Automatic Focus
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.
Read more about this topic: Lenses For SLR And DSLR Cameras
Famous quotes containing the words automatic and/or focus:
“What we learn for the sake of knowing, we hold; what we learn for the sake of accomplishing some ulterior end, we forget as soon as that end has been gained. This, too, is automatic action in the constitution of the mind itself, and it is fortunate and merciful that it is so, for otherwise our minds would be soon only rubbish-rooms.”
—Anna C. Brackett (1836–1911)
“When Western people train the mind, the focus is generally on the left hemisphere of the cortex, which is the portion of the brain that is concerned with words and numbers. We enhance the logical, bounded, linear functions of the mind. In the East, exercises of this sort are for the purpose of getting in tune with the unconscious—to get rid of boundaries, not to create them.”
—Edward T. Hall (b. 1914)