d. Red (Wratten no. 25, also called A or R1).
Red filters are very
They darken blue skies dramatically, making them almost black in
many cases, with white clouds standing out brilliantly against them. They
also add brilliance to sunset scenes, penetrate haze, and enhance textures
even more effectively than the deep yellow. An even deeper red, called no.
29, can make a blue sky almost black, and its other effects are equally
This filter is so strong that it is chosen only for special
situations, and is not used as often as the no. 25. The choice between no.
15, no. 25, and no. 29 is mainly one of deciding how dramatic you want your
results to be in the finished picture.
Filter recommendations for black-and-white