Early Work In Photography
A Text-book For Beginners

CHAPTER VII. FACTS ABOUT LENSES 0 O part of his outfit puzzles the average photographer | / so much as the lens, and ignorance of some of its -LC simplest properties exists even among advanced workers. This seems to be because the elementary principles have not been carefully explained, and because the meaning of a few technical terms has not been learned. There is a great deal of “ superstition ” about the lens, and many fallacies are believed about it; but its operations are based on the unchangeable laws of the universe, and the first of these is that " like causes, acting under like conditions, produce like effects.” If photographers would always realise tilis, they would meet fewer difficulties. To understand the principles of the lens it is well to do a little experimenting witli a pin-hole; for the fundamental laws are the same in botli cases. . , Take your camera, screw out the lens and put in its place a piece of tin or fine card-board through which you have made a hole witli a fine brad-awl or a darning needle. Go into a fairly dark room and place a lighted candle witli the centre of its flame three inches from the hole (which we will now call a pin-hole). Adjust your camera so that the ground glass screen is three inches from the pin-liole, and you will be able to see on the screen an image of the candle-flame exactly the same size as the original flame, but inverted. Why is it inverted? Because liglit proceeds in a straiglit line (Fig. i); and cannot work round corners (Fig. 2). Fig. 1. Fig. 2 If this is not clear at once, think it over until it becomes so. Then remember it is a law, applying to church steeples and