens is targeted.
02 Focal length
The wider your lens, the more depth of field you have to work with. Wide angle lenses produce images with adequate depth of field even at fairly wide apertures, while long lenses produce images with shallow depth of field, even at quite narrow apertures. This is why accurate focusing is so critical with long lenses – if your focus point is even slightly off, the part of the scene that you want to be sharp will be unfortunately soft.
03 Aperture
The narrower the aperture, the greater the depth of field. A wide (large) aperture of f/4 will mean that less of a scene is in focus than if you use a narrow (small) aperture of around f/11 to capture the whole scene in focus.