FORMATION OF IMAGE.
Fig. 22.
Let us now see how an image is formed by a convex lens, and suppose that CD is the section of a double convex lens ([fig. 22]), O the optical center, and AB an object at a greater distance from the optical center than double the focal length. Rays will pass out in all directions from the object and some will fall on the lens. A ray from A will pass through the optical center and will not be deviated; others will be incident at various points, for example, E and G, and if we apply the law of refraction we will find that AE and AG will intersect each other and AO at the point A′, provided we do not consider the figure of the lens, forming one point of the image A′ B′; similarly for rays from other points of the object, as, for example, B, we can construct the focus B′, and thus obtain the image A′ B′, which is inverted and smaller than the object AB. The relative size of the image and object will be directly as the conjugate foci, and these can be found at once from the equation of the lens.