In digital SLR cameras, image stabilization is based on the sensor-shift method or the lens-shift method (Figure 1). α series cameras use the sensor-shift method which stabilizes the image by moving the image sensor inside the camera body. Because the amount of drive required to correct camera shake varies according to the lens, focal-distance data from the lens is required to control the adjustment. With the α series, data is exchanged via the contact points between the body and the lens, enabling the stabilization process to be controlled within the body.

Figure 2 is a block diagram of the image stabilization system. The α series image stabilization system (SteadyShot INSIDE) is controlled by a microcomputer, which repeatedly carries out the digital servo processes (described in 1. through 3. below) at a specific frequency.

• Angular velocity signals from the shake detector (Gyroscope sensor) are amplified in an analog signal processing circuit and converted into digital signals by the control microcomputer. The resulting angular velocity signal input is then converted into shake angle data through signal processing. Information about the focal length of the interchangeable lens is then used to convert the shake angle into shake distances on the image sensor.
• Positioning signals from the position detector (a magnet that moves in unison with the image sensor and an opposing hall sensor) are amplified in an analog signal processing circuit and converted into digital signals by the control microcomputer.
• The amount of image sensor movement required is calculated from the amount of shake and the current position. The system then drives the actuators accordingly.

As already stated, α series cameras provide image stabilization by moving the image sensor inside the camera body. Because stabilization performance becomes compromised if there is any motion within the image surface or along the optical axis during the stabilization process, Sony decided to use ultrasonic linear actuators to drive the stabilization system. These ensure that image sensor motion is smooth.

An ultrasonic linear actuator consists of a piezoelectric element (which expands or contracts in response to voltage changes), a shift that fixes the actuator to the piezoelectric element, and a slider through which the image sensor is attached. Because the slider is linked to the telescopic shaft by friction, the movement can be driven without shaking. The piezoelectric element controls the sliding movement of the slider by applying appropriate velocity variations as the slider moves back and forth. In this way, the back and forth motion of the actuator is converted into linear motion by the slider.

The photo shows the actuators actually used in the α700 with an APS-C size image sensor and the α900 with a 35mm full-frame image sensor. The actuator used to drive the full-sized image sensor in the α900 is capable of moving about 1.5 times more mass than the actuator in the APS-C. By developing this new device, Sony was able to create the world's first 35mm full-frame digital camera with an image stabilization system built into the body.

The image stabilization unit contains two actuators to correct camera-shake in two directions: pitch and yaw. Figure 3 shows the structure of the image stabilization mechanism for a full-sized image sensor.

The image stabilization unit is comprised of various parts (as shown in Figure. 3). The base plate attaches to the camera body and to this base plate the yaw actuator is attached. The actuator is sandwiched between the slider and the cap. A single slider is used for both the yaw and pitch sides. The pitch actuator is incorporated into the image sensor holder and is fully integrated with the slider. This allows it to move freely relative to the camera.

When the image stabilizer is activated, data output from the two hall sensors on the base plate is used to detect the position of the image sensor. Camera-shake detected by the angular velocity sensor is then cancelled out by controlling the direction of motion.

In this basic drive structure, the small size of the drive unit relative to the image sensor supports extremely precise motion without shaking.

Users want digital SLRs that are both highly compact and energy efficient. Sony aims to meet these needs by further enhancing its SteadyShot INSIDE image sensor shift image stabilization system. Key areas requiring improvement include reducing the power consumption of actuators and devices, the scaling down in size of mechanical components, and improving the image sensors. Sony has expertise in all of these areas, including mechanical components, control devices and image sensors and will continue to use its advanced knowledge to create exciting new digital SLRs.