The dotting lens.
A dotting lens is an auxiliary lens placed in front of the telescope of a focimeter. It images a dot on the center of the lens under test on the scale in the eyepiece. A hole in the dotting lens permits simultaneous meaurement of the sample.
D003261:Contact Lenses / Q000592:standards*; D005139:Eyeglasses / Q000592:standards*; D006801:Humans; D007909:Lenses / Q000592:standards*; D055095:Optics and Photonics