The Tiffen 4 x 4" #6 Yellow 1 Filter is a basic contrast filter, primarily for use with black and white film. This 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 partially compensating for the blue sensitivity of panchromatic film.
There is a 1.2x filter factor with this filter, requiring an increase of about 0.3 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 ten-thousandth of an inch. It measures 4 x 4" / 101.6 x 101.6mm.