Bruce Barnbaum - The Art of Photography - An Approach to Personal Expression

This photograph was made with a telephoto lens and two filters: a #12 deep yellow filter and a polarizing filter. With sunlight coming in through the hazy sky from the right, the polarizer helped separate the tonalities of the sky from those of the clouds by darkening the blue sky, which exhibits polarized light. It had little effect on the lower portions of the scene. The deep yellow filter further separated the tones of the sky and clouds without darkening the forested lower slopes. A #25 red filter would have created even greater cloud/sky separations but could have blacked out the trees. Thus the yellow filter was a better choice. Yet when I made the print, I dodged the forest throughout the basic exposure, then burned the top two-thirds considerably, then did an enormous amount of additional burning on the top third.

Figure 7-1. Mt. Samson and Peaks of the Canadian Rockies

Here we have two facts of great importance to start our discussion of filters:

White light is a combination of all colors.

Most objects radiate significant amounts of all colors of the spectrum.

It must also be mentioned that few digital photographers use filters, relying instead on software to do the work later in image manipulation, particularly for black-and-white work. Black-and-white filters can be used with digital cameras, but for numerous reasons it makes little sense to do so. The digital approach here is completely different, relying on the three color channels of the original capture to process the image—or even different parts of the image to different percentages of the three channels. This would be the rough equivalent of filtering each part of the image in isolation, without concern for any damage that filtration may cause to other parts of the image. This can prove to be a great advantage if done properly and subtly.

For color digital images, the channels can be manipulated to different percentages in various parts of the image to achieve an optimum color balance in each portion of the photograph. This can be done with one or more software packages that allow such manipulation. These digital approaches are worth learning fully, and applying sensibly, for the highest quality color image making.

Now let’s begin the discussion of filters, recognizing that the discussion applies primarily to film. Yet the thoughts behind these tools are valuable to learn, even for those shooting digital. Their application is universal.

Black-and-White Filters

All black-and-white photographic filters (yellow, orange, red, green, and blue) allow light waves to pass through that are the same color as the filter itself. Other colors are impeded to a greater or lesser extent depending on two things: the strength or depth of hue of the filter and the “oppositeness” of the color of the light wave from the filter. Thus, a red filter allows red light to pass through unimpeded, but it impedes yellow, green, blue, and other colors to varying degrees, depending on how close they lie to red on the color sphere (Figure 6-6).

In black-and-white, all colors are seen in terms of their gray equivalents on the axis of the color sphere. When two objects of different colors have the same gray tonal value, it may be difficult to separate them in black-and-white. The classic example of the red apple and green leaves comes to mind. There is no problem separating them in color, but in black-and-white they both translate to a middle gray tonality. Textural differences help separate them, but only through filters can their tonal values be changed to create a visual separation of the tones.

Let’s say you use a red filter during exposure of the red apple and green leaves. The predominant red rays of the apple pass through the filter, but the predominant green rays of the leaves are stopped. Because the green rays are stopped, they don’t reach the negative and the leaves appear darker on the final print. The leaves don’t become black, however, because other colors reflect off their surfaces, and those colors pass through the filter to sensitize the negative. Some of the colors reflected off the apple are stopped by the filter, but at a far smaller percentage than those radiating off the leaves. Thus, the apple appears lighter and the leaves darker. If a green filter were used, the opposite effect would occur: the apple would be darker and the leaves lighter.

Which filter would be most appropriate? This question brings us into the realm of interpretation and creativity. The green filter is the more “realistic” choice because the darkened apple appears heavier. Psychologically, we ascribe greater physical weight to dark objects. The green filter would be more in keeping with this fact, while the red filter would oppose it. Of course, there may be a good reason to purposely fight the natural, comfortable feeling. You may want to create a feeling of strangeness or a slight off balance. It’s a matter of individual preference and creativity.

When you understand what various filters do, you can use them as interpretive and expressive tools. This is crucial for creative photography. Full knowledge of your equipment is immaterial unless you use it to further your interpretive goals. And, of course, you cannot further your goals unless you first define them.

If two filters have the same color, the darker or deeper filter is the stronger one, and allows a smaller percentage of other colors to pass through it. Thus, a deep red filter allows little but red radiation to pass through and blocks a greater portion of other colors than a medium red filter. A yellow filter, which is lighter-hued than red, allows substantial amounts of colors other than yellow to pass through. For example, the #12 yellow (or “minus blue”) filter cuts out blue light almost completely. For this reason, the deeper-hued filters are considered stronger filters, as they have a more pronounced effect on the relative intensities of light passing through them.

All filters require an increase in exposure to compensate for the amount of light being stopped. Stronger filters require substantial increases in exposure. This exposure increase is known as the “filter factor”. A #25 red filter, for instance, requires a three-stop exposure increase over the unfiltered exposure because only of the light hitting the filter passes through it! Ignoring the filter factor can result in a disastrous underexposure.

Because the red filter prevents , or 87.5 percent, of the light that hits it from passing through (on average), it does not truly lighten reds within the scene as most people think. Rather, it darkens everything. But because you open up three stops, you compensate for the overall decrease in light. The red portion of the spectrum is not stopped by the filter, so red objects are selectively lightened in comparison to other objects. An object that is pure red (i.e., that emits only red rays of light) is not affected by the filter because its rays pass through unimpeded; but because you open up three stops to compensate for the filter, it is brightened by that amount. An object that is pure green (i.e., that emits only green rays of light) is totally stopped by the red filter and reads as black no matter how much you increase the exposure! The only reason that a green leaf appears at all is that it emits colors other than green that do pass through the filter to the negative.

Note

Full knowledge of your equipment is immaterial unless you use it to further your interpretive goals. And you cannot further your goals unless you first define them.