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 #:
000137
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 113 to a point focus to be found in the refracted beam of light. When a lens suffers this defect, that is when it has no true focal point, it is said to be astigmatic. To test whether a lens is astigmatic, focus a symmetrical black cross on a white background on the centre of the screen and move the camera slightly to one side ; then if the lens is astigmatic the vertical line will be in focus when the horizontal one is not, and vice versd. This is a far worse fault in a lens than spherical aberration, since it cannot be remedied even by the use of a very small stop, although its effects are not so noticeable under such conditions. A r "A J Fig. 35. single lens forms an image on the screen which is distorted even when stops are used. This can be easily seen by focussing a square as in diagram (35). Then when the stop is placed in front of the lens the distortion is of the pincushion kind (0), when placed behind the lens the image is barrel-shaped (B). It must be understood that the distortion is very much exaggerated in these diagrams. Yet a little care will make it apparent to the most casual observer. Even supposing all these defects removed, there may still be one to look out for, which is of extreme importance in photographic work. Chromatic Aberration. Achromatic Lenses. — When rays of white light pass through a lens from a point on its axis, H