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J. Perelman
"Entertaining physics". Book 1.
Chapter 9. Vision one and two eyes

THE BEST PLACE IN THE CINEMA

Frequent visitors to cinemas noticed, it is likely that some of the paintings were distinguished by the extraordinary relief: figures are separated from the background and convex so that you forget even about the existence of a cloth and see if the real landscape or live performers on stage.

This relief image does not depend on the properties of the tape itself, as is often thought, and from where the viewer is placed. Cinematic shots although manufactured using very short-focus cameras, but projected on the screen in enlarged form, a hundred times, so that they can be considered two eyes from a distance (10 cm * 100 = 10 m). The greatest relief is observed when we look at the pictures under the same angle as the device is “looked” on his nature when shooting. Then, before us is a natural perspective.

How to find the distance that meets such a favorable angle of view? For this you need to choose the place, first, against the middle of the picture, and secondly, at such a distance from the screen, which is as many times greater than the width of the picture, how many times the focal length of the lens more than the width of the film tape.

For cinematic shots usually are cameras with a focal length of 35 mm, 50 mm, 75 mm, 100 mm, depending on the nature of the shooting. Standard belt width 24 mm For focus, for example, 75 mm are:

(desired length/width of the picture) = (focal length/width tape) = 75/24

So to find the distance at which you need in this case to sit from the screen, just the width of the picture to increase by about 3 times. If the width of the cinematic image 6 steps, the best place for examining these frames are located in 18 steps from the screen.

This fact should not be overlooked when testing various proposals intended to give the stereoscopic films: easy to assign the test to the invention that due to these reasons.

Entertaining physics J. Perelman

 




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