The sciopticon manual, explaining lantern projection in general, and the sciopticon apparatus in paricular (1877)

Record Details:

Title:
The sciopticon manual, explaining lantern projection in general, and the sciopticon apparatus in paricular
Date:
1877
Publisher:
Philadelphia, J. A. Moore
Volume:
The sciopticon manual, explaining lantern projection in general, and the sciopticon apparatus in paricular
Leaf #:
00020
Language:
English
Collection:
Books
Format:
Books
Contributor:
University of California Libraries
Sponsor:
MSN
Coordinator:
Media History Digital Library
Description:
Date Added:
July 19, 2022
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SCIOPTICONMANUAL. 11 SIZE ON THE RETINA. A A (Fig. 2) represent* the visible portion of the sclerotica of the human eye, which is a camera obscura in perfection. 1 I represents the iris (or window shutter), in the middle of which is the pupil (or aperture). As the retina is only about half an inch behind the optical centre, it follows that the images of distant objects upon it must be xfy- 9. very minute. For example, the figure of a man 6 feet high, seen at a distance of 40 feet, produces an image upon the retina the height of which is about y^th part of an inch. The face of such an image is included in a circle whose diameter is about y^th of the height, and therefore occupies on the retina a circle whose diameter is about the -j-j^th part of an inch; nevertheless within this circle, the eyes, nose, and lineaments are distinctly seen. The diameter of the eye is about T ^th of that of the face, and therefore, though distinctly seen, does not occupy upon the retina a space exceeding ^(j^iuirD^^ °f a square inch. How infinitely delicate must be the structure of the retina or canvas on which this exquisite miniature is delineated to receive and transmit details so minute with such marvellous precision ! SIZE IN THE: PHOTOGRAPHIC CAMERA. A man G feet high, standing for his picture 10 feet from a camera tube whose lenses require the screen of ground-glass adjusted to 5 inches, gives a 3 inch picture. For we have (in inches) 120 : 5 : : 72 : x hence x = * = 3.