DEPTH OF FIELD - (DoF)

For most of us attempting to grasp the workings of their camera for the first time, this trio of esoteric sounding names seems confusing.

The three aspects to what is termed, the Exposure Triangle are; Depth-of-Field, Shutter Speed and ISO. DoF is the first of these. The ‘Field’ is the area that is viewed through your viewfinder, the area between your camera lens and the amount of viewed frame that you wish to capture. The ‘Depth’ is the area of this field that you wish to be in focus. If you look at a distant landscape, your eye can see from your position to the horizon, in focus, in its entirety. Your camera lens on the other hand, cannot. It only focuses on one part of the scene at a time. You need to set it to record what YOU want.

The following images show the field that has been captured, plus the depth, set by the aperture.

Soft background. The lens aperture here is f.2, and only the nearest branches are in focus. Small f number = SMALL DOF.

Clearer background. We have closed the aperture or ‘squinted’ it to f.22 so more of the foliage is now in focus. Large f number = LARGE DOF.

Soft background, sharp foreground

Soft foreground, sharp background

Sharp foreground, clearer background

f5.6 @ 5000th second

f36 @ 250th second

Aperture wide open, focus on foreground

Aperture wide open, focus on background

Aperture closed to maximise depth of field

Aperture wide open, focus on foreground

Aperture wide open, focus on background

Aperture closed to maximise depth of field

Aperture wide open, focus on background

Aperture wide open, focus on pigeon

Aperture closed to maximise depth of field

a) f.4 - 2000th second. Fence in focus

b) f.32 - 30th second. Aperture closed to increase depth of field

c) f.4 - 2000th second. Farm in focus

Your lens focuses on one part of the field at a time - about the width of your hand - not all of it. You increase or decrease this depth with your aperture. The smaller the number, the smaller the field of focus will be, the larger the number, the more of your field will be in focus, as in the snow covered twigs above. When you are first starting out it can be confusing to hear people talking about opening or closing your aperture, or using different f stops. Although it all refers to the same thing, it helps to simplify your approach. So if you get stuck, just remember:

Large f number = large dof. Small number - small dof.

Small number, small DoF

Large number, large DoF

This close up shot of the bride has a small dof of f.2.8, hence the blurred makeup artist in the background and foreground mirror. So you can see that the ‘field’ is only about 20cms in depth. If more of the field was in focus it may well have spoilt the moment, anyway it would be a different image.

A different approach was used for the couple, where greater depth-of-field of f.11 was needed so that most of the scene was in focus.

The opposite applies when shooting interiors where a large depth- of-field is needed. Here the entire field is in focus, so a tripod was essential for a shot like this. Large number, large DoF (f.32). Because of the large aperture number, it meant less light was entering the camera therefore a 2 second exposure was needed. The ultra wide 12mm lens meant that I had to correct the vertical lines to stop the fish bowl effect.

All photography and information © Jon Davison 2022.

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