Earth’s Rotation Limiting IBIS Performance to 6.3 Stops ?

archaeopteryx

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David Berryrieser said:
This seems unnecessarily restrictive to me and makes independent verification and analysis of the test impossible.
Agree, though marketing claims like Olympus's 6.5 stops are often intended not to be verifiable in any normal sense. Personally, as someone who's occasionally done measurements which required correcting for the curvature of the earth, I found Olympus's claims pretty weird. It's not especially hard math to correct for gyro precession so the marketing pitch sounded like either trying to sell cameras on the basis of having poor firmware programmers or having management which told the programmers to cripple the system. Either way it looks unintelligent.

Berryrieser's analysis misses a few things.
  • It's not necessary to use GPS to determine latitude since the firmware could just have an option to enter it (no different than the focal length of a manual lens, really). Sure, most people will forget to set it and never change it but it's still less dumb than assuming no rotation. Shipping cameras set to ±45 degrees is an obvious default, would correct reasonably well for most of the Earth's human population, and be better than zero for basically everyone else. Berryrieser's claim the variant he describes would not work without GPS is in the right direction but he misses some trivial solutions, such as continuing with the last known latitude when satellite signals are lost.
  • The claim the camera must be pointed at the subject for an unrealistically long time is potentially true but does not appear to be generally supported. Since the beginning of significant gyro drift is 6.5 stops from the exposure that same amount of time is about what's needed to start up the highpass filter described. For example, 6.5 stops from 1/200 is 400 ms. Even in most quick shooting situations a camera would usually have another second or two to acquire gryo drift information. There's also no requirement drift be calibrated only during subject pointing, meaning potentially the entire uptime of the camera ever can be used. In practice, times where the camera's rotating too quickly would probably need to be excluded but acquiring calibration data whenever the camera's on really shouldn't be problem.
  • The comments mention offset bias noise in gyros exceeding the Earth rotation component but don't complete the thought to using other sensors to define the zero drift point. In this case I'm not familiar with the specific sensors but usually there's some algorithmic iteration between different data sources to get best results. Precession is just another rotation matrix to include there. It does add another degree of freedom and make finding an optimal solution a bit more complex but I'm skeptical of describing it as a barrier.
Since automatic drift cal is the same thing as latitude learning it seems like it would remove need for GPS or latitude entry.
 
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The Grumpy Snapper

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The obvious solution is to buy a brand with IBIS and the option to momentarily stop the Earth's rotation.

Or buy one of the soon to be released gyro stabilised tripods that counteract the Earth's rotation for exposures longer than 4.33 minutes.
 

archaeopteryx

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The obvious solution is to buy a brand with IBIS and the option to momentarily stop the Earth's rotation.
Given enough such cameras the result would be to permanently halt terrestrial rotation. There are some reasons why that's kind of an interesting idea.
 

David Berryrieser

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Berryrieser's analysis misses a few things.
  • It's not necessary to use GPS to determine latitude since the firmware could just have an option to enter it (no different than the focal length of a manual lens, really). Sure, most people will forget to set it and never change it but it's still less dumb than assuming no rotation. Shipping cameras set to ±45 degrees is an obvious default, would correct reasonably well for most of the Earth's human population, and be better than zero for basically everyone else. Berryrieser's claim the variant he describes would not work without GPS is in the right direction but he misses some trivial solutions, such as continuing with the last known latitude when satellite signals are lost.
  • The claim the camera must be pointed at the subject for an unrealistically long time is potentially true but does not appear to be generally supported. Since the beginning of significant gyro drift is 6.5 stops from the exposure that same amount of time is about what's needed to start up the highpass filter described. For example, 6.5 stops from 1/200 is 400 ms. Even in most quick shooting situations a camera would usually have another second or two to acquire gryo drift information. There's also no requirement drift be calibrated only during subject pointing, meaning potentially the entire uptime of the camera ever can be used. In practice, times where the camera's rotating too quickly would probably need to be excluded but acquiring calibration data whenever the camera's on really shouldn't be problem.
  • The comments mention offset bias noise in gyros exceeding the Earth rotation component but don't complete the thought to using other sensors to define the zero drift point. In this case I'm not familiar with the specific sensors but usually there's some algorithmic iteration between different data sources to get best results. Precession is just another rotation matrix to include there. It does add another degree of freedom and make finding an optimal solution a bit more complex but I'm skeptical of describing it as a barrier.
Since automatic drift cal is the same thing as latitude learning it seems like it would remove need for GPS or latitude entry.
With regards to using GPS, yes, you are of course correct. You could have the user set the latitude, use the last known GPS, and the system would work most of the time. But if you get on a plane, land in a new place, and start shooting, your camera could be trying to correct for the wrong drift and mess the image up more than if we had no Earth rotation compensation. In this case I think the engineers would play it safe to avoid the risk of messing up some pro's shoot.

With regards to drift, you can't acquire drift information while handholding. The slow drift in your pointing will be greater than Earth's rotation rate. If you try to zero out the drift in this time, you are just going to be erroneously cancelling the drift rate from your hands which is going to be completely different a couple seconds later. For the is to work, you must be able be able to hold the camera steady with a DC drift rate of less than 0.004 degrees/sec (Earth's rotation rate). You could of course hold it steady for longer to integrate, but it would have to be long enough to make Earth's rotation large compared to your personal drift rate. I could probably hold a camera pointed at the subject to with a couple degrees over time. That would still require minutes of holding steady before the shot to effective measure and cancel Earth's rotation rate.

