To make a deeper DOF, we can use:

  • Longer focal length
  • Wider aperture
  • Stay closer to the focus

Actually, the depth-of-field is determined by the three factors:

  • the focal length of the lens ()
  • the f-number of the lens opening (), i.e. the aperture
  • the camera-to-subject distance (), i.e. the object distance in optics terminology

The DOF formula is expressed as:

where $c$ is the diameter of the circle of confusion, which is 0.018mm for APS-C and 0.029mm for 35mm film.