The Hitech Black & White Filters are used to reduce or eliminate atmospheric haze, make the tonal reproduction in monochrome imagery more natural and give deliberate emphasis to certain tones and objects. Filters for use with black and white film have strong colors that block wavelengths sufficiently enough to produce shifts in grey tones.
The Yellow 8 greatly increases contrast and is particularly useful for midday sun and deep shadow. It accentuates clouds, reduces haze and will reproduce distance better. The Yellow/Green 11 retains tonal value but reduces haze and brightens green. The Red 25 and Orange 21 accentuates red picture parts set off against green or blue, e.g.. it will make clouds brighter against the sky.