Neutral Density filters are important tools for controlling light reduction. They
permit less depth of field under bright lighting since the aperture has to be
larger and, in addition, they permit long time exposures with stronger ND filters
in sunlight.
With digital imaging over exposure can be avoided resulting in natural color
reproduction. ND gray filters are manufactured from color neutral Schott
glass so they can be used for color imaging. They are available in 3 densities.
Higher densities are available on special order for technical and scientific
applications.
On most digicams the imaging sensor is smaller than the 35mm format. This
results in a relatively large depth of field, even with a large aperture opening
this can be disturbing - when eg. A portrait has to be separated from the bakkground
and the available light requires the use of a smaller aperture, reducing
the available light allows the choice of the best aperture. Also with digicams
that only operate in full auto mode, the depth of field can be reduced.
Digicams frequently have fewer apertures then film cameras, (eg. 2.8 to 5.6
or 2.0 to 8.0) a neutral density filter allows a much larger choice of exposure
combinations.