On now considered the principle is based and the effect of those “wonders of shadows”, which appeared sometimes in the movies.
“Wonders of shadows are cast on the screen, shadows moving figures are presented to the audience (armed two-tone glasses) in the form of bodily images, convex protruding in front of the screen. The illusion is achieved here by using a two-tone effect of stereoscopy. The subject, the shadow of which it is desirable to show, is placed between the screen and the two placed near sources of light - red and green. On the screen you get two colored shades - red and green, covering part of each other. The spectators look at these shadows are not directly, but through the glasses with flat glasses - red and green.
Now it was explained that under these conditions generated the illusion of corporeal image, speaking ahead of the display plane. Illusion, achieved miracles of shadows, extremely funny: sometimes it seems that the thrown object flying straight at the viewer;
some giant spider walks on air in public, making her involuntarily scream and turn away. The equipment here is very simple; it is clear from the figure below, where RL and Cu mean green and red lamp (left); P and Q are objects placed between the lamp and the screen; p and q with icons PLN and Cu - colored shadows of these objects on the screen; P1 and Q1 are places in which sees these objects the viewer looking through the colored film - green (PLN) and red (CR). When the fake “spider” behind the screen is moved from Q to P, the viewer think that he runs from Q1 to P1.
The secret wonders of shadows.
In General, the approximation of the object behind the screen to the light source, causing the increase of the shadow on the screen, creates the illusion of slipped on easily subject from the screen at the viewer. All that the audience seems to be flying at them from the screen moves actually in the opposite direction - from the screen back to the light source.