Spectrum of some common photographic filters

This page shows the spectral response of a few photographic filters that are usually mounted on top of SLR lenses.

UV filter

The UV filter is most often usually used for mechanical protection of the lenses and not really for it's optical characteristics. It's originally intended for removing the UV light, that is not visible by the human eye, that could fool the exposure control of the camera or saturate the film.
Ideally it should be completely transparent to the visible light and stop the UV radiation. The measured filter (a "HOYA HMC 52mm UV(0)") looks clear (not colored) indicating that the response is good. The measure shows a cut-off wavelength of 390 nm and an almost flat response in the visible part of the spectrum (let's say between 450 and 700 nm).

Raw measures of this filter between 350 nm and 2500 nm is available here.

Skylight filter

The skylight filter is similar to the UV filter discussed above and is generally used for lens protection, but instead of having a flat spectral response it slightly attenuates blue. This is useful to reduce the blue color of the sky that is usually reflected almost everywhere in the landscape.
The filter (a "HOYA HMC 58mm SKYLIGHT(18)") appears slightly pinkish, meaning that red light is less attenuated than blue light. This is also visible in the measured spectrum. On that spectrum one can also see that this is a bad UV filter since UV light (wavelengths shorter than 400 nm) are not very much attenuated. The cut-off wavelength seems to be around 350 nm, which is typical for normal glass.

Raw measures of this filter between 350 nm and 2500 nm is available here.

80B filter

The 80B filter, as all filters in the 80 series, is used to rise the color temperature. This particular filter will make the yellowish light produced by tungsten lamps appear white on daylight optimized films. The 80B filter is designed to increase the color temperature from 3400 K to 5500 K.
This filter (a "HOYA HMC 58mm 80B") appears blue because of it's attenuation of red light and, since tungsten lamps produce maximum radiation in the red region, this will make the overall spectrum more uniform and the light will look whiter. Of course this will reduce the overall amount of light available for the picture and the exposure time or the aperture usually need to be increased by 1-1/3.

Raw measures of this filter between 350 nm and 2500 nm is available here.

81B filter

The 81B filter, as all filters in the 81 series, is used to decrease the color temperature. The 81B filter is designed to decrease it from 3500  to 3200 .
This filter (a "HOYA HMC 58mm 81B") appears orange because of it's attenuation of blue light. Of course this will reduce the overall amount of light available for the picture and the exposure time or the aperture usually need to be increased by 1/3.
The measure below shows that this filter is also a good UV filter since radiation of shorter wavelength that 404 nm is cut off.

Raw measures of this filter between 350 nm and 2500 nm is available here.

Circular polarized filter

Circular polarizing filters are used for their ability of removing reflections that are usually composed of partially polarized light.
Measuring the spectrum of such a filter will not produce any information about polarization; it will only tell if the filter is neutral or attenuates any particular color.
This filter (a "HOYA 58mm PL-CIR") has a very good neutral (flat) response in the visible spectrum (between 400 and 700 nm). On the other hand losses in the filter are very important, but this is normal in polarizers.

Raw measures of this filter between 350 nm and 2500 nm is available here.