The Hitech 85mm Orange No. 21 Resin Filter darkens blue, violet, green and yellow-green. It's particularly useful for all landscape and architectural photography (on black and white film) requiring vivid contours. The sky is distinctly toned with the clouds clearly contrasted against it. It is suitable for landscapes and nature scenes. This filter measures 85 x 85mm and fits the Cokin P series holder and the Hitech "P" series holder. The Filter factor is 4 (+2 stops).