Compared to the human eye, the camera’s vision has many shortcomings (as photographers are quick to lament). At the top of photographers’ list is the very narrow gap separating the brightest and darkest tones a camera can capture: dynamic range.
But while the camera taketh away, it also giveth. Experienced photographers understand that what we perceive as complete darkness is really just our eyes’ relatively limited ability to gather light, combined with the brain’s insistence on processing this limited input instantaneously. But a camera’s sensor (or a rectangle of unexposed film) can accumulate all the light striking it for whatever duration we prescribe, thereby stretching its “instant” of perception indefinitely. Advantage camera.
For example, the camera’s narrow dynamic range is (exquisitely) mitigated in the barely perceptible light preceding sunrise and following sunset. Unlike night photography, when the light in the sky is so faint that extremely long exposures are required to register any foreground detail, and daylight/moonlight photography, when unidirectional light casts high contrast shadows that exceed a camera’s dynamic range, pre-sunrise/post-sunset twilight light is spread so evenly overhead that most shadows disappear.
About this image
Horizon-to-horizon skylight made dynamic range a non-factor in the above Alabama Hills pre-sunrise scene, while my camera’s instant-stretching ability revealed beauty present in a landscape that was nearly invisible to my eyes.
White with snow and towering 10,000 vertical feet above the Alabama Hills, Mt. Whitney loomed in dramatic contrast to the dark sky and foreground. As my eyes adjusted to the limited light, the jumbled rocks of the Alabama Hills became vague, colorless shapes. Anyone relying on their eyes on this January morning would likely conclude that there’s not enough light for photography. But I knew better.
Juxtaposing a nearby fortress of boulders against Whitney’s serrated outline, I framed my image. While the mountains were the dominant feature to my eyes, I knew my long exposure would make the nearby rocks equally prominent—their sharpness was essential. Limited light made autofocus on the rocks out of the question, so I stopped down to f16 to increase my margin for error and focused manually.
As planned, a thirty-second exposure at ISO 400 uncovered volumes of invisible detail and color my eyes missed. (The scene took two or three exposures to get right as I really felt like I was composing blind.) Though I was photographing in a fairly stiff (and frigid!) breeze at 4,500 feet, it was nothing like the hurricane wind that smeared the clouds above Whitney to an ethereal glaze during the 30 second exposure. Another revelation of the long exposure was the sky’s exquisite, natural (not processing-enhanced) blue.
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