Some Useful Filters for Black and White Photography
(See pages 92-93 in Barbara London’s "Photography".

Yellow #8, has a filter factor of 2 (You need to increase exposure by 1 stop) - General purpose landscape filter. Darkens a blue sky realistically, brings out clouds. Increases contrast a bit by darkening bluish shadows. Reduces bluish haze.

Yellow #15, has a filter factor of 2.5 (You need to increase exposure by 1 1/3 stops) - Lightens yellow and red subjects. Darkens blue water and sky, Reduces bluish haze and brings out clouds more than a yellow #8. Increases contrast in landscapes.

Green #11, has a filter factor of 4 (You need to increase exposure by 2 stops) - Enhances foliage. Darkens sky somewhat. Darkens red and brown values such as brick, rock and soil.

Red #25, has a filter factor of 8 (You need to increase exposure by 3 stops) - Dramatically darkens sky. Increases contrast in a scene by darkening shadows. Shadows in a scene are mostly produced by light reflected from a blue sky and will appear very dark with a red filter.

Polarizing, Can be used to remove unwanted reflection from nonmetallic surfaces, such as water and glass. Requires 1 to 1 1/3 stops additional exposure. Darkens the sky and reduces haze. Absorbs light waves traveling in certain planes relative to the filter. A polarizing filter is most effective at reducing reflections at about a 35 degree angle to a reflective surface (such as glass or water). To reduce haze in the sky a polarizing filter is most effective when you are taking pictures at approximately 90 degrees (a right angle) to the position of the sun. . (Can also be used with color film to reduce glare and darken the blue of the sky).

Neutral density (or ND) - Absorbs light equally from all parts of the spectrum. Increases required exposure so camera can be set to a wider aperture or slower shutter speed. (This can be helpful when you need a slower shutter speed to blur motion, or a wider aperture to decrease depth of field). comes in varying densities. (Can also be used with color film as it will not change the color balance).

1A (Skylight) - Absorbs ultraviolet. Little or no effect on black and white scenes. Often used to protect the lens surface from damage.

UV (Ultraviolet) - Same as 1A above. I very highly recommend that you keep either a 1A or UV filter on all of your lenses at all times. If scratched they are much less expensive to replace than a lens.

On Buying Filters: When buying a filter you will need to know the diameter of your lens. Look at the engraving on the ring on the front of your lens. Some lenses show the diameter in mm, following a circle with a line through it. If you don’t know bring your lens with you to the camera store. If you are using an autofocus camera you will probably need a "circular" polarizer. If you are using a manual focus camera you will need a "linear" polorizer.

Using more than one filter: If you use 2 or more filters at the same time simply add up the number of stops you need to add (or multiply the filter factors together to determine the correct number of stops you need to add). You may experience some vignetting (darkening around the edges of your image) when you stack up filters. (You may like this effect).