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This scene has a wide range of tonal values. The deep blue sky, the bright white clouds, the sign and the church siding all reflect varying degrees of light. Finding the right exposure for such a scene is a challenge.

Heading up to the Kancamagus Highway in the fall, you anticipate taking the world’s greatest foliage pictures. The sky is blue, the sun is shining brightly and you’re thinking “What a beautiful day.” You spend the afternoon, mid-afternoon at that, taking pictures and you return home confident you have nailed it. Back come the pictures from the lab and the trees are half in bright sunlight and half in dark shade. There is little color to speak of, based on what you thought you saw, and the sky is a bland blast of white. What happened? Tonal values happened, that’s what!

All objects have tonal values that measure their relative luminance (or reflected light) to other objects in a scene. A bright sky has more luminance (higher tonal value, more reflected light) then a dark black rock. The difference in the tonal values of objects in a scene is a measure of its contrast. Determining the tonal value of the darkest and brightest parts of a scene yields its contrast range. Depending on that range, a photograph may not register detail in all objects in the scene.

The human eye is an amazing organ. The pupil dilates (opens) when confronted with darkness and constricts (closes) in brightness. The aperture of a camera mimics the eye. The major difference is that the eye can adjust to differences in light instantaneously. When you take a photograph, you must set the aperture, and shutter, at single values. Translating a scene in the world to the film plane is an enormous problem that must be solved in order to make great images.

Understand and being able to measure contrast allows photographers to properly map the range of contrast in a scene to the relatively restricted tonal range of film or digital sensor.

For the church scene in Stark, NH pictured here, the meter says, “Wow! That building is bright; I better limit the exposure so the siding looks like a middle tone.” The picture comes back with grey walls, grey clouds and the whole scene looks dark. It is the cameras job to take the bright luminance of the clouds and the dark luminance of the sky and turn the whole scene into a drab, grey mess.

Properly measuring the contrast in the scene, the photographer discovers that the clouds reflect a good deal more light then the mountains in the background. Does the photograph record visible detail in the brightest white of the church siding and the darkest dark of the mountain?

There are a number of issues to discuss in order to completely understand this concept of tonal values and exposure. And, my friends, they don’t come easy.

For now, here’s a simple assignment to help you visualize contrast. Head out on a sunny, bright day. Pick a typical scene and point your camera around the scene, be sure to include dark areas, shadows, and bright areas. Record the meter readings for up to 5 different areas in the scene. Do they differ in tonal value? By how much? Are you able to determine the range of contrast in the scene? Will all areas in the scene show sufficient detail? If so, great, if not, what do you do?