ABSTRACT
Photographic filters are transparent plates that are designed to modify the properties of light before it reaches the film or sensor of a camera. Filters usually are mounted in front of the camera lens, though some large lenses permit rear mounting. The filters of interest here fall in the following categories: neutral density (ND) filters that attenuate light at all wavelengths; color filters that modify the spectral distribution of the transmitted light by attenuating the intensity at certain wavelengths; and polarization filters that transmit light polarized in a certain direction. This chapter discusses these filters primarily in terms of their usefulness for digital photography. In digital photography one must deal with CCD or CMOS sensors in place of film. These sensors are inherently sensitive in the red/IR region, so much so that without blocking ambient IR the recorded colors may be distorted, i.e. IR will be will falsely recorded as a visible color.
