A convex lens forms a real image of a small object on a screen placed at a distance of 0.50 m from the lens. The observer then holds one of his spectacle glasses between the convex lens and the screen and 0.05 m away from the lens. The screen is now shifted 0.15 m nearer to the lens to refocus the image. Find the focal length ot the spectacle glass. ls the man long or short sighted?
