neutral density filter Printable version

A gray filter that reduces all wavelengths of colors equally, achieving the effect of dimming the light source without changing its color temperature.

One manufacturer's offerings, from http://www.tlsinc.com/toolfilterfax.html:

Neutral Density Filters
Neutral Density filters are designed to reduce the intensity of light without affecting color temperature. They are usually applied to windows to reduce the level of exterior light and bring it within the range of interior light level.

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All four gel manufacturers, Rosco, LEE, GAM, and Apollo offer various intensities. http://www.leefilters.com/lighting/technical-list.html#&filter=control

Lee # - Desc - F-stop - Transmission - Roscolux - ApolloGel
Lee 298 - 0.15ND - reduces light 1/2 stop - 70% transmission - Roscolux 397 - no equivalent
Lee 209 - 0.3ND - reduces light 1 stop - 50% transmission - Roscolux 97 - Apollo 2310
Lee 210 - 0.6ND - reduces light 2 stops - 25% transmission - Roscolux 98 - Apollo 2320
Lee 211 - 0.9ND - reduces light 3 stops - 13% transmission - Roscolux 97 - Apollo 2330
Lee 299 - 1.2ND - reduces light 4 stops - 6% transmission - no equivalent - no equivalent