page_title: Lenses for SLR and DSLR cameras
section_title: Automatic focus
hierarchical_section_title: Lenses for SLR and DSLR cameras / Automatic focus
caption_attribution_description: Inside of an 18-55mm Canon EF-S lens
context_page_description: Emphasis is on modern lenses for 35 mm film SLRs and for DSLRs with sensor sizes less than or equal to 35 mm.
context_section_description: Almost all modern lenses for SLRs and DSLRs provide automatic focus. The autofocus sensor(s) and electronics are actually in the camera body, and this circuitry provides electrical power and signals to a motor inside the lens that adjusts the focus. (Some older autofocus systems are based on a motor in the camera body and using a mechanical connection to the focus mechanism in the lens.)
  There are two different kinds of in-lens electronic focus drive motors currently in use, the traditional servo motor and the more modern "ultrasonic" drive systems. These ultrasonic drives go by different names according to the manufacturer, for example USM (Canon), AF-S/Silent Wave (Nikon), Super Sonicwave Motor/SSM (Sony), Supersonic Wave Drive (Olympus), Extra Silent Motor (Panasonic/Leica), Supersonic Drive Motor (Pentax), and Hypersonic Motor/HSM (Sigma). These ultrasonic focus drives typically provide faster focusing than the non-ultrasonic drives, as well as being practically silent and using less battery power.
caption: Electronics of a Canon EF-S lens
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