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Zooming during exposureIt is possible to create the impression of movement for stationary subjects by changing the focal length of a zoom lens during a long exposure.

Load a camera with slow film, perhaps ISO 50, or set a low ISO speed on a digital SLR, attach a zoom lens and set the equipment up on a stable tripod. Position the subject, perhaps a person on a bicycle, in the centre of the frame. The part of the subject that is required to main almost sharp must be located at the centre of the frame. In the picture on the left, the headlamp of the motorcycle has been chosen. Focus on this central element with the lens at maximum focal length and then zoom back to check the framing of the wider picture. Select a slow shutter speed and a small aperture – perhaps 1/15 second at f/8 or f/11. Release the shutter while moving the zoom from maximum to minimum focal length. The result should be a reasonably sharp subject at the centre of the image surrounded by a motion-like blur of converging streaks.

It is worth practicing the zooming motion prior to taking images. The first few attempts are unlikely to produce the desired result because the change of focal length must be achieved smoothly and at a rate appropriate to the chosen shutter speed. It is also important to avoid camera shake which will introduce further blurring of the image.

In the image shown here, the motorcyclist was stationary and the bike therefore had to be held upright by placing it on its stand. This allowed the rider to raise his feet from the ground and place them in the normal riding position. The silver lines of the motor-cycle's stand can be seen in the image, although these could easily be removed by digital manipulation.


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