This page does not relate directly to darkroom work, but I have had so many questions regarding filters for SLR cameras, that I have decided to include a section on them.

If you are using a single lenses reflex camera (SLR), then you can attach colored filters to the front of your lens. When used with black and white film, these filters can greatly enhance your photographs. These colored filters can be used in a variety of situations, such as minimizing haze in scenes or to increase the contrast of your images.

Since most filters absorb some light, your exposure must be adjusted when using them.

If you have an automatic SLR with through the lenses metering, simply screw the filter onto the front of the lens and take your picture. The loss of light coming in through the lens will be detected by the internal light meter and the camera will adjust its setting in order to get a correct exposure.
If your SLR is manual, or an automatic with a manual setting, first take a light meter reading through the lens and make a mental note of the reading. Screw your desired filter to the front of your lens and using the Filter factors listed below, either adjust the f-stop (most common method) or adjust the shutter speed, by the amount indicated.

To make an object appear darker on film than it does to the eye, select a filter that has a color which is complementary to the color of the object. For example, a yellow, orange or red filter will darken a blue sky. If you use filters of complementary colors, you can make objects in your picture stand out from each other, rather than all being potentially the same shade of grey.

A dark red filter on a bright day with a partly cloudy sky, will very much enhance and define the clouds. An orange filter will do the same to a lesser degree and yellow to an even lesser degree.

A yellowish green filter is very good for portraiture in soft sunlight or with multicolored flowers (remember - we are still talking about black and white photography).

Filter factors: - Aperture Adjustment.

• Factor of 2 (Yellow Filter) open aperture by 1 f-stop - (example - from f16 to f11)

• Factor of 4 (Orange Filter) open aperture by 2 f-stops - (example - from f16 to f8)

• Factor of 8 (Red Filter) open aperture by 3 f-stops - (example - from f16 to f5.6)