The Heliopan 40.5mm #11 Yellow-Green Filter is a basic contrast filter, primarily for use with black and white film, that moderately darkens blue and red tones, lightens green tones, and helps to subtly increase overall contrast. It also helps to better simulate a natural tonal response when working with panchromatic film under artificial lighting conditions. There is an approximate 2x filter factor with this filter, requiring an increase of 1 stop for normal exposure. The front and rear surfaces of the filter both feature a single anti-reflection coating. Each coating helps to increase light transmission by reducing reflections, scattered light, and ghosting. Additionally, they offer protection to the filter substrate while helping to keep the glass clean for longer than uncoated glass. This Heliopan filter is constructed from Schott glass for increased optical clarity and color fidelity. It features a brass filter ring for durability as well as jamming prevention.