I still don't quite follow the explanation. The duck and I are on the surface of the same body and are rotating together, maintaining a constant distance... why does Earth rotation need to be corrected for?
Ignore the camera. Instead you have a planet (a circle in flatland), a gyroscope (an arrow that always points in the same direction on the page in flatland), and Mr Square.
--> [.]
|
/----\
| |
\----/
Start off at noon, with Mr Square and the arrow at the top of the planet, the gyroscope to the left of Mr Square pointing at him. Now progress time by 6 hours, by rotating the planet clockwise by 90 degrees. Mr Square and the gyroscope will move with the surface of the planet, resulting in them being on the right side of the circle on the page (the gyroscope above Mr Square on the page). Mr Square's feet will be on the surface of the planet, meaning his rotation matched the planet. However, the gyroscope always points in the same direction on the page. It's now pointing at the sky.
/----\
| | -->
\----/-[.]
In conclusion: both Mr Square and the gyroscope move with the surface of the planet - in exactly the same way. However, Mr Square will always be standing (along with everything else on the planet), while the gyroscope always points in the same direction on the page (irrespective of the time of day). A camera using the gyroscope would have to account for that.
We wouldn't have the same issue on a (non-rotating) space station. That's why planetary rotation is blamed.
I asked myself how the gyroscope manages to point always to point to the same direction.
The answer is that only objects moving translational form an inertial frame, rotating objects don't:
> Due to Earth's rotation, its surface is not an inertial frame of reference. The Coriolis effect can deflect certain forms of motion as seen from Earth, and the centrifugal force will reduce the effective gravity at the equator. Nevertheless, it is a good approximation of an inertial reference frame in many low precision applications.
It's about actual gyroscopes (motion sensors), not optical stabilisation. Gyroscopes in cameras are now so good they can pick up earth rotation. Perfect for stabilising image of stars, not so good for stabilising imae of duck translating over those stars. For that you would need optical stabilisation. In-body stabilisation is inertial, not optical.
There was an escape system in the Soyuz rocket that fired if the rocket tilted too much. It was based on gyroscopes.
Once, a launch was aborted just before liftoff. The rocket stayed on the pad and the cosmonauts were sitting in the spacecraft for some time. Suddenly the abort system fired and pulled the capsule from the rocket. They landed safely on parachutes.
It was discovered that earth had rotated and the gyroscope had detected the tilt of the rocket, so it fired the escape system.
> Initially, it was suspected that the booster had been bumped when the gantry tower was put back in place following the abort and that this somehow managed to trigger the LES, but a more thorough investigation found a different cause. During the attempted launch, the booster switched from external to internal power as it normally would do, which then activated the abort sensing system. The Earth's rotation caused the rate gyros to register an approximately 8° tilt 27 minutes after the aborted liftoff, which the abort sensing system then interpreted as meaning that the booster had deviated from its flight path, and thus it activated the LES. The abort sensing system in the Soyuz was thus redesigned to prevent a recurrence of this unanticipated design flaw. On the other hand, the LES had also worked flawlessly and demonstrated its ability to safely pull cosmonauts from the booster should an emergency arise as it did years later in the Soyuz 7K-ST No.16L abort (26 September 1983).
The emergency condition of the Soyuz 7K-ST No.16L abort was not caused by rotation of the Earth, but by multiple failures that caused damage to the launch vehicle:
> The crew was sitting on the pad awaiting fueling of the Soyuz-U booster to complete prior to liftoff. Approximately 90 seconds before the intended launch, a bad valve caused nitrogen pressurisation gas to enter the RP-1 turbopump of the Blok B strap-on. The pump began spinning up, but with no propellant in it, the speed of rotation quickly exceeded its design limits which caused it to rupture and allow RP-1 to leak out and start a fire which quickly engulfed the base of the launch vehicle. Titov and Strekalov could not see what was happening outside, but they felt unusual vibrations and realized that something was amiss. The launch control team activated the escape system but the control cables had already burned through, and the Soyuz crew could not activate or control the escape system themselves. The backup radio command to fire the LES required 2 independent operators to receive separate commands to do so and each act within 5 seconds, which took several seconds to occur. Then explosive bolts fired to separate the descent module from the service module and the upper launch payload shroud from the lower, the escape system motor fired, dragging the orbital module and descent module, encased within the upper shroud, free of the booster with an acceleration of 14 to 17g (137 to 167 m/s²) for five seconds. According to Titov, "We could feel the booster swaying from side to side. Then there was a sudden vibration and a jerking sensation as the LES activated".
