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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)

#81

Post by trhway »

eggy wrote: post #59

Well, if we're nitpicking here, it is not 86,000s/day (24 hours * 3600s/hour) and 7.27x10^-5 radians/s, but 86,164.091s and 7.29x10^-5 radians/s. 24 hours is the time it takes the sun to return to the same spot in the sky due to earth having to rotate for another 3m56s to make up for angle gained by revolving around the sun in the same direction as the rotation of the Earth. This applies for the other planets that al…

>Damn, I knew that is why I botched my 6-stop exposure at my daughter's graduation!

how about driving for 6-stop before taking the shot a tank with stabilized gun trained to the target. Now the tank gunner has the excuse too.

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

#82

Post by SassyBird »

siriaan wrote: post #38
nimbleal wrote: post #18

Earlier quoted context omitted.

Yes, or considered another way 1/25th shutter vs almost 1/2000th, ie a lot of motion blur vs. virtually nothing will be able to provoke blurring

Except a moving subject, of course.

At 1/2000th both a running cheetah and a running squirrel are completely frozen. I haven’t yet found anything that isn’t frozen with that setting. I suspect at that point you’re in the domain of bullets, very outstretched springs and the like.

Edit: yeah, a speeding bullet caught at 1/5000th: https://flickr.com/photos/hoohaaphotos/5587502201/>

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

#83

Post by dakr »

GuB-42 wrote: post #36

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

The issue is rotation of the sky about the line of sight axis. Whether the exposures are short or long, over time the sky will rotate more than what an in-camera system can compensate for (the amount of rotation depends on location/time/direction). Over these timescales a rotator that can perform larger movements is needed. This can be provided by an equatorial mount or an internal rotator.

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

#84

Post by jerich »

Euphorbium wrote: post #22
blueflow wrote: post #20

Earlier quoted context omitted.

It doesn't.

Eventually we will have to compensate for gallactic rotation.

Anyone who’s read the short story “The Billiard Ball” by Asimov would have taken it into account.

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

#85

Post by chris_va »

Solution (2) as written seems to imply that the camera can only use the gyroscope signal while the camera is pointed at the subject, but I cannot see why that is a strong limitation.

In theory, you can take the last N seconds of data from the gyroscope (I assume it is running while the camera is active) to get the overall drift, even if it is tumbling around for a while before being pointed at the subject... Assuming the tumbling has enough periods of time that are correlated with the earth's rotation (e.g. someone carrying it, not pointing it an an aircraft or something moving EW for the window duration that is anticorrelated with the rotation).

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

#86

Post by exitb »

moi2388 wrote: 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…

https://youtu.be/1zJ9FnQXmJI

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

#87

Post by tonyarkles »

labcomputer wrote: post #57
Rinzler89 wrote: post #35

Earlier quoted context omitted.

> Inertial navigation systems in aircraft (which use very stabilised platforms with a lot of math involved) worked before GPS was available. Inertial measurement units for aircrafts and submarines cost as much as a house in California. Good luck putting those in a phone.

Well, that, and there's no such thing as a "solid state laser gyro". I believe the GP is confusing MEMS solid-state gyros and laser-ring gyros (which can use a solid state laser, but AFAIK aren't ever called "solid state laser gyro"). MEMS gyros have too much bias drift (both on a unit basis due to fab processes and on a temperature basis) to be practically useful here. You can measure the earth's rotation with a MEM…

Heh, while I get what you're saying... despite being somewhat pedantic... there are in fact MEMS FOGs now too :). https://www.anellophotonics.com/technology

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

#88

Post by Filligree »

Karellen wrote: post #79
Filligree wrote: post #71

Earlier quoted context omitted.

The Earth's revolution around the sun? What makes you think it doesn't? It's just that the effect is 1/365 the size, on the same axis as the rotation.

The same axis of rotation? Pretty sure they're about 23° off.

Alright, close-ish to the same axis.

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

#89

Post by akira2501 »

t0mas88 wrote: 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…

> worked before GPS was available.

Worked makes it seem like you throw a switch and it just gives you position data. Those units take anywhere from 6 to 10 minutes to align, if you move the platform, it will error out and you must restart the alignment. The current systems take their initial fix from GPS, but the initial systems, the operator had to manually know and then key that information into the unit.

"Worked" with extreme care operated by a qualified professional.

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

#90

Post by legulere »

zamalek wrote: post #25
tetris11 wrote: 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?

In terms of flatland: 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 9…

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.

https://en.wikipedia.org/wiki/Inertial_frame_of_reference

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