The 81 Series of filters control the bluish coloration that affects daylight film. The 81EF is the strongest of the 81 Series filters. It is used for a maximum warming effect on very cloudy days or to more than eliminate (i.e. warm) the bluishness of open shade on a clear day. It can also be used to add a very "suntanned look" in portrait photography or add extreme warmth to sunrise or sunset photography.
This filter measures 130 X 170mm and only fits the Cokin X-PRO series holder.