Early Work In Photography
A Text-book For Beginners
Forfatter: W. Ethelbert Henry C. E., H. Snowden Ward
År: 1900
Forlag: Dawbarn and Ward, Limited
Sted: London
Udgave: 2
Sider: 103
UDK: IB 77.02/05 Hen
Illustrated with an actual negative and positive, and numerous
explanatory diagrams throughout the text
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50
Early Work in Photography.
maiden aunts as well as to candle flames, and that this is the
reason why the lens image is inverted—no witchcraft about
the lens. ,
Let us now put our candle in a lantern or behind a piece
of tin or card-board having an opening an inch square
covered with a piece of ground glass or waxed paper. When
this illuminated square is p aced opposite the pin-hole and
three inches distant, it will throw upon the glass
screen, if that is also three inches distant, an image exactly
one inch square. Why is it exactly one inch square ?
Because light travels in straight lines, thus.
If we now move the ground glass screen to six inches
distance we shall find that it bears an image occupying four
square inches, or two inches by two. The reason seems ob-
vious, for we double both the length and the breadth of the
image We shall observe moreover, that the image in this
case is much less bright than it was in the previous case,
In fact, it is exactly one-fourth tlie brilliancy, and for a very