https://www.wildlifephotographyafrica.com/the-relationship-between-aperture-and-depth-of-field/
If you have an old lens, you could see depth of field on your lens:
This is an f2 lens.
The depth of field is expressed as between two same numbers, such as between left 4 and right 4. or between left 22 and right 22. The number above depth of field is the focus distance in meter or feet.
If you use f2.8, the depth of field is very small. If you use f22, the depth of field is very large.
