Ocular refraction and the shadow test . e principal focus F,the path of another ray from L through the optical centre O willmeet E F at L which will locate the image of the point L; in the sameway locate the image of the point M at M. It can thus be shown thatlight frorn every point upon the object is directed to its correspondingposition in the image. j^ convex spherical lens creates a real inverted image of an object by focus-ing upon a screen the divergent rays from every point upon the object, the collection of foci creating the image. Take a convex lens L, figure 41, of say ten inches foc
Ocular refraction and the shadow test . e principal focus F,the path of another ray from L through the optical centre O willmeet E F at L which will locate the image of the point L; in the sameway locate the image of the point M at M. It can thus be shown thatlight frorn every point upon the object is directed to its correspondingposition in the image. j^ convex spherical lens creates a real inverted image of an object by focus-ing upon a screen the divergent rays from every point upon the object, the collection of foci creating the image. Take a convex lens L, figure 41, of say ten inches focal lengthand place a lighted candle at its principal focus A, the light will berefracted as parallel rays on emerging from the lens and the image of OCULAR REFRACTION. the candle will be at infinity (practically no image is formedj, if thecandle be placed at the point C twenty inches from the lens, justdouble its focal length, a sharp image of the t^ame will be projectedupon a screen held at C twenty inches from the lens and this image. rure 41. Position and size of image tornied by a convex spherical lens, the object in various positions with regard to the focus of the lens A different character of line joins each object and its image. will be the exact size of the flame. If the candle be removed furtherfrom the lens than twice the focal length say to D thirty inches away,the image may be received upon a screen at D fifteen inches from thelens and the image will be smaller than the flame, in fact just half thesize. If the candle be placed between the positions A and C at is, between the focus and twice the focal length, the image willbe larger than the flame, and more than twice the focal length re-moved from the lens If the candle be placed at E, nearer to the lens
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