Ten pieces of glass.
Ten elements in eight groups, two of them aspherical, held in an all-metal barrel.
Ten elements
Each one bends the light a little. Together they bring it to a sharp point.
Eight groups
Some elements are cemented in pairs, so ten pieces of glass sit in eight groups.
Two aspherical
Two surfaces are not quite spherical. They correct what round surfaces cannot.
All-metal barrel
The focus ring is metal too, with a long throw for fine focus by hand.