We can use focus to guide the audience's attention and create depth in an otherwise 2-dimensional image.

automatic over-ride focus

Many cameras have a very helpful automatic over-ride button which will temporarily let the camera find the focus and lock it there when it is released back into manual mode.

If the camera is left on auto-focus it may annoy your audience as it randomly searches to focus first on the foreground then background. This often happens when someone walks across a shot

Difficult focus situations

  • Low light levels (such as night time): Where it can be difficult to see if the subject is sharp (and the wider aperture will give a narrower depth of field making focus more critical)
  • Low contrast: Flat light can be harder to find focus in than bright sharp sun light
  • Moving subject or camera: If either your subject or your camera is moving such as in a hand held scene, the plane of focus may be constantly changing making it more difficult to maintain focus

Keep it out of focus - I want to win the foreign picture award - Billy Wilder

Focus for HD

Focussing in High definition is more difficult because the tolerances of the higher resolution are lower; and what you might not see when filming could be very noticable when you finally view your work.

Depth of field

Simplified massively, depth of field is how much extra stays in focus in front of and behind what you have actually focused.

deep depth of field deep depth of field
shallow depth of field shallow depth of field

Deep Depth of field

Normally you want the biggest, deepest depth of field because:

  • It just makes things easier to keep everything in sharp focus.
  • There is more tolerance. ie. If a character, who has to walk into a shot, and deliver a difficult line, doesn't quite hit their intended mark they will still be in good enough focus - and you will have a usable take
  • With group shots more of the group stay in focus. It becomes possible to 'split the focus' between your performers. We could probably do with a picture demonstrating deep depth of field to contrast the narrow dof image. I've included 2 images here to demonstrate but I'm afraid I don't have clearance for use.

Shallow Depth of field

A very cinematic technique that makes everything in front of and behind your subject ‘soft’, isolating them in the frame and removing any distractions from the performance.

Controlling depth of field

Depth of field is a function of aperture (sometimes known as iris) in relation to image size (controlled by the lens's focal length, cameras chip size and how far away your charater is from the camera (subject distance).