If a luminous object is placed at a distance greater than the focal length away from a convex lens, then it will form an inverted real image on the opposite side of the lens. The image position may be found from the lens equation or by using a ray diagram provided that it can be considered a "thin lens". For a lens of focal length f =20 cm corresponding to lens power P =5 diopters an object distance of o = 30 cm will produce an image at i = 60 cm The linear magnification will be M = -2 If the lens equation yields a negative image distance, then the image is a virtual image on the same side of the lens as the object. If it yields a negative focal length, then the lens is a diverging lens rather than the converging lens in the illustration. The lens equation can be used to calculate the image distance for either real ...
Optics for Optometry