2 1-7 according to geometrical optics1/f =1/u+1/v, the image distance is about 20cm (about equal to the focal length f). According to Ruili standard, the distance between two image points is 60 * 20 *10/(50 *1000) = 0024 mm, which is the radius of the diffraction point. Therefore, the diameter of diffraction spot is 0048 mm, suggesting that when asking questions, it is easy to answer only one question at a time.