Technical Information from The Photographers Centre

Colour Filters for Black and White Film
You can alter the way black and white film renders a scene by placing a colour filter on your camera lens. A black and white print is a collection of grey tones, you can increase the contrast between these tones by using filters. A filter of one colour lightens subjects of the same colour and will darken other colours. All filters have a factor number which tells you the amount of extra exposure needed to compensate for the lost of light through the filter. Cameras with Through The Lens metering will usually compensate for filters and no additional exposure will be required. Filter factors are not always the same on even on filters of the same colour: factors listed below should be treated as a guide only.

Filter Factor Exposure Effect

Yellow x2 +1 stop Darkens blue skies moderately.

Yellow/Green x4 +2 stops Lightens foliage to separate it from blooms

Green x6 +2 ¹/₂ stops Lightens foliage.

Orange x4 +2 stops Darkens skies considerably, reduces freckles in portraits.

Red x8 +3 stops Renders blue skies almost black and increase contrast.

Skylight x1 none Absorbs ultraviolet rays.

Ultra-violet x1 none Clear Filter. Absorbs ultraviolet radiation. Used to protect lens.

NDx4 x4 +2 stops ND filters reduce only the amount of light.

NDx8 x8 +3 stops ND filters reduce only the amount of light.

NDx4 reduces amount of light to a quarter and NDx8 to one eighth.

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