There are 2 basic types of filters which
are recommend for anyone considering rig shots on a
regular basis. They are Polarising filters, usually slim versions if
available, and a range of Neutral Density (ND) filters ranging from
about 3 to about 10 stops. Stacking a Polarising filter with an ND will
also allow some fine tuning if needed. If shooting only indoors then there
is little if any need for filters at all.
Polarising filters are very
useful for rig shots, and for general car photography. Polarising
filters are normally used to control reflections in panels or on glass,
or to darken the sky or reflections on other surfaces in the background.
Polarising filters usually reduce light by about 1.5-1.75 stops so they
can be used in conjunction with ND's to reduce light intensity and allow
a longer exposure. The exposure compensation of ND and Polarising
filters are simply added so for example, using a 3 stop ND filter with a
polarising filter will require an exposure compensation of approx 4.5
Neutral Density (ND) filters reduce the amount of light which passes through them so they are often used for rig shots because of the long exposures often required. Neutral Density filters are meant to pass all visible wavelengths of light equally so that they don't create a colour cast but in practice most ND filters don't quite do what they are supposed to and colour casts of varying degrees are common, especially with stronger filters. ND filters don't always filter infra red as well as they do visible light so this excess of infra red can lead to a colour cast in cameras with greater infra red sensitivity. Some cameras are simply more sensitive to infra red light than others, hence a stronger colour cast. Colour casts are not always easy to correct and are some times impossible to eliminate altogether.
When selecting filters it's usually best to buy the thinnest filters you can, usually called 'slim' filters, so that you can minimise the chance of vignetting with wide angle lenses. Always check if the filter you are buying has a front thread as filters which don't have a front thread will prevent you stacking another filter on top. It's also a good idea to buy the largest filter that you might need, usually 77mm or 82mm for Canon and Nikon, and then use step up rings if the filters need to be used on lenses which require a smaller filter. Filters are expensive, step up rings are very cheap.
The table below is an example of the kind of choice you might find in ND filters. This table shows the filters available in a 77mm thread from B+W, Heliopan and Hoya in 2009 and is not meant to accurately represent B+W, Heliopan or Hoya's products. See each manufacturers web sites for accurate and up to date product information. Other filters may be available in other thread sizes.
Aperture and Shutter speed combinations with filters
The above table shows the range of
exposures possible in full sun with a range of exposure compensation
values. For example, a 9 stop ND filter will allow a 4 second exposure
at F16, at ISO 100 in full sun. Other combinations can easily be
estimated using the above table.