This 6 x 4" Light Red #23A Filter from Formatt is used in black and white photography to suppress blue and greatly brighten red. This filter is commonly used in architectural photography to increase the contrast of building lines and enhance structural design. It also produces contrast effects that darken sky and water, as in more dramatic scenic photography.
Not as strong as a #25 but clouds are dramatically improved; Darkens blue sky creating dramatic contrast between sky and clouds
It is more effective in cutting through haze, and moonlight effects are easily accomplished; Creates greater contrast between foliage and flowers