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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Facts about Lensee.
51
simple reason. We have done nothing to increase the
amount of light passing through the pin-hole; but we have
Fig. 6.
made it cover four times as much space. This applies with
lenses also, and is the basis of one of the most valuable but
least understood of all the laws relating to lens work..
Let us return to our naked candle flame; still leaving it
three inches, and the ground glass six inches from the pin-
hole, and we shall see that the image of the candle flame is
just twice as long and twice as broad as when the ground
glass was three inches distant. It is also just one fourth
the brilliancy of the former image.
Fig. 7.
Let us now move the candle flame to a distance above the pin-
hole; still keeping it three inches from the front of the camera
The image will fall towards the edge of the ground glass,
instead of in the centre, and we shall notice that the image
looks longer and narrower on the ground glass than it would
appear if viewed by the eye placed at the position which