The depth of field (DoF) is simply the area of an image that will be focused relative to your position. This area which varies from a few centimeters to several metres and is directly influenced by the size of the sensor, the aperture, the length of your focal length and the focusing distance. A low depth of field means that only your subject will be sharp, whilst a great depth of field will mean that the whole image will be in focus.
Rather than provide complex mathematical formulas, we will instead try to provide you with the main rules in order to obtain either a shallow depth of field or an immense depth of field.
Why want to play on the depth of field?
The question sounds stupid, but why don’t you just want everything to be right? First of all, artistic intent. Both photography and cinema which demonstrated this most effectively in detaching an actor or a subject from their background. The image is aesthetic because the attention is focused on the action and not elsewhere, which will be blurred with a bokeh effect. On the other hand, a camera operator covering a breaking news story for example would ensure that everything is clear and won’t necessarily have time to correct the point by running behind a subject. When using a gimbal on the other hand, we rely upon a camera’s autofocus or we switch to hyperfocal to be sure of the point since our hands are of course tied up.
The rules: sensor size, aperture, focal length, focusing distance:
- 1. The size of the sensor: this influences the depth of field, but not as much as we think: with identical focal length, aperture and framing, it will be necessary to”get closer to the subject” when working with a large sensor to obtain the same framing as with a small sensor, which will have an effect on the blur of background produced. The closer a subject is to the objective, the shallower the depth of field. So it’s the necessary distance that influences the depth of field.
- 2. The aperture is the main parameter for controlling the depth of field. It’s very simple. The more open (f/2.0 for example), the smaller the depth of field. On the other hand, the closer you close, the cleaner you get. The amount of light can be controlled by playing on the neutral filters. (see our article on the exhibition).
- 3. The focal length: here again, the data is important. With a 24mm (Full Frame) wide angle, everything will tend to be very sharp (even with a large opening). You’ll have to get a lot closer to your subject to make the background blur. On the contrary, with an 85mm (telephoto lenses) and beyond, the area of focus is naturally very reduced and it will be necessary to close much more to make the background clear.
- 4. The focusing distance: you will have understood it with previous notions i.e. the farther a subject is, the closer it is to the background and closer to the hyperfocal zone. In other words, everything will be clean. The closer it is, and even with a small sensor, the more blurred the background will be.
The focus zone follows a golden rule. If you make the point on a subject and the depth of field (net area) is 3 meters, you can consider that everything will be clear: 1 meter in front of the subject and 2 meters behind him: it is the rule of 1/3 – 2/3.
To go further and try different settings, we recommend you take a look at https://dofsimulator.net/en/