[B][COLOR=darkgreen]No.8[/COLOR][/B]: What's the fuss about SWD?

[B][COLOR=darkgreen]SWD[/COLOR][/B] stands for [COLOR=darkgreen][B]SuperSonic Wave Drive[/B][/COLOR]. It's Olympus' own technology and is used in three areas across the company's camera body and lens products.

Olympus has developed and patented several technologies that centre around the transmission of mechanical energy through high frequency vibrations. These vibrations are at so-called 'supersonic' frequencies in excess of around 25KHz, and they project wave forms through otherwise solid media, hence the marketed name of 'SuperSonic Wave'.

The first application was the [COLOR=darkgreen][B]SuperSonic Wave Filter[/B][/COLOR], or [COLOR=darkgreen][B]SSWF[/B][/COLOR], for dealing with dust on the camera sensor. The SSWF is a circular optically clear filter placed in front of the camera's image sensor in all Four Thirds and Micro Four Thirds cameras from Panasonic, Leica, and Olympus to date. Piezo-electric transducers vibrate at high frequency, forming a wave vibration in the filter. Dust resting on the filter is accelerated by the wave until it is literally flung off, rather like flicking a table cloth to get rid of crumbs. It's far more effective than shaking the sensor or vibrating a filter in a simpler way, which other camera makers present as an alternative anti-dust measure.

Olympus next used its SuperSonic Wave technology to drive its new in-camera image stabilisation system in the E-510 DSLR, launched in March 2007. This time the wave energy is harnessed to act like a linear motor in two dimensions, enabling the sensor to float in a near-stationary position while the camera body is still moving about it. Similar technology has been used ever since in all Olympus Four Thirds models apart from the E-4xx range.

In October 2007, at the same time that the Olympus E-3 flagship DSLR was launched, Olympus unveiled its SuperSonic Wave Drive lens autofocus system. SWD motors operating the AF system were initially introduced in the Mark 2 version of the 50-200 SWD Zuiko Digital zoom, and the E-3's standard zoom, the 12-60 SWD. The third lens to be fitted with an SWD AF motor was the 14-35 f/2, which started to ship in early 2008.

SWD focus motors are [COLOR=darkgreen][B]'ring' motors[/B][/COLOR]. There isn't much new in the basic concept of ring-type ultra-sonic vibration-driven focus motors. Canon has been making its USM (Ultra Sonic Motor) lenses since the mid-1980s. The idea is that you have two rings that are situated against each other. By vibrating one (the stator) the second (the rotor) rotates. The stator ring has fine ridges or teeth that work like legs when they are vibrated, pushing the rotor ring. Such motors can be very precisely controlled. Another benefit of all 'sonic' ring motors, including SWD, is that the noise they make is inaudible to the human ear. There is no gearing, which is another potential source of mechanical noise.

To date, SWD ring motors are large diameter and the rings are of similar diameter to some lens elements. The Zuiko Digital 50-200 lens optics had to be slightly modified to accommoate the new SWD ring motor, for example. Ring motors can also be made much smaller, into micro motors.

Olympus SWD ring motors operate on a similar principle, but Olympus claims to have made the system faster and more efficient by optimising the vibration of the stator ring. Its that 'W' for 'Wave' that is the key. By inducing an elliptical wave vibration in the stator, the energy transmitted through to the stator is higher, so the rotor can be rotated faster. This is why Olympus can claim SWD lenses have the fastest autofocus actions of any comparable camera lens. In reality, the speed of the motor is only part of the equation that results in focusing speed, but SWD lenses do have a head start.
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