210 SEC. 7. LIGHT. 



landscape Its aperture is limited by a diaphragm plate placed at a distance 

 of ^ its focal length in front of the lens; the stops provide apertures from 



/ f 



- to . Correction of chromatic spherical aberration is obtained by the foci 



and forms of the lenses employed. 



The angle included extends to upwards of 70, and though marginal dis- 

 tortion of image is not entirely avoided, it is perhaps counterbalanced by the 

 increased brilliancy of image and equality of illumination, due to the absence 

 of all disturbing or reflex images. 



4. A wide angle rectilinear lens of \\" diamter, and 7" equivalent focal 

 length for 12 x 10 pictures. 



This lens is constructed upon the same general principle as the symmetrical 

 3" combination already described, with this difference, that the lenses com- 

 posing it, though of similar forms, are of proportionately smaller diameter, 

 i.e., they are thinner, and being placed nearer together, they transmit more 

 oblique pencils, or a larger angle of picture is included, as much as 90, with 



apertures {- to . 



This instrument is designed for photographing objects in confined situations, 

 such as interiors of buildings, monuments, &c., where the camera cannot be 

 removed to a greater distance. It produces images free from distortion. 



962. Apparatus for producing pictures in permanent pig- 

 ments. 



The Autotype Process. 



If a negative in half-tones be placed under a paper coated with gelatine 

 pigments of any kind and potassium dichromate, and then be exposed to 

 light, the action that takes place is, the gelatinous film is rendered insoluble, 

 and depths varying according to the intensity of the light passing through 

 the various portions of the negative. If the paper were at this stage exposed 

 to the action of hot water, it would be found that the soluble portions lay 

 between the exterior surface of the film and the inner surface of the paper. 

 In order to develop the picture, it is transferred by simple atmospheric pres- 

 sure to a zinc plate or other temporary and impervious support. The original 

 paper peels off, and the development takes place by the simple application of 

 hot water, the shades of the image being formed of different thickness of 

 gelatine and pigment. The image may be retransferred from the temporary 

 support, or if developed on a paper support may be left as it is, in which case, 

 unless the negative be reversed, the picture will appear reversed. 



962a. Apparatus for producing photographs in permanent 

 pigments ; consisting of, 



Registering pressure frame. 



Plates of zinc, porcelain and opal glass (the plates having upon 

 them : a. The sensitive tissue readv for development, b. The 

 supporting paper stripped off. c. The picture partly developed. 

 d. The picture ready for transfer). 



Reservoir for hot water, with means of keeping it warm, and 

 grooves for the plates. 



Zinc tray for development washing, &c. 



Wooden stool and squeezer for the mounting of the exposed 

 sensitive tissue. The Autotype Company. 



