Fig. 2. Optical effects of moving the retinoscope bulb 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) concave mirror effect is produced when bulb is moved down; (right) plane mirror effect is produced when bulb is moved up. (Weinstock SM, Wirtschafter JD: A Decision-Oriented Manual of Retinoscopy. Springfield, IL: Charles C Thomas, 1976.)