[HN Gopher] Earth rotation limits in-body image stabilization to...
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Earth rotation limits in-body image stabilization to 6.3 stops
(2020)
Author : pwnna
Score : 137 points
Date : 2024-05-16 03:17 UTC (19 hours ago)
(HTM) web link (thecentercolumn.com)
(TXT) w3m dump (thecentercolumn.com)
| kqr wrote:
| 6.3 stops is a lot, though. That's basically the fully usable
| aperture range of a kit zoom lens.
| nimbleal wrote:
| 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
| siriaan wrote:
| Except a moving subject, of course.
| SassyBird wrote:
| 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/>
| dale_glass wrote:
| Stabilization doesn't help with subject movement, it only
| helps with the camera's shake.
|
| So with this level of stabilization, you'll take a
| picture of a running cheetah at 1/25 as if it were 1/2000
| only as far as the stability of the camera is concerned.
| So if you're not tracking the cheetah you'll get a sharp
| background because the shaking of your hands has been
| nullified, but the cheetah is still moving within the
| frame and still blurry.
| noselasd wrote:
| What are these "stops" in this context, for the non-photo nerds
| ?
| poulpy123 wrote:
| it's an abstraction of the aperture size and exposition time.
| If you expose twice as long it gives the same light than an
| aperture twice the surface. Those 2 are discrete in camera,
| so it is