Yellow #12 Screw-In Filter
The #12 Yellow Filter from Tiffen is a filter designed to increase contrast and tonal separation for black and white photography. The filter absorbs blue colors, rendering blues darker. Haze is minimized for aerial photography and excessive blue is removed for astrophotography. The #12 Yellow Filter is recommended as a basic filter for use with Kodak's Aero Ektachrome Infrared Film. The filter has a filter factor of 2, so you must increase by 1 full stop to your exposure to compensate.
Tiffen filters are not dyed, but are manufactured by using ColorCore technology. This process laminates the filter material between two pieces of optical glass and grinds down and polishes the glass. The glass is then mounted to the metal ring, which after that can be screwed onto the lens for the desired effect.