Factors affecting Depth of Field
3. The Aperture
The aperture is an opening within the lens whose size is controlled by a series of overlapping blades. It’s sole purpose is to control the amount of light that reaches the film or sensor during the exposure time.
Fig. 5 demonstrates how depth of field changes through aperture only. The camera/subject distance and the lens focal length are fixed. Only the aperture was the changing parameter.
At f/2.8, the lens is at its widest aperture. The lower the value, the wider the aperture.
Light travels through the lens via its wide aperture thus creating a shallow depth of field.
On the contrary, at f/22, (smallest aperture), depth of field is at its highest as light rays propagate through the narrower lens opening, squeezing out the DOF and makes it longer.
Conclusion:
The wider the aperture (f/2.8), the shallower the depth of field.
The smaller the aperture (f/22), the longer the depth of field.