In a simple astronomical telescope, the objective and the eyepiece used respectively, are:

The correct answer is D, a convergent lens and a convergent lens.. A simple astronomical (refracting) telescope uses two convex, that is convergent, lenses. The objective is a convex lens of large focal length and large aperture, so that it gathers plenty of light from a distant star or planet and forms a real, inverted image at its focus. The eyepiece is a convex lens of short focal length that magnifies this image like a simple microscope. The magnifying power in normal adjustment is the focal length of the objective divided by that of the eyepiece, and the final image is inverted, which does not matter for viewing stars. Option A is wrong because a convergent objective with a divergent eyepiece describes the Galilean telescope, which gives an erect image. Option B is wrong because two divergent lenses cannot form a real image of a distant object. Option C is wrong because a divergent objective cannot collect and focus light from far away. Exam tip: astronomical telescope, convex objective of long focal length plus convex eyepiece of short focal length; Galilean, convex objective plus concave eyepiece.