What are the three variables that affect depth of field?

The three variables that affect depth of field are subject-to-camera distance, aperture, and the focal length of the lens. If you want a shallow depth of field to get a good bokeh effect, a telephoto lens at a distance with a low f-stop is the best combination. If you want a wider depth of field, a wide-angle lens with a high f-stop at a distance from the subject will result in almost everything in sharp focus.

The goal of your answer is to showcase an in-depth knowledge of the technical aspects of photography.

Focus on the three variables and the effects of depth of field. Show the interviewer that you have a good command of the factors involved with the depth of field by explaining how to get different effects through the use of depth of field.