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Photograph Black cat by Richard Keeling on 500px

Black cat by Richard Keeling on 500px

You might think, after a lifetime of photography including at least ten years increasingly seriously devoted to digital, that I might know something about color.

I don’t.

Let’s qualify that. I don’t know nearly enough.

Parodoxically, it has taken my return to film photography, mostly black and white, to expand my knowledge.

Black and white pictures render color as a shade of gray. Obvious enough. But as that shade is now depend wholly on intensity of light, colors that reflect the same amount lead to similar amounts of shading on film. Whether they be blue, green, yellow or red – or any other color.

This makes it for difficulties in trying to distinguish different colors in black and white images. So how does one overcome this limitation?

By the use of color filters to alter the relative intensity of light striking the film emulsion. A color filter typically allows maximum transmission – brightness – of its native color, the one you see with your eye when you look at the glass. And they block or inhibit transmission of light of other wavelengths or colors. This usually occurs one one of two ways.

The first is an absolute gate, in the sense that light below a certain wavelength is blocked while light above that wavelength is transmitted. A yellow K2 filter, for example, blocks all light below a wavelength of about 470 nm while allowing longer wavelengths through. 470nm corresponds to blue, so using a yellow K2 filter darkens anything reflecting blue, such as the sky, while allowing greens, yellows, oranges and red through. This has a net effect of lightening these colors, with the greatest lightening apparent for yellows.

The Orange K, and Red 25A filter work in similar ways, only at differing wavelengths. As orange is longer than yellow and red longer than orange, the filtering effect on the visible spectrum becomes more pronounced, progressively removing not only blues, but preventing greens and yellows too from adding light intensity to your image. Thus blues darken further, as do greens and yellows. The effect is to boost contrast and add drama as the effective color palette range is trimmed.

Other color filters work in slightly different ways. The Hoya K0 yellow-green and K1 green filters are peak transmitting filters. They allow yellow-green or green to pass but inhibit light of both shorter and longer wavelengths, with the blockage absolute before yellow into blue and partial for orange-red and beyond into red. Thus yellow-greens and greens become intensified while all other colors are reduced.

The photograph above was taken using a K0 yellow-green filter. The cat is black, refecting little light of any color, but the vegetation is a blend of yellows and greens. Using this filter allows maximal transmission of those yellows and greens, producing a uniformingly consistent intensity and resulting in a bright but low contrast foreground and background.

It’s an unnatural look, but it does serve to cast the cat in sharp relief. Apart, that is, from the green pollen collecting on its coat.

So this black and white image has taught me a lot about color. Even though none is actually reproduced.

It’s discoveries and insights such as these that propel my continuing interest in photography. To be sure, I can read about it in books, but there is no substitute, as far as I am concerned, to actually doing it.

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