This is a good example of how a No. 12 yellow filter can accentuate a sky and bring out cloud detail. Using this highway in New Mexico as a tool to enhance perspective leads the eye into the picture and gives a great feeling of space. Shot with a Canon EOS 1DS, 28mm lens, 1/125 sec, f/11.

The most useful filters for black-and-white landscapes are yellow, orange, red, green and one or two graduated ND (neutral density) ones of different strengths. A No. 12 yellow filter is essential for enhancing the sky, making a blue sky slightly darker and adding definition to clouds. Most filters, except UV and skylight, require an increase in exposure. As the camera’s TTL (through the lens) metering should adjust for this, there is no need to override the exposure, but it is worth checking the histogram to make sure the levels are evenly spread across the graph.

An orange filter produces the same effect but more so, darkening the sky even further, while a No. 25 red filter can make a blue sky so dark that it looks as though it were photographed at night. A No. 25 requires an increase in exposure of about 1 stop but, again, the TTL metering should adjust for this. Although this filter can add a sense of surrealism to your shots, it can also make them look unevenly balanced and tacky.

Filters the same colour as your subject will lighten it. For example, a green filter will turn a mass of green foliage lighter, whereas an orange filter will darken it. Lightening foliage in black-and-white photography can be beneficial because it often appears quite dense and heavy when reproduced at printing stage.

If you use a coloured filter and are shooting colour as well as black-and-white, remember to remove the filter each time you switch mode, otherwise you will have a colour cast on all your colour shots.

John Freeman is a highly experienced professional photographer and author of several books on photography, including Practical Photography, Lighting for Interiors, and Photographer: The Complete Guide to Taking Photographs. He has a regular column in What Digital Camera? and Digital Camera magazines. For further information and a gallery of his photographers, visit www.johnfreeman-photographer.com. His book is available from Watson-Guptill Publications as well as other retailers.