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Earth rotation limits in-body image stabilization to 6.3 stops (2020)

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Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#61
post #3

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?

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 gyrosc…

I think you’re mixing up different launches: Soyuz 7K-OK No.1 and Soyuz 7K-ST No.16L

Soyuz 7K-OK No.1 was uncrewed and likely had the quirk with the gyros. One person near the launch on the ground was killed.

https://en.wikipedia.org/wiki/Soyuz_7K-OK_No.1

> 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:

https://en.wikipedia.org/wiki/Soyuz_7K-ST_No.16L

> 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".

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#62
post #46

Earlier quoted context omitted.

I believe that fancy astrophotography tripods already do that rotation for you, right? I think that for astrophotography, the shutter times are so long that you have to build it into the tripod, instead of relying on the tiny amount of stabilization that can be done in-camera. Although maybe it would be helpful to cancel out some motor noise of vibrations from the tripod. But probably the existing image stabilization…

Pentax cameras take a different approach with stabilization--rather than stabilize inside lens, which means every lens is shipping its own stabilization solution, they stabilize the sensor itself. It limits stabilization to two axes, but now any lens is essentially stabilized. And it also lets them do some tricks, since it's so integrated. One is to do sub-pixel sensor shifts for higher res photos, and another is to…

This is also how any IS lenses for film cameras work since moving the film around isn't entirely practical.

Nikon: https://www.nikonusa.com/learn-and-explore/c/products-and-in...

You can see the VR lens element there.

The Canon version: https://www.canon-europe.com/pro/infobank/image-stabilisatio...

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#63
post #21

You don't need GPS to figure out the correction for this. Inertial navigation systems in aircraft (which use very stabilised platforms with a lot of math involved) worked before GPS was available. It helps to have a rough indication of the current latitude on startup, but you can also figure it out from the gyro outputs. Just takes longer. With modern sensors (solid state laser gyroscopes) it has all become a lot sma…

I mean, surely if you are doing something that requires this level of precision, you could just ask the user to input its current known location? I doubt that even if the user misdialed by ten or twenty meters the difference in compensation would matter (or even if the camera was actually moving around).

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#64
post #23

Earlier quoted context omitted.

Why does it stop at Earth's rotation? What about revolution around the Sun?

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.

I still don't quite get it.

Under what definition the Earth's revolution is "slower" than its rotation?

Why can the camera's stabilization system detect the rotation and correct it (and causes undesirable result) but not the revolution?

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#65
post #29

Earlier quoted context omitted.

Why does it stop at Earth's rotation? What about revolution around the Sun?

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?

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#66
post #23

Earlier quoted context omitted.

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.

I still don't quite get it. Under what definition the Earth's revolution is "slower" than its rotation? Why can the camera's stabilization system detect the rotation and correct it (and causes undesirable result) but not the revolution?

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.

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#67
post #45
post #43

Can somebody ELI5 this to me? The image with the 2 earths.. that only works if the camera is not also on the ground, but it is? How is the rotation of the object and the camera not identical? Why would it rotate ‘upwards’? Also, if the issue is relative motion or rotation between camera and object, wouldn’t two sensors, one on the camera and one on the subject be able to solve this, since we can see if their rotation…

Imagine the camera were floating just above the surface of the Earth, and also that it had perfect image stabilization. This image stabilization would keep the camera always oriented in the same direction. Same direction relative to what? To the rest of the universe. So if it was pointing right at a star, it would continue pointing directly at that star as it went around and around the Earth. From our perspective on…

> Same direction relative to what? To the rest of the universe

By this logic, the Earth's revolution would also cause similar issue, and even worse. But in reality only the rotation does.

I think at least some part of your explanation does not calculate.

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#68
post #46
post #36

On the other hand, that should be awesome for astrophotography.

I believe that fancy astrophotography tripods already do that rotation for you, right? I think that for astrophotography, the shutter times are so long that you have to build it into the tripod, instead of relying on the tiny amount of stabilization that can be done in-camera. Although maybe it would be helpful to cancel out some motor noise of vibrations from the tripod. But probably the existing image stabilization…

> I believe that fancy astrophotography tripods already do that rotation for you, right?

There are various types of mounts, and each type can be either basic or fancy. The specific type of mount that deals with rotation of the sky (around the north/south stars):

* https://en.wikipedia.org/wiki/Equatorial_mount

You can can get non-fancy ones (US$ 240):

* https://optcorp.com/collections/equatorial-mounts/products/o...

Or fancy ones ($20K):

* https://optcorp.com/collections/equatorial-mounts/products/a...

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#69
post #66

Earlier quoted context omitted.

I still don't quite get it. Under what definition the Earth's revolution is "slower" than its rotation? Why can the camera's stabilization system detect the rotation and correct it (and causes undesirable result) but not the revolution?

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.

Ah, so the angle (orientation?) is what actually matters? It makes sense now.

Thanks!

Re: Earth rotation limits in-body image stabilization to 6.3 stops (2020)

#70
Version 2 sounds to me as the probably reason for the ability of Cameras like the OM1-2 to go over 8 stops. Yes, it is probably not a simple task to measure the earths drift with the gyroscopes, but there is one thing that might help: the frequency of that drift is exactly known - it is the speed of the earths rotation. So it should be possible to tune a very narrow filter to that frequency and only analyze the gyroscope signal for that frequency. With that one could at least partially compensate for the drift.
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