Earth’s Rotation Limits IBIS Performance to 6.3 Stops
In 2016, Olympus Camera made some buzz in the photo world when they claimed that their new camera was capable of an impressive 6.5 stops of stabilization and that the limiting factor was in fact the rotation of the Earth. This was rather surprising given the slow and steady improvement since the first such stabilization systems were introduced in lenses in the 1990s. These only provided a couple stops of benefit. Since then the technology has improved dramatically and the move from film to silicon has allowed it to be incorporated into the camera itself as IBIS.
A major driver of this increase in stabilization performance has been in the gyroscopic sensors used to measure the vibration and control electronics used to correct it. For these types of applications, the accuracy of the zero offset of the gyro sensor is often the limiting factor. Even when perfectly still, noise will cause the sensor to read a small but non-zero value, which will in turn cause the stabilization system to drift. The smaller the drift, the longer the stabilization system can hold an image steady. If there were no noise on the gyro sensor and the stabilization system worked perfectly, it should in theory be able to provide an infinite number of stops of benefit. However, at somewhere around 6 stops of shutter speed increase, the limiting factor stops becoming the electronics, and instead becomes the rotational motion of the Earth!
To illustrate , lets imagine that you are somewhere on the Earth’s surface, pointing the camera due East or West. For simplicity, lets assume you are on the equator, but your latitude doesn’t actually matter for this analysis. There are 86,400 seconds in a day, so Earth rotates at a rate of 2π/86400 radians/second, or 7.27*10^-5 rad/s. That means that your subject, which is presumably stationary on Earth’s surface as well, is rotating at this rate. Your camera, which is using its IBIS system to attempt to keep everything as still as possible, may not realize that you are rotating with your subject and will instead try to zero out any rotation of the camera, including that of the Earth. More technically, the camera is trying to maintain stability with respect to an inertial reference frame, which by virtue of the Earth’s rotation, you and your subject are not.
