The 3 x 3" #21 Orange Filter from Lee Filters is a filter designed to build contrast in black and white photography and creates separation between the tones. The filter absorbs blue and blue-green colors, rendering blues darker such as for skies in landscape or aerial photos and water shots. The filter also lightens red tones, such as in Skin tones. The filter has a filter factor of 2, so you must increase your exposure by 1 stop to compensate.
The filters are manufactured from tough, polyester-based material which is easy to clean. Polyester filters can be mounted in filter frames to fit the Gel Snap or Foundation Kit.