In order to calibrate away drift, the camera must be held steady. Preferably resting on a solid surface. This could measure and cancel Earth's rotation fairly quickly, but you can't set and forget. If you turn around 180 degrees, the effect from Earth's rotation will be in the opposite direction. You could of course have the gyro try to measure the camera's position at all times to do proper inertial sensing, but this would require your gyro to be running at all times, draining the battery. You might be able to pull in a magnetometer to help with orientation, but this is subject to its own pitfalls, particularly since the camera body is made of metal and does some shielding. Anyways, I certainly don't think it is impossible to compensate for Earth's rotation and is quite easy to do in a lab. It's just hard on a consumer camera.
 

The Grumpy Snapper

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Given enough such cameras the result would be to permanently halt terrestrial rotation. There are some reasons why that's kind of an interesting idea.
That's why there's only a handful in circulation, all in the hands of Nat Geo photographer's. They're not allowed to have more than two on the same continent at any one time.
 

archaeopteryx

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your camera could be trying to correct for the wrong drift
Hi David, yes, it could. But unwinding integrators to handle such cases is a well known thing in control system design. The most common methods are probably simple reset to default and adaptive relaxation of integrator bandwidth. You're correct that if the control loop is too dumb to dump state and it can do worse than no compensation but the latitude exchanges required to hit that case are unlikely. In a dumb system the error would still only apply for the time required to retrain the integrator. In such a case problems could be provoked by choosing an integrator bandwidth in the single digit mHz range or below but, even then, they wouldn't be noticeable to most users most of the time. So there is some difficulty to arguing the behavior would make the system create more problems than it reduces.

you are just going to be erroneously cancelling the drift rate from your hands which is going to be completely different a couple seconds later
Sure, it's an error with respect to just the terrestrial rotation component. But what you're describing as incorrect is the intended design behavior since compensating such motion the system's task. It may be helpful to develop an error budget based on some PID simulations.

If you turn around 180 degrees, the effect from Earth's rotation will be in the opposite direction.
In my experience, accelerometers commonly track orientation through considerably more complex motions with little difficulty. Something I suspect was overlooked, and which probably creates more engineering difficulty, is orientation is unknown at power on. I'd suggest focusing on this aspect---particularly for the common use case of turning a camera on, promptly capturing one image, and turning it off again---in preference to comparatively uncommon long distance, north-south aircraft travel. One possibility, which strikes me as reasonably likely, is the maximum amount of stabilization may increase over time. As you've pointed out, however, this isn't an especially simple thing to test.

particularly since the camera body is made of metal
Magnesium is kind of viewed as straddling the diamagetic-paramagnetic distinction. So this assumption would likely benefit from an analysis including the other interference sources. That may take some time.
 
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I've read some of this and respectfully ask is this an April fools joke gone feral?
I've a total station (modern theodolite that reads distance) that has compensators to cater for slight movement, keep it level etc
Vibrator rollers play Larrydoo with the device, understandably.
But I've never seen any mention of earth's rotation, and other terrestrial interference other than pure atmospherics in distance corrections and the usual optical aberrations any lens suffers from.
I have Nikon ED glass in the lens.
I'm sure we would have been informed if such is an issue.
Reading accurate angles is far more important than simply stopping the jitter in holding my camera steady.

I've a very open mind on this but also a questioning one.
 

Bushboy

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And the dday clock is now, 100seconds to midnight, exactly because of disinformation like this....
 

archaeopteryx

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is this an April fools joke gone feral?
I like that phrase and kind of wish it could be applied to more marketing. Since a total station lacks a gyroscope it's hard for it to be subject to Coriolis precession. So if you'd like to reason by analogy, it'd be more effective to pick something with two correlated, rotating frames of reference. (Similar error sources do exist within a single spinning frame of reference but they're negligible even for long term GNSS-RTK base stations. If you're curious anyway and have paywall access, try Ignazio Cuifolini.)
 
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Mack

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Their E-M1X ad claims 7 stops of stabilization. Wonder if they do it along with using its internal GPS for the latitude correction that the E-M1 Mark II with 6.5 stops of stab. does not have?
 
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I like that phrase and kind of wish it could be applied to more marketing. Since a total station lacks a gyroscope it's hard for it to be subject to Coriolis precession. So if you'd like to reason by analogy, it'd be more effective to pick something with two correlated, rotating frames of reference. (Similar error sources do exist within a single spinning frame of reference but they're negligible even for long term GNSS-RTK base stations. If you're curious anyway and have paywall access, try Ignazio Cuifolini.)
That's way over the top for my level of understanding and use.
We have gyroscope theodolites that don't rely on GPS, work above and deep below ground and are quoted accuracy of angle measurement of 1.2 to 1.6 cm over 1 km.
12mm in 1000 metres wouldn't necessarily I imagine worry a lens, unless resolution power is phenomenal.
I don't know but can a telephoto split say a 12mm, ½" dowel at 1000 metres?
That's 1.2mm at 100 metres.
Refraction, diffraction and aberrations from the atmosphere would wipe that I imagine.
I'm just trying to think practically on this.
Some of the information in those links is terrestrial (Mars 299 million km away) and distances such that a whisker of a second of arc would miss the mark.
Maybe I've missed something in all this?
 

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