The Tiffen 4 x 6" #9 (3) Yellow Filter is a basic contrast filter, primarily for use with black and white film. This medium yellow filter slightly darkens skies, helps to cut through haze, and improves overall contrast. It is a common contrast filter for black and white photography, producing an accurate tonal range and compensating for the blue sensitivity of panchromatic film.
There is a 2x filter factor with this filter, requiring an increase of 1 stop for normal exposure. 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 10,000th of an inch. This filter measures 4 x 6" / 101.6 x 152.4mm.