The largest refracting telescope in the world is at Yerkes Observatory in Wisconsin. The objective lens is 1.02 mm in diameter and has a focal length of 19.4 mm . Suppose you want to magnify Jupiter, which is 1.38×105 kmkm in diameter, so that its image subtends an angle of 1212∘∘ (about the same as the moon) when it is 6.28×108 kmkm from earth.
What focal-length eyepiece do you need?
