749. Anamorphoses. Various arrangements have been suggested (C. Chevalier, 1864 ; Man gin, 1877 ; L. Ducos du Hauron, 1895) for the recording on a plane a complete circle of the horizon in the form of an " anamorphosis," in which the horizon line is figured by a circle and the vertical lines by the radii of this circle. For this purpose " lenses " have been worked out, formed, as shown diagrammatically in Fig. 190, by a shape obtained by the rotation of a curvi line triangle, each of the meridian sections of this " crown " combining the properties of a convergent system and of a total-reflexion prism.
The image of a distant point A is formed in a, the whole of the images being comprised in an annular surface and forming a perspective similar to the distorted annular panorama views provided for tourists in French mountain coun try and affording a view round the whole horizon, but with vertical lines on the subject converted into radii. In France a panorama of this kind is known as a " table d' orientation." It is conceivable that a similar arrangement can be used to project the complete panorama on a cylindrical screen concentric with the axis of the system.
750. Caricature Deformations. Caricature an amorphoses can be obtained by photographing a person (or a bust in alto rilievo) from a very close viewpoint, using a wide-angle lens of very short focal length or a pinhole. All the project ing parts are thus enlarged on a grossly exagger ated scale.
A very curious process pointed out by L. Ducos du Hauron (Trartsformisme photographique, 1899) consists in using, instead (and in the place) of a pinhole, a system of two fine slits differently arranged in two planes not parallel with each other (Fig. 191).
Of the rays of light issuing from each point of the subject, the first slit admits only those which are quite close to the portion of plane defined by the object point in question and the slit of incidence. This plane cuts the slit of emergence in a point around which there is admitted a very narrow beam of rays forming an image of the object point on the sensitive surface. Thus one, and one only, point of the image corresponds to each point of the subject, but the figure formed by the whole of the image points is not similar to the figure formed by the object points. The deformation varies with the relative position of the planes in which the slits are placed and with the direction of the slits in these planes. It is, for instance, possible to obtain a very great variety of effects if each of the slits is mounted in a tube and one tube can turn inside the other.
It is obvious that this arrangement does not readily lend itself to direct photography on account of the small amount of light trans mitted, unless the slits are replaced by cylin drical lenses, but it is easily used for copying an existing portrait. The slits are made in the same manner as described for pinholes (§ 39) and with the same openings.
We must finally mention, as other means for obtaining caricatures, the use of distorting mirrors (such as a sheet of polished flexible metal) or of prisms ; the photographing of a photographic print bent irregularly, or the projection of an image on a bent sheet of sensitized paper, 1 and finally the bizarre effects which can result from the partial melting of the gelatine of a negative warmed whilst in a wet state.