No worries! I wasn’t familiar with these launches offhand myself so your post piqued my curiosity leading me to look the history up myself. And you weren’t far off - if the original launch failure hadn’t occurred, it’s entirely likely that the second launch failure would have been lethal and possibly even more other launches besides that one. Safety and reliability is a moving target but is always worth investing in because it also helps drive costs down and reduces failure modes that may not even be detectable or predictable due to black swan events.
> 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
The problem is that the stabilization system tries to compensate for the rotation of Earth (because it can't make the difference between the rotation of Earth, which shouldn't be compensated for, and the movement of the holder which should be).
So it would work if you were taking a photo of a subject not rotating together with the Earth. Like the stars.
I guess I couldn't quite grok how IBIS would measure the Earth's rotation whilst being on Earth, but as I've now just learned (through various slaps of the forehead) a perfectly vertical spinning gyroscope will definitely tilt with time due to the Earth's rotation and this is measurable to high degrees of precision.
Not just randomly tilt - it will align itself with the poles of a spinning celestial body. It's used in applications that can't rely on correct magnetic variation, like surveying and aircraft inertial navigation systems.
It also does track the revolution of the Earth around the Sun, and that of the Sun around the Milky Way, as well as the various influences over the Milky Way that make it go less than straight on its way towards the Great Attractor.
Those movements just happen to be slow enough that they don't limit image stabilization to 6.3 stops.
The relevant "speed" is the change of the direction you are pointing at. The Earth rotates around itself in 24 hours, but around the Sun in 365 days, so the daily rotation is 365x as fast. We also rotate around the center of the Milky Way every couple of hundreds of millions of years.
At least with respect to the influence of the Earths rotation. With respect to compensating actual camera shake, the modern systems correct 5 axis's. 3 for rotation around the 3 space axis's, and 2 translational, which leaves only motion towards or away from the motive uncorrected for (which usually only expresses itself in the need of refocussing, but that usually is far beyond camera shake, except for macro photography).
Per my other comment: Earth isn't attached to the sun, the sun isn't attached to the galactic center (they are orbiting). They are independent rotational frames of reference. They are also gyroscopes in their own right.
As far as taking pictures of other things on Earth, at least. Taking a picture of another planet/star/galaxy would also face similar challenges.
What's the difference between our "attachment" to Earth compared to Earth's attachment to the Sun? Aren't both doing circular motion due to gravity (in us-Earth's case, gravity + support force from the ground) and inertia?
I never thought of that one. It's fun to think "we know the whole universe isn't spinning very fast, because our gyros are stable". Feels both obvious and somehow bigger-than-life to me.
We are not kinetically bound to the galactic center, there is no friction causing earth to remain "upright" in respect to the galaxy. Earth is also a freely rotating inertial body and, even though wobbly, it is itself a gyroscope.
The next level of stabilization would probably be gravitational waves.
Let's do a small though experiment: Assume you have fixed your camera and the duck on a surface. Then while taking the photo, you rotate the surface. The motion sensor in the camera tries to cancel out this motion, which is suitable for taking a photo of something that's not fixed on the surface, which means it does not work well for the duck that's moving with the camera.
The opposite: Earth rotation is measured by the camera and can't be easily distinguished from camera rotation relative to earth. So image stabilization will also correct for earth rotation, which is undesirable.
