essential skills: digital photography in available light
Filtration
The purpose of a fi lter is to selectively modify the light used for exposure. Filters are regularly used
by professional photographers. They are an indispensable means of controlling the variations in
light the photographer is likely to encounter. The range of fi lters used varies according to the range
of situations likely to be encountered. However, when capturing RAW fi le images it is possible to
undertake color correction in post production.
UV fi lters
Ultraviolet (UV) radiation present in the spectrum of light is invisible to human vision but adds
to the overall exposure of the image. It is most noticeable with landscape images taken at high
altitude and seascapes. To ensure the problem is eliminated, UV fi lters can be attached to all
lenses used on location. If the optical quality of the fi lter is good the fi lters may be left permanently
attached to the lenses. The added benefi t of this practice is the front lens element of each lens will
be protected from scratching.
Neutral density fi lters
With manufacturers going to great lengths to create fast lenses with wide maximum apertures it
may seem strange to fi nd a range of fi lters available which reduce the amount of light at any given
aperture. These are neutral density fi lters and are available in a range of densities. If only one is
purchased the photographer should consider one that can reduce the light by at least two stops
(four times less light). Neutral density fi lters are used for two reasons:
~ Reducing depth of fi eld
~ Increasing duration of exposure.
Mark Galer