B+W Filters 46mm Yellow-Orange 040 Glass Screw In Filter for Black and White
Filters for black-and-white photography improve the differentiation of gray tones. On normal black-and-white films, colors that appear clearly distinct from one another to the human eye, for instance red and green, are reproduced nearly identically. Without appropriate filters, therefore, red blossoms with a green foliage background are rendered as flat black-and-white images without a distinct separation of the flowers from their background.
Black-and-white exposure filters block the light components of their complementary colors (i.e. the colors that are positioned across from each other on the color circle), rendering them in darker tones. Subject colors that are the same as the filter's own color, on the other hand, are reproduced in lighter tones. Thus a red filter will lighten red blossoms and simultaneously darken green foilage, whereas a green filter will produce exactly the opposite effect.
But in both cases the differentiation of the gray tones will result in a more brilliant photograph that corresponds more closely to the accustomed perception of the eye "in color". Some filter colors are available in different densities, which are designated light, medium or dark. The "light" density produces the mildest effect and "dark" the strongest.
Colors become gray shades
Black and white films should render all colors in shades of gray in such a way that their brightness values look natural. Older photographers can still remember that in earlier days yellow filters were a must for landscape photographs and for portraits. Even films that were sensitized "panchromatically", ostensibly to match human brightness perception, still rendered blues too lightly and reds too darkly. Even though today's black and white films no longer have that shortcoming, filters are still necessary for controlling the photographer's translation of colors into shades of gray.
Black and white photographs often lack impact because colors that are well differentiated in nature be equivalently luminous in shades of gray. For example, the red tiles on a roof and the green of nearby vegetation. But this can be managed: The color of the filter and its related colors are transmitted virtually undiminished, whereas their complementary colors are attenuated, so that they will appear darker in the photograph. When that loss of brightness is compensated in accordance with the filter factor, the result will be a correctly exposed picture that shows the color related to the color of the filter as lighter shades of gray. Complementary colors will appears darker tones.
Filters with TTL metering
Today nearly all SLR camera feature TTL (Through the Lens) exposure metering, which means through an attached filter as well. This metering method takes into account the loss of light absorbed by the filter, so that filter factors usually need not be applied. However, when the exposure is measured with a separate exposure meter, then the filter factor has to be taken into consideration. Still, with darker filters (very dense colors), exposure bracketing of ±1/2 to ±1 aperture stop is recommended, even with TTL exposure metering, because the spectral sensitivity of the metering cell can be significantly different from that of the film.
More differentiated greens
Why does the use of a yellow-green filter lead to a much better differentiation of green tones in nature and landscape photography? Here is the answer: Green can be a spectrally relatively pure green, but it can also be a blue-green & yellow-green mixture. Whereas pure green is readily transmitted by a yellow-green filter, an equally bright mixed-color green will have its blue-green component reduced, so that it will appear darker in a black and white print, darker than the gray tone generated by pure green.
Brightness vs. color contrast
Unlike color photographs, black and white photographs only have brightness contrast, no color contrast. That is why in the photography of objects, for example, things that have different colors but the same brightness will have similar gray values. For instance, when there is a blue toy in the foreground and red dress with the same brightness in the background, they will be reproduced with the same gray values. This is referred to as insufficient tonal separation.
Colored filters are helpful in such situations First the photographer must decide which object is to be rendered lighter and which one is to be rendered darker. Then he can select a filter color that 1) is similar to the color of the object that is to be shown lighter and that 2)is as complementary as possible to the object that is to be rendered darker. If the two colors are already nearly complementary, like blue and orange, he selects a filter color that is similar to that of the object that is to be rendered lighter. If the two main colors are not complementary, like blue and red, a compromise can be used: A blue filter lightens the blue color, but it also darkens the red color a little. But a green filter could also be used. While it would only lighten the related blue color a little, it would darken the red color more strongly than the blue filter world. The photographer would have achieved his objective in either case: a good tonal separation with the lighter gray of the toy and a darker gray for the dress.
B+W UV 010
Black and white films are also sensitive to the effects of invisible UV light. A high percentage of UV light, present in a clear view at the sea or mountains, results in a hazy and washed out picture. The UV 010 blocks out this light. Filter factor is 1.0.
B+W 021 light yellow 
This filter accentuates warm, soft, delicate scenes through the enhancement of yellow, orange, and red. It is especially suitable for portraits of women and children, skin tones in natural light, springtime landscapes, and nature scenes. Filter factor is approx. 1.5.
B+W 022 medium yellow 
This filter creates subtle differences between green tones and enhances the natural rendition of the sky. It is recommended for landscape and foliage photography. It tones down skin blemishes and ruddiness in daylight portraits, and results in soft skin tones as well as intensified blond hair. Filter factor is approx. 2.
B+W 023 dark yellow 
This filter distinctly improves reproductions of fine structures such as sand or snow, increases contrast of foliage, and clears distant haze. It diminishes skin blemishes and freckles in artificial light. It also darkens eye colors and lightens lip colors. Filter factor is approx. 3.
B+W 040 yellow-orange 
This bright-orange filter darkens blue and violet as well as green and yellow-green. It is indispensable for all landscape and architectural photography which require vivid and clear contours. The sky is distinctly toned with the clouds clearly contrasted against it. This filter is popular for nude photography under natural light. Filter factor is approx. 4.
B+W 041 red-orange 
This filter creates a strong darkening of the sky, dramatic storm-like cloud reproduction, and strongly enhanced shadows due to its enhanced contrast. It also achieves good tonal differentiations in still-life photography by brightening yellow, orange, and red. Filter factor is approx. 4.0.
B+W 060 yellow-green 
This filter is ideal for scenes where it is important to differentiate the green tonal values. The application is especially suited to landscape photography in the springtime because it enhances the light green color of the leaves. Due to its favorable effect on red tones, this filter is also suitable for portraits or group pictures taken in natural light. Filter factor is approx. 2.
B+W 061 green 
This dark green filter creates distinct differentiations of green tones in late spring and summer. It is also recommended for floral pictures that are used graphically, for tonal separations in still-life photography, and for the correction of red tones in portraits with high-speed film. Filter factor is approx. 3.0.
B+W light blue 080
This filter is recommended for the correction of artificial light with overtones of yellow-red such as with older photo lamps or normal household bulb illumination. It is also used to darken skin tones for portrait or nude photography under natural light. Filter factor is approx. 1.5.
B+W blue 081
The blue 081 enhances the tonal rendition of the sky by emphasizing mist in valleys and transmitting light rays over water, fog, and haze. In addition, this filter is used for the tonal separation in still-life photography and the correction of the light spectrum from artificial light sources. Filter factor is approx. 2.
B+W 090 light red 
This filter is ideal for enhancing contrast. In landscape and architectural photography, it enhances white areas, for example, letting clouds stand out clearly against a darkened sky and drastically reducing distant haze. It is also used for tonal separation in still-life photography. Filter factor is approx. 5.
B+W 091 red 
The use of this filter gives a surrealistic effect in landscape and architectural photography by producing a "storm-like" cloud effect, "moonlight" effect, and "wood" effect. It is indispensable for tonal separation in still-life photography and for the reproduction of documents which have become illegible. Filter factor is approx. 8.