Magazine article American Cinematographer

Magazine article American Cinematographer

## Article excerpt

(Inquiries are invited relating to cinematographic problems. Address: Q. & A., AMERICAN CINEMA TOGRAPHER, P. O. Box 2230, Hollywood, Calif. 90028.)

Q I wish to use before-the-lens mattes or masks for split-stage and other double exposure effects. Can you give me some kind of mathematical formula for calculating the correct distance before the lens to place the masks relative to focal length of lens and aperture used in making the picture? I am using a 16mm Auricon Cine-Voice camera.

A I do not know of a mathematical formula for making such a calculation; however, it is desirable to position the mattes so that they are slightly out of focus. This will give a soft blend-line at the split and consequently lap each exposure, making the split invisible. The approximate position can be arrived at by referring to the lens depth-of-focus chart and placing the mattes inside the expected depth of field for the lens stop being used.

Q What kind of meter is most commonly used in studios for footcandle measurements?

A There are quite a few footcandle meters on the market, all good. The one I use is the Spectra. It is calibrated with a scale from O to 300 footcandles and a range extended by a 1OX multiplying slide which will allow you to read from O to 3000 footcandles.

W.S.

Q On TV documentaries I often see a large-scale map, or a scene of a painting, or similar still picture which is zoomed in on to capture only a small segment of the map, or a small figure in the picture. Is this work done in the camera?

A The professional way to accomplish the kind of zoom shot you describe is to employ an expensive animation stand which allows the camera to be brought closer to the subject while simultaneously adjusting the lens focus by means of an appropriate linear cam. You could improvise the equivalent by suitably mounting your camera on a horizontal track and having an assistant adjust the distance setting on the lens in accordance with pre-measured marks on the track. …

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