Monday, October 11, 2010

Creative Zooming

Zoom lenses are popular with most photographers because of the added versatility they offer compared to fixed-focal-length(prime) lenses. A zoom lens allows the photographer to choose the point of view and then vary the perspective/background by changing the focal length and distance to the subject with a single lens. Zooms also let photographers change the subject size in the image and/or the framing without physically moving to get closer or farther away from the subject.

In addition to the conventional selling points, zoom lenses offer important creative possibilities not available when using prime lenses. One creative use of zooms is to change the focal length during a long exposure. The result is a subject centered in the frame appears to be exploding or imploding depending which direction the focal length changes. This technique has endless possible variations all starting from the same point.

A slow shutter speed is required, preferable at least ½ second or longer. Enough time is needed to smoothly change focal lengths during the exposure. If a sharper main subject is desired, part of the exposure should be at a constant focal length and only part of the exposure zoomed. Another way to get a sharper main subject is to use flash. The long shutter speeds required can be achieved by combinations of: low ISO speeds, small f-stops(f/16-f/22) and use of polarizing and/or neutral-density filters.

This technique is best accomplished with the camera locked down on a solid tripod. Hand-holding will produce much less predictable but possibly more interesting results. Unlike the usual compositional advice, zooming during exposure normally looks best with the main subject centered in the frame(that is where the explosion/implosion lines converge).

Every photographer should experiment with all of the variables to find the results they prefer. Once that result is achieved this is a very repeatable technique. Always try variations for different subject matter. If using flash, try both first-curtain and second-curtain synch to see the difference and decide which is preferred. Try zooming both short-to-long and long-to-short-the results will not be the same.

Another variation of this technique is to shoot many exposures at slightly different focal lengths and combining all exposures into one image(this could be done on one frame of film). The result will be a “stepped” zoom look without the streaks of a continuous zoom. This is also best done with the camera on a tripod to keep framing and focus constant.

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