In memory of John Westley

B&W film converts all colours, pale & saturated, sunlit or in shade into shades of grey. Modern films do this very well, but the interpretation does not coincide with the rendition of these colours made by our eyes. Perhaps the most apparent example of this is film's interpretation of sky and clouds, where our eyes 'see' a bright blue sky as being much darker than white clouds.

Modern films are much better than their earlier counterparts, which were more sensitive to blue than other colours, and as a result could not differentiate between blue and white (seen mainly as 'blue' by early films.) Relative colour response improved greatly with the development'Panchromatic' films which became more readily available in the 1940s. Kodak's Super XX was an early entry, with a speed of IS0125 ... really fast for those days. Nowadays, all films except graphic copying films are panchromatic.

As B&W films are sensitive to all wavelengths of visible light (with the exception of very deep green), what are the benefits of using 'on camera' filters?

An understanding of the colour wheel and complementary colours is a big help in choosing the correct filter for the job. Cyan (blue green) may be thought of as 'minus red'. Yellow may be thought of as 'minus blue'. Magenta may be thought of as 'minus green'. All colours have their complement, or 'minus' equivalent.

The result of this is that a yellow filter extracts any blue from the light reaching the film, so that a blue area on the negative will be less dense than it would have been without the yellow filter. In the print, a blue area will appear darker than otherwise. On the other hand, any yellow areas within the image area will appear darker on the negative and hence lighter in tone on the print than it would have been without a filter. Likewise, a red filter darkens blues and greens and lightens red colours, and a green filter darkens orange red and violent but lightens green colours. A filter of any colour lightens its own colour in the print, but darkens the filter's complementary colour.

Notwithstanding this apparent simplicity, the effects of different filters can sometimes be difficult to predict. It is a good idea to' bracket' your filter selection if you are uncertain.

Red filter
A red filter will greatly darken the blue sky, and dramatise any clouds within it. It will darken green foliage, and generally increase the overall contrast of the negative.

Yellow filter
The yellow filter darkens blues sky to a lesser extent than a red filter, but still gives a pleasant emphasis to any clouds in the sky. It will also emphasize texture when photographing snow, as the shadow areas creating the texture are generally more blue, being lit by more blue light from the sky. Exposure must be increased by 2 stops.

Orange filter
An orange filter, I colour resulting from the mixture of red and yellow, can affect the film to an extent in between yellow and red, so darkens blue sky and foliage in a more gentle way than a red filter. Increase exposure by 1 to 1.5 stops.

Yellow — green filter
The yellow green filter darkens skies to a somewhat greater extent than the yellow filter, but at the same time lightens any greens which at present. It is a very useful filter, and many photographers leave one on the lens all time. Exposure increase 1 stop.

Green filter
A green filter is not commonly used, but maybe useful if you need to lighten the green colours in a landscape. As programmatic films are less sensitive to green than any other colour, exposure may need to be increased by 2 —3 stops. The green filter all so darkens a blue sky moderately and emphasizes clouds.

Blue filter
A blue filter is not normally used in landscape or general photography, as it tends to reduce the film's relative sensitivity to differentiate between blue and white. However, it maybe useful and giving a better title representation to skin tones and textures and portraiture work.

Polarizing filter.
Polarizing filters are normally used with colour film, but they can provide some very useful affects when used with black and white film. They darken blue skies dramatically at some angles and elevations of the sun. Generally speaking maximum effect is seen when photographing at right angles to the direction of the sunshine. Be careful when using one with a wide-angle lens, because the angle of view may be great enough to encompass a range of polarizing affects, resulting in a wide variation of tone in the blue sky.

The filter is always very useful on dull days because of its ability to reduce/remove reflections from nonmetallic services. Firstly, the effect is to increase contrast at a time when lighting conditions are very dull and flat. The filter can remove -- partly or fully, reflections on water. The water becomes more "transparent" to rocks etc beneath the surface of the water.

Exposure must be increased by 2 stops to counteract the neutral density affects of the polarizing filter.

Polarizer + red filter
You can combine the polarizer and a red filter to get extreme affects from clouds in a blue sky. The combination of these two filters can give a completely black sky under the right conditions. However, you will lose 5 stops and tripod will almost ertainly be necessary to avoid camera shake. Even with a tripod any breeze may cause movement of your subject and result in blur and lack of sharpness.

John Westley April 2005