The Tiffen 2 x 2" CC40R Red Filter is a color compensating (or color correction) filter for use when making color balance adjustments. It can be used to alter the color balance of a scene by placing in front of a light source or the lens of your camera. It can also be used to apply color corrections when used in the darkroom with an enlarger or to help pre-visualize color adjustments when viewing prints.
Red is the opposite of cyan and can be used to reduce cyan tones or casts within a scene or print. This red CC40 is more dense than a CC30 filter and less dense than a CC50 filter, and requires a 0.6 stop compensation for normal exposure results.
Tiffen filters are made using ColorCore technology; a process that involves laminating the filter substrate between 2 pieces of optical glass and grinding flat to a tolerance of 1/10,000th of an inch. This filter measures 2 x 2" / 50.8 x 50.8mm.