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J. Perelman
"Entertaining physics". Book 1.
Chapter 7. Rays of light


Many do not know that the photographic apparatus can be arranged and without a magnifying glass (lens), using just a small round hole. Images obtained with the less bright. An interesting modification of this camera without a lens is “slit camera, in which, instead of holes, there are two intersecting slits. In front of the camera placed two plates; one made a vertical slit in the other horizontal. If both plates are adjacent to each other closely, the image is the same as that of the camera hole, i.e. undistorted. Quite otherwise occur if the plates are at a distance from one another (they purposely make mobile); then the image funny way distorted. It turns out more of a caricature than a photograph.

Photo-caricature obtained using a slit camera. The image is stretched horizontally.

Caricature photo, stretched vertically (received slit camera).

What accounts for this distortion? Consider the case where the horizontal slit is in front of the vertical.

Why slit camera gives a distorted image.

Through the first slit With the rays of the vertical lines of the shape D (cross) will take place through a simple hole; back slit does not change the progress of these rays. Therefore, the image of the vertical line will be on the frosted glass in A scale which corresponds to the distance of the glass from A wall C.

Otherwise it will be displayed on the glass horizontal line at the same location of cracks. Through the first (horizontal) slot rays pass freely, without crossing, until they reach a vertical slit; through the slit rays will pass through the hole and give A frosted glass image scale, which corresponds to A distance from the second partition Century

In short, vertical lines, with this arrangement of slits, as if there is only one front slit; for horizontal, on the contrary, only one rear. As well as front slit farther from frosted glass, rather than the rear, all vertical stretch should get on the glass in A larger scale than the horizontal: the image will be stretched in the vertical direction.

On the contrary, when the reverse arrangement of the slits should get image elongated in the horizontal direction (compare the first two images).

It is clear that the oblique placement of the slits will get distortion, respectively, of another kind.

This camera can be used to obtain not just caricatures. It is also suitable for more serious practical purposes, for example, to prepare options for architectural ornaments, patterns for carpets, Wallpaper, and so on, to obtain ornaments and patterns, optionally stretched or compressed in a particular direction.

Entertaining physics J. Perelman


System Orphus


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