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plate, lens, angle, focus, circle, drawing, plate-holder, mirror, anamorphosis and disk

ANAT1ORPHOSOPE. — An optical toy, consisting usually of a vertical cylindrical mirror in which a distorted drawing or Anamorphosis.

ANATIORPHOSIS.—The name anamorphosis has been given to two sorts of pictures, dis torted according to a certain law, and which are of such a grotesque appearance that it is often impossible to recognize the subject of them; while viewed with a proper apparatus, they appear regular and take their normal appearance. One sort is designed to be viewed by reflection, the other sort is reconstituted by means of a special apparatus and rotatory motion. Until recently these pictures have been drawn approximately from the reflection of the object as seen in a con vex mirror, whose position was indicated on the drawing, and which restored it to its real form. M. Fenant conceived the idea of employing photography for obtaining these pictures. Fig. 27 reproduces a photoanamorphosis from a negative by M. Frenant. If a cylindrical mirror be placed upon the black circle shown in the drawing, the photograph will appear in its original form. Our illustration gives a portrait, although the features are hardly recognizable. Indeed, a great deal of fun can be had by making portraits of friends and relatives, and trying to recog nize them without the use of the cylindrical mirror. Similar pictures may be obtained by photo graphing the drawing or subject reflected in a cylindrical concave mirror placed perpendicular to the drawing or in front of the subject. The second sort of anamorphosis is produced by the distortion of the picture in the sense of one of its dimensions. To reconstitute it, it is caused to rotate rapidly, at the same time that a disk, perforated with a slit, through which the picture is observed, is rotated in front of it at a slightly different speed.

The apparatus invented by M. A. Linde for producing the anamorphosis is shown in Figs. 28 and 29. G is a provided with a revolving plate-holder, T; H is a revolving disk, whose movement is made to bear a certain relation to that of the plate-holder by means of the band, f, and pulleys, D, D. The whole is set in operation by a clock work and the band, F. A is the axis of the camera, B that of the plate-holder, and C, that of the revolving disk.

On this disk is fixed the picture of which it is desired to make an anamor phosis. The relative mo tions are so regulated that when the plate-holder has made a complete revolution, the disk has turned through an angle of 6o to 8o degrees in the opposite direction. Between the plate-holder and the objective is a diaphragm pierced with a slit io m.m. wide. The action of the light on the plate takes place through this slit. The negative obtained, prints are made on salted paper and rendered transparent; they may then be viewed in an ordinary apparatus such as is used for reconstituting the ordinary anamorphosis of this class.

ANAPLANATIC.—Same as Aplanatic (g. v.).

ANASCOPE.—An optical arrangement permitting one to view the camera image the right side up ; that is to say, not inverted.

ANASTICMATIC.—This term has been applied to lenses corrected for astigmatism. The term, however, is a pleonasm. Stigmate means, literally, a focus, a point where light rays converge to. means a failure to concentrate at one point. An-astigmate is where this failure is corrected. Consequently the lens is mate, a term that would appear to be simple and more correct. Antastigmatic, or opposed to astigmatism, is also employed for the same meaning.

ANGLE.—Literally the opening between two lines which meet one another. Optics have angles of aperture, of incidence, of reflection, of refraction, of deviation, and of polarization. See under these respective headings.

The width of the angle of a lens is determined by the relation of the focal length to the image given, and lenses are thus termed narrow, mid or wide angle lenses, accordingly. To de termine the width of angle of a lens, divide the base line of the plate by the equivalent focus of the lens (see Focus). Having found this out, it will be easy to determine the angle of view in cluded upon the plate by reference to the following table by Clarence E. Woodman : Let us take, for example, a lens with an equivalent focus of 15 inches and we require to know the angle of view included upon a io x 12 plate. The base-line here is 12 inches. Twelve divided by 15, the equivalent focus, gives 1.25, corresponding, as shown in the aboVe table, to 64 degrees.

The following method of measuring the angle of view included by a lens is given by Burton: Focus the sun on the center of the plate some time when it is pretty near the horizon. The smallest top is inserted, and the camera is slowly swiveled till the image of the sun disap pears. The spot where it was last seen is marked, and the camera is then turned in the opposite direction, and the spot where the sun was last seen is again marked. The distance of the two marks is the diameter of the circle covered. To find the angle the following construction is made : A line (AB) (Fig. 3o) is drawn equal to the focal length of the lens. At B a line BD is erected perpendicular to AB. BD and BC are each made equal to the radius of the circle. AC and AD are then joined. The angle CAD is then measured with a protractor or otherwise, and is the angle of the lens, and the diag onal of the largest plate that can be used. To discover if the lens will cover any given size of plate, the circle is drawn out on the paper, and it is found by actual experiment whether or not the plate will come within it. For example, the diameter of the circle is i6 inches. If it is desired to find if a plate 12 x io inches will come within it, the plate is laid on the circle, and it is found that it just comes within it. With a larger plate the corners project.

It is not advisable to try to make a lens cover too large a size of plate, as the result will be unpleasant dark corners. In fact, no little advantage is gained by using a lens for a size smaller than that for which it is intended—for instance, a 5 x 4 lens for a quarter-plate.