Copying Restorations to the Vertical Deformations 733

image, sensitive, optical, surface, original, lenses, deformation and method

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A triple body camera represented in diagram matic form in Fig. 189 comprises a negative carrier AB and a dark-slide for the sensitive paper AR', which swing respectively round the axes RR' contained in their planes of support. To ensure the intersection of these two planes in M in the plane perpendicular to the optical axis let fall from the optical centre of the objective 0, two levers QR, QR' are fixed to the end bodies of the camera and are pierced with grooves following the perpendiculars at R and R' to the planes AB and A'B'. A gudgeon Q moves without friction in these grooves. This gudgeon is forced to move in a groove PQ of the base, perpendicular to the optical axis, in such a position that the distances OR and PR' are equal.

746. In addition to the already-mentioned applications of the method of rectifying a dis torted image, the same methods make it possible to distort systematically any image so as to obtain, for instance, a transparency which, when projected obliquely (projectors for advertising purposes forming on the pavement in front of a shop window an image which is usually very distorted), will be brought back to normal proportions.

In thus distorting an image and then rectifying it without observing the condition of non deformation, it becomes possible at will to draw out or compress one of the dimensions relatively to the other in any desired proportion.

747. Systematic Deformations. Intentional deformations have been worked out at various times. These are either caricature deformations or one-way deformations (extension or compres sion of one dimension of the model, a square thus becoming a rectangle) to restore to the same scale drawings made on non-proportional co-ordinates, or to adapt decorative composi tions to various uses (carpets, hangings, furni ture, labels of a given product packed in con tainers of various shapes, etc.), or to exaggerate scarcely visible variations (flexions or vibrations of rails or mechanical parts).

748. In addition to the method of working described in § 746, " one-way " deformations may be obtained by mechanical or optical means.

For the mechanical deformation of an original there is used a method similar to that described in § 742 for reproduction without distortion. This principle, similar to that of the anortho scope of Plateau (1829), has been employed by E. Archdeacon (1893), and later by R. Luther (19I0), and the latter has also published a complete study of the possibilities afforded by this method.

Let us suppose (Fig. i88) that the original P and the sensitive surface p are moved at uniform speeds non-proportional to the ultra-nodal dis tances OA and Oa. If the slit F is sufficiently narrow, a sharp image of F will still be obtained on /, but with an extension or contraction, according as the ratio of the speeds is greater or smaller than the ratio of the ultra-nodal distances.

The same result would be obtained if, leaving the original stationary, the focal-plane shutter and the sensitive surface are moved simul taneously. Particular cases are as follow : The sensitive surface is stationary (non-deformed reproduction) ; the sensitive surface and the shutter have equal speeds in the same direction (total compression) ; or the sensitive surface moves at a speed twice that of the shutter (inversion as regards right and left without deformation). In the other cases there may be extension or compression in the direction of the movement, with or without inversion of the image as regards right and left.

For the optical deformation of an original, use is made of cylindrical lenses, the employment of which differs according as it is wished to vary at will the ratio of the two scales of image, or as it suffices to have one invariable enlargement of one of the dimensions with regard to the other.

In the first case, there are employed two con vergent cylindrical lenses of which the axes of curvature are placed at right angles to one another (Vaslin, 1862 ; G. J. Burch, i9o4), and of which the relative positions are caused to vary.

In the second case a photographic lens is fitted with an afocal system formed of two cylindrical lenses, the front one convergent and the rear one divergent, of which the axes of curvature are parallel and of which the relative positions are those of the lenses of a Galilean telescope focussed on infinity for normal sight. Such an arrangement has been applied to " panoramic " cinematography (H. Chretien, 1927), the horizontally-compressed image being restored to normal proportions on the projec tion screen by an identical device fitted on the lens of the projector.

A prism anamorphoser which is adaptable to an ordinary lens to elongate the image in one direction has been produced (R. Petit and A. de Gramont, 1930) on the lines suggested long ago by Brewster, by forming an achromatic prism of which the two elements can he set at an angle such as to vary the degree of anamor phosis.

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