The Heliopan 28mm Medium Yellow Filter is a basic contrast filter, primarily for use with black and white film, that slightly darkens skies, helps to cut through haze, and improves overall contrast. It is the most common contrast filter for black and white photography, producing an accurate tonal range and compensating for the blue sensitivity of panchromatic film. Increases the visible grey tones of green objects such as foliage. There is a 2.5-3x filter factor with this filter, requiring an increase of 1.3 to 1.5 stops for normal exposure.