A Manual Of Photography
Forfatter: Robert Hunt
År: 1853
Forlag: John Joseph Griffin & Co.
Sted: London
Udgave: 3
Sider: 370
UDK: 77.02 Hun
Third Edition, Enlarged
Illustrated by Numerous Engrabings
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158 SCIENTIFIC INVESTIGATIONS ON PHOTOGRAPHY.
over it. The openings in this moveable plate are parallel to
each other. They are seven in number, each opening being
one-half of the following one, and double that of the preceding
one. Thus, after the operation of the light, we have seven
separate images, the different intensities of which represent the
action of light during the intervals of time in the geometric
progression of—1: 2 : 4: 8 : 16 : 32 : 64.
22.
23.
The box in which the plate or paper is placed for experiment,
is pierced with holes, and these correspond with the slits in A B.
(fig. 23). By inclining
the instrument, which
can be very readily
done to any degree by
means of the curved
arms c DE, any velocity
can be given to the
falling screen, and thus
the plate be exposed to
the action of the che-
mical rays for any
period of time we