The advance of photography : its history and modern applications (1911)

Record Details:

Title:
The advance of photography : its history and modern applications
Date:
1911
Publisher:
London : K. Paul, Trench, Trübner & Co., Ltd.
Volume:
The advance of photography : its history and modern applications
Leaf #:
000131
Language:
English
Subjects:
Motion Pictures, Motion pictures--Technology
Collection:
Books
Format:
Books
Contributor:
Media History Digital Library
Sponsor:
Media History Digital Library
Coordinator:
Media History Digital Library
Description:
Date Added:
November 02, 2023
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LENSES 107 symmetrical mass of glass, we obtain the section of a lens, which has the property of uniting all parallel incident rays in one point. (See fig. 29.) Every lens is contained between two curved faces. The connecting line running through the centres of the two surfaces is named the axis of the lens, and the point E (fig. 29), where the parallel incident rays unite, is the focus, while its distance from the lens is the focal length. But not only are parallel rays united in one point by the refraction due to a lens of this kind, the same thing occurs with the divergent rays which issue from any luminous point. The point in which such rays are united is called the conjugate focus of the luminous point. A luminous point S, for example, sends a cone of rays to the lens. After refraction these are united at R. If S be brought near to the lens, B removes further from it ; if S be brought so near that its distance from the lens is twice B the focal length, then the converging point B is equally distant from the lens. If, instead of the luminous point, an object (for example, an arrow B A) is placed before the lens, from each individual point of the object a cone of light proceeds to the lens, and all the rays of one and the same cone con