Crossword puzzle clue "telescopic part"

the lens nearest the eye in an optical instrument

a fine wire at the focus of an optical instrument, crossing the field of view, to aid in positioning or measuring, also CROSSWIRE

a piece of transparent matter with one or both surfaces curved to cause regular convergence or divergence of rays passing through it

pertaining to the lore, the side of a bird's head, also LORAL

to do something in a specified way