sentences:  Old fast manual focus lenses, just as the Nikkor-S(C) or Nikkor AI-S 50mm 1.4, were historically produced abundantly, and are thus sold relatively inexpensively on the used lens market.Especially outside of the "normal lenses", lens speed also tends to correlate with the price and/or quality of the lens.This is because lenses with larger maximum apertures require greater care with regard to design, precision of manufacture, special coatings and quality of glass.