One of the most important things to learn as you’re growing as a photographer is that your camera doesn’t “see” the way your eyes do. This principle manifests itself in a number of forms, but from a technical standpoint the two most important are depth of field and dynamic range.
Depth of Field
For our purposes, depth of field refers to the nearest and furthest points in a scene that appear acceptably sharp. Assuming unimpaired vision, when we view a scene with the naked eye, everything, from front to back, appears “acceptably sharp.” Depending on our camera’s optics and the aperture setting in use, this isn’t necessarily the case when we look through our camera’s viewfinder. How much of a scene we choose to render sharp is an aesthetic choice we make as photographers. The selection of optics and aperture are the accessible tools to make our choice a reality. But the greater point is, it’s possible to render scenes in a photograph in a way that mimics how we see it with the naked eye or in a manner that departs significantly from that naked eye view. By understanding how these optical choices display a scene, an entirely new world of creativity is thrown open to us.
You may have read or heard the terms “selective focus” or “shallow depth of field.” They refer, in effect, to a photographic effect that we can’t see with the naked eye. There are times when limiting sharp focus to certain areas of a composition can be very effective. Having only a small portion of an image in sharp relief can assist in placing emphasis on a specific element in the frame. This can be accomplished by using longer focal lengths, wide apertures or a combination of both.
In any event, the key is understanding how the camera “sees” depth of field differently than you do and what you can do to overcome or take advantage of this fact, depending on what you want to achieve.
A practical—not literal—photographic definition of dynamic range is the measurable difference, in exposure value (EV)—between the brightest and darkest areas of a scene in which detail can be rendered. There’s some disagreement on the exact amount, but the consensus view is that the human eye has greater dynamic range than any commercially available photographic medium, be it a digital sensor or film. While generational improvements in modern digital sensors have closed the gap, your camera is still unable to match the effective dynamic range of your eye. (A tip within a tip: with digital cameras, the lower the ISO value selected, the greater the dynamic range.)
You can test the principle that your eyes have a greater dynamic range than your camera. Go out on a bright, sunny summer day as close to high noon as possible; take your digital camera with you. Look at a scene with bright highlights and deep shadows with your eyes. You will almost certainly be able to resolve detail in both areas with the naked eye. Now, take a photograph of the same scene and take a look at the exposure histogram and the LCD image itself. I can all but guarantee you that either the brightest highlights or the deepest shadows (or both) will be blown out/blocked up; in other words, they will be without detail. The dynamic range of your camera—but not your eyes—has been exceeded.
There are a number of ways around this dynamic range problem (for instance, this is, in essence, what high dynamic range (HDR) imaging was designed to accomplish), but the point is that it’s important to recognize when and how a scene’s dynamic range surpasses what your camera can handle in a single exposure so you can make an intelligent decision about what, if anything, to do about it.
Once you recognize the difference between your camera’s “sight” and your own, you’ll be in a position to understand how to either (1) take advantage of that distinction (if you want things to appear differently than the scene your eye sees) or (2) compensate for it (if you want to render your image in a manner that mimics how the unaided eye sees things). There’s no right or wrong choice; it’s entirely a matter of making an informed decision and making your creative vision come to the fore.
Thursday Tips is written by Kerry Mark Leibowitz, a guest blogger on 1001 Scribbles, and appears every other Thursday. To read more of his thoughts on photography, please visit his blog: Lightscapes Nature Photography.