The Welch Allyn 3.5V Autostep Coaxial Ophthalmoscope set features Welch Allyn's Patented Coaxial Vision optics, and 68 lenses in single-diopter steps (+38 to -30) and 18 unique aperture/filter combinations. Halogen lamp illumination insures true tissue color and a Polarizing filter virtually eliminates corneal reflection. The universal rechargeable handle powers has an adjustable rheostat control. Its free-floating reserve setting allows optimal intensity and battery life. The convenient built-in charger allows you to plug into any conventional wall outlet for overnight recharging. A long-lasting rechargeable nickel-cadmium battery is included. Its smooth, non-abrasive knurled finish ensures a no-slip grip. Its chrome-plated brass handles provide durable, long-life construction. It has a safety switch to prevent accidental draining of the battery and metal head connectors for durability.