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01-07-2020, 02:12 AM   #46
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QuoteOriginally posted by stevebrot Quote
Moment of inertia...subtle, but real.
Moment of inertia, without acceleration doesn't affect sharpness.

---------- Post added 07-01-20 at 10:17 ----------

QuoteOriginally posted by photoptimist Quote
f you attempt to rotate a spinning gyroscope, it exerts a directional force that can be measured and used to estimate the axis and rate of the imposed rotation. The gyro sensors in the camera can't hold the camera still but they can provide data to tells the SR system which way to pan or rotate the sensor to correct for the measured rotation of the camera body.The camera direction really does matter alot when it comes to how the Earth's rotation affects the motion of the image.For someone in the Northern hemisphere, pointing the camera due East, the gyro sensor will tell the SR system to pan upwards and to the right at an angle from the zenith related to the latitude and time of year.For someone in the Northern hemisphere, pointing the camera due West, the gyro sensor will tell the SR system to pan downwards and to the left at an angle from the nadir related to the latitude and time of year.If the shooter does not wait for a GPS lock, the camera does not know that it is in the Northern hemisphere or its latitude. If the shooter does not recalibrate the compass often enough, the camera can't be sure whether it is pointing East or West (or North or South).If the shooter did always wait for a GPS lock and did always carefully recalibrate the compass, then that information could be used to subtract the known spin of the Earth from the measured spin of the camera to avoid a star-trail effect on Earth-bound scenery.
If image sharpness is only affected by change of sensor position during exposure, and the SR servo only correct for changes acting as low pass filter (dx/dt, dy/dt), then why would earth rotation (constant speed, zero acceleration) have any effect on SR performance?


Last edited by biz-engineer; 01-07-2020 at 02:18 AM.
01-07-2020, 07:18 AM   #47
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QuoteOriginally posted by biz-engineer Quote
Moment of inertia, without acceleration doesn't affect sharpness.

---------- Post added 07-01-20 at 10:17 ----------



If image sharpness is only affected by change of sensor position during exposure, and the SR servo only correct for changes acting as low pass filter (dx/dt, dy/dt), then why would earth rotation (constant speed, zero acceleration) have any effect on SR performance?
The core issue is that the SR system tracks camera motion with respect an Inertial frame of reference, not with respect to the Earth's rotating frame of reference.

Current gyro sensors are sensitive enough to easily detect and measure that an Earth-bound camera is rotating about 15° per hour and will attempt to remove the effects of that Earth rotation from the image. The problem is that the SR system has no easy way of knowing* that the subject matter is also rotating with the camera by 15° per hour. Thus, the SR system ends up adding a 15° per hour blur to the image.

*In theory, the SR system could subtract the 15° per hour Earth rotation signal from the gyro sensor data. But in practice, that requires waiting for GPS lock before the shot and having a 3 D magnetic field meter that is calibrated for current the lens on the camera and the current location.
01-07-2020, 07:22 AM   #48
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QuoteOriginally posted by stevebrot Quote
Only on week-ends.
Sacrilege what about public holidays

---------- Post added 01-08-2020 at 01:23 AM ----------

QuoteOriginally posted by ismaelg Quote
Wait! Isn't the Earth flat?
Doesn't stop the rotations

---------- Post added 01-08-2020 at 01:34 AM ----------

QuoteOriginally posted by photoptimist Quote
Shaky people might seem much better
The original pixel shift

---------- Post added 01-08-2020 at 01:38 AM ----------

On a serious note thank you Photoptimist it is amazing what is built into these cameras and why
01-07-2020, 08:48 AM - 1 Like   #49
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QuoteOriginally posted by biz-engineer Quote
I don't understand, we all spin at the same speed on the surface of earth, the camera spins at the same speed as its owner and the subject in front of the lens, if that wasn't the case we'd be in big trouble.
While i don't think this is the reason for the limitation (see photoptimist's explanation on the first page of the thread), the speed at which you're moving depends on how far you are from the Earth's centre, ie how high up you are. You're moving faster at the top of Everest than standing at sea level on a street in the Netherlands.

01-07-2020, 09:01 AM   #50
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The post is from Sep 26, 2016...
01-07-2020, 09:56 AM   #51
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QuoteOriginally posted by biz-engineer Quote
Moment of inertia, without acceleration doesn't affect sharpness.
By Jove! I think he's got it!


Steve

(...acceleration being a component of shake...)
01-07-2020, 09:58 AM   #52
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QuoteOriginally posted by James also Quote
Doesn't stop the rotations
Yes...it rotates in the manner of a vinyl record on a platter.


