3) Camera Distance

The third way to change depth-of-field is to change the distance between the camera and the subject.

Getting close to the subject means LESS depth-of-field. Moving away, means MORE depth-of-field.

Shooting a scene with a car (20 feet away) and a building (100 feet away) and a mountain (5 miles away) means that will ALL be in focus, because nothing is very close.

Conversely, shooting a scene with a billiard ball (8 inches away) and a pool player (3 feet away) and the back wall (8 feet away) means that it will be tough to get all three in focus at the same time. Again, because the camera is  close to your subjects,  depth of field is limited.