Yellow #8 (8 Yellow 2) is commonly used for a noticeable increase in contrast with black and white films.
Deep Yellow #15 is commonly used for a noticeable increase in contrast with black and white films. It is also used to increase the separation of clouds and sky in black and white photography.
Yellow 12 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.
Orange 16 is designed to build contrast in black and white photography. The effect of the contrast will be greater than the #15 yellow when shooting B&W landscape, marine, or aerial photos. Therefore, making skies more dramatic and darker.
Orange 21 is a filter designed to build contrast in black and white photography and creates separation between the tones. The filter absorbs blue and blue-green colors, rendering blues darker such as for skies in landscape or aerial photos and water in marine shots.
The #11 Green (1) Filter is designed to build contrast in black and white photography. When using this filter for portraiture in the outdoors it will lighten skin tones and have better separation between the subject and the background. Shooting landscape photos will help darken skies and lighten and show more detail in the foliage