Steve

01-07-2020, 10:35 AM   #53
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QuoteOriginally posted by photoptimist Quote
It's actually because the MEMS gyros are so good that this is a problem. The modern chips are now accurate down to almost 1 degree per hour so they readily sense the 15° per hour rotation of the Earth and camera.

If you put the camera on a solid tripod and read the signal from the gyro, the gyro would tell you that the camera is actually spinning once per day about an axis pointed at the North Star. And if the camera's software knew it was on a perfectly solid tripod (which don't exist in real life), the software could easily know to ignore the measurable spin of the Earth, camera, and subject.

But, in real life, the data from the gyros of a handheld camera would show all sorts of random rotations in random axis directions. Unless the camera can be confident about whether it is pointing North, East, South, or West, it doesn't know how to subtract the Earth's rotation from the gyro data to accurately estimate the rotation of the camera relative to the Earth.

The limitation is actually the flip-side of the astrophotographer's problem with star trails. On a K-1 with a 100 mm lens fixed on a tripod, the Earth's rotation means the stars move as much as 1 pixel every 1.5 seconds (depending on the pointing direction). Using the raw gyro signal for motion correction can remove the Earth's rotation but now all the Earthly subjects in the scene start moving up to 1 pixel every 1.5 seconds. That implies that shutter speeds slower than 150/F will show Earth rotation effects at the pixel peeping level. That's 7.2 stops slower than the 1/F rule of thumb for safe shutter speeds.
I had thought that in-lens stabilization was done wih gyros - is Pentax's IBIS also affected in the same way? So far, the stability I learned to provide 50 years ago hand-holding a camera continues, so this is a theoretical thing for me. but I know my body will fail me someday .......
01-07-2020, 10:50 AM - 2 Likes   #54
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I practice my inner chicken to stabilize.
01-07-2020, 12:42 PM   #55
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QuoteOriginally posted by reh321 Quote
I had thought that in-lens stabilization was done wih gyros - is Pentax's IBIS also affected in the same way? So far, the stability I learned to provide 50 years ago hand-holding a camera continues, so this is a theoretical thing for me. but I know my body will fail me someday .......
I think the earliest ones did but every more recent in-lens stabilizer I've ever dug into uses gyro sensors, a computer, and electromagnets to shift a lens group in X & Y.

And, yes, Pentax IBIS is affected by this, too. It's caused by living on a silly spinning planet.

If you could handhold a 100mm lens shot for more than 1.5 seconds, you too would suffer from this. Your ear's semi-circular canals would feel the spin of the Earth and make you think you need to adjust the camera's pointing direction by 15° per hour.

Personally, I love image stabilization for shooting in dark places (e.g., cathedrals & museums) where tripods and flash are usually forbidden. And it comes in handy at dawn, dusk, and night. It's great for full-moon night hikes.

Last edited by photoptimist; 01-07-2020 at 01:56 PM.
01-07-2020, 01:35 PM   #56
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QuoteOriginally posted by stevebrot Quote
Yes...it rotates in the manner of a vinyl record on a platter.
EUREKA! Of course, that explains everything! I well remember the manner in which vinyl LPs waved up and down, rotating on my turntable: would you believe some weirdos told me the turntable was warped, not the discs themselves. I long ago concluded it was the effect of too much sunlight; but they hotly denied this, insisting they rarely left their homes outwith the hours of darkness. Clever chaps, the Olympus engineers.


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01-07-2020, 05:08 PM   #57
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QuoteOriginally posted by StiffLegged Quote
Clever chaps, the Olympus engineers.
Of course, that was in 2016. They may not be as clever now.


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01-07-2020, 07:12 PM   #58
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QuoteOriginally posted by StiffLegged Quote
EUREKA! Of course, that explains everything! I well remember the manner in which vinyl LPs waved up and down, rotating on my turntable: would you believe some weirdos told me the turntable was warped, not the discs themselves. I long ago concluded it was the effect of too much sunlight; but they hotly denied this, insisting they rarely left their homes outwith the hours of darkness. Clever chaps, the Olympus engineers.


We learn something new every day!
Damn if it is us that are turning then we are not floating through space on top of four elephants who are standing on the great Turtle A'tuin
01-07-2020, 07:47 PM   #59
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QuoteOriginally posted by James also Quote
Damn if it is us that are turning then we are not floating through space on top of four elephants who are standing on the great Turtle A'tuin
Too bad. Bet we could get beyond 6.5 stops then.
01-08-2020, 12:45 AM   #60
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QuoteOriginally posted by fs999 Quote
The post is from Sep 26, 2016...
Means it's not valid in 2020 because earth rotation has changed?
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