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 (\(f\))
- the f-number of the lens opening (\(N\)), i.e. the aperture
- the camera-to-subject distance (\(s\)), i.e. the object distance in optics terminology

The DOF formula is expressed as:

\[\mathrm{DOF} \approx \frac{2 N c f^2 s^2}{f^4 - N^2 c^2 s^2}\]where $c$ is the diameter of the circle of confusion, which is 0.018mm for APS-C and 0.029mm for 35mm film.