The key dimension for refracting astronomical telescopes is the diameter of the primary lens, which is 36 inches at Lick and 40 inches at Yerkes. However, my u

The key dimension for refracting astronomical telescopes is the diameter of the primary lens, which is 36 inches at Lick and 40 inches at Yerkes. However, my understanding is that the Yerkes lens has suffered cracks around its perimeter and the telescope has been stopped down with baffles to mitigate the optical problems these cracks would otherwise cause, such that presently the Lick telescope has a larger clear aperture.