55-250 stm 3.5 stops meaning
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These are STM, USM and a more conventional DC motor. Nowadays, there are currently three main types of focusing motor technologies used within Canon lenses. This type of motor was able to provide high torque at low speeds, so there was no need for the gearbox.Ĭlick here to get access to all photography Coupons provided by our site What are the current types of focusing motor? The second type was the novel piezoelectric ring motor. The first was the standard permanent magnet DC motors, connected to a gear train, that was designed to wrap around the optical cell of the lens. Over the next 30 years or so, it became clear that Canon’s designers had got it right, and the other manufacturers converted their systems to follow the Canon architecture very closely by putting the autofocus motor in the lens.Ĭanon introduced the EOS (Electro-Optical System) in 1987, and it included two different types of autofocus motor. Nikon, Yashica, and Pentax produced similar ‘screwdriver’ systems, but the only major manufacturer breaking ranks being Canon, whose designers decided that the right place for the autofocus motor was in the lens. As other manufacturers introduced their own autofocus systems, they generally followed that same architecture.
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In the first really successful autofocus system, which was fitted to digital camera in1985, the motor that drove the focus scroll of the lens was in the camera, with a mechanical ‘screwdriver’ link from the camera to lens. As the usage of DSLRs for video became more popular, Canon introduced STM (Stepping motor) lenses that provided a smoother experience albeit at a slight disadvantage on the speed side. This is what we know today as USM (Ultrasonic motor). Canon autofocuslenses have long focused on speed and not so much on the smooth and quiet operation.