Fig. 3. Optical effects of moving the lens to change the filament to lens distance; this type of retinoscope emits convergent light when the sleeve is moved up. Note the vergences of the emerging rays: (left) plane mirror effect when lens is moved down; (right) concave mirror effect when lens is moved up. (Weinstock SM, Wirtschafter JD: A Decision-Oriented Manual of Retinoscopy. Springfield, IL: Charles C Thomas, 1976.)