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ZOOM
LENS
TECHNIQUE
Why zoom shots and tracking shots differ in perspective.
By ARTHUR GRAHAM, BKS*
^he idea OF combining different focal lengths within one lens goes back many years in the history of photography, and lenses were in fact de¬ signed so that by using all the components one focal length was obtained, and then with certain compo¬ nents detached this focal length would be increased, although with a smaller f/number. This uncom¬ bined lens frequently suffered from optical defects. In the early nineteen-thirties the idea was taken a step further in lenses intended for motion picture production, which allowed the focal length to be changed not by the removal of any components but by the movement of the parts of the lens in rela¬ tion to one another. They still had the disadvan¬ tage however of the necessity of using a small aperture if a “zoom” was made, in order to obtain acceptable quality, “zoom” being the word used to describe the action of changing continuously from one focal length to another. The film indus¬ try did not show a great deal of interest in these lenses, possibly because of the price (which was high) and also because of the exposure difficulties inherent in their use; and as a result, no further work was undertaken along these lines until after World War II. Lenses were then made in which the widest aperture could be used throughout all the varying focal lengths. Television companies quickly realized that this new piece of equipment was ideally suited for a large amount of the work they had to undertake, if indeed their demands had not in fact stimulated its production. And from
Reprinted by permission from Vol. 41, No. 3, of British Kinematography. Author Graham is Films Officer for Bowater Paper Corporation. Ltd.. London.
WITH HIS ZOOM-EQUIPPED Bolex mounted on the bed of his station wagon, cinematographer Roy Zeper has the dual advantage of both the zoom and tracking shot, depending on the demands of the script.
there its use has spread into all branches of film making.
The effect of altering the focal length of a lens while filming — in other words “zooming” — is to change the angle of view. If the lens is set at a wide angle and is then changed to a narrow angle, the result is a concentration on some detail of the original long shot. Reversing the process and going from a narrow angle to a wider one gives the effect of placing a detail seen at the start into a wider setting.
The usual method employed in film making to achieve these two effects has been the tracking shot. The camera is mounted on a truck— known as a “dolly” — and is moved backwards and forwards as required in relation to the objects being filmed. It may also be mounted on a crane in which case the movement of the camera can be vertical as
FIG. 1 — long shot — showing perspective before tracking or zooming.
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AMERICAN CINEMATOGRAPHER, JANUARY, 1963