f lens object focal point intersection optical axis S1 a) For the thin lens model, derive the equation which relates the following three quantities: . f: the focal length of the lens. . s1: the distance that the object is from the lens. s2: the distance between the lens and the intersection of the rays of light from the object. b) Suppose that f=15cm and that the object is 20m away. At what distance, sz, should the imaging plane be from the lens in order for the object to be in focus? c) Suppose the object moves further away from the lens. Should the imaging plane be moved further or closer to the lens in order for the object to remain in focus