Depth of Field is dependent upon two main factors: (i) the size of
the aperture (ii) the position of your zoom control (i.e. focal length).
You will have maximum depth of field when the aperture is small and
the zoom is at the wide angle end. And vice-versa.
Pulled Focus
If you want to try a 'pull focus' shot (i.e. moving the focus from
one object to another) then you need to reduce the depth of field
which means opening the aperture. This in turn will cause your picture
to overexpose, so the best way round this is to fit a NEUTRAL DENSITY
FILTER which reduces the amount of light coming into the camera. You
could also try increasing the shutter speed but take care with moving
subjects as this might cause jerky movement (but it's fine for a portrait
type shot). Then move your camera back a fair way such that you need
to zoom up fully to fill the frame with your subject (remember that
on full zoom you WILL need a tripod). So now you have maximum aperture
and full zoom, providing you with the MINIMUM depth of field. Using
manual control, focus on the foreground object (e.g. a flower) shoot
that for about five seconds then gradually move the focus ring away
from the camera (anticlockwise) until the background object come into
focus. VOILA!* You've just done a pull focus shot. Practise this and
you'll soon become proficient and start looking for other creative
ways to use this effect.
