Practice question

**Simple microscope** magnification M = 1 + D/f when image at D=25 cm near point, M = D/f when image at infinity (relaxed eye), f focal length (cm), D least distance of distinct vision 25 cm. For f=4 cm, image at 25 cm, M=1+25/4=7.25, angular magnification ratio of angle subtended by image to that by object at D. In a refracting telescope, the objective lens forms a real, inverted image of the distant object at its focal plane. The eyepiece magnifies this inverted image without reinverting it, so the final image remains inverted unless an additional lens or prism system is used. Substituting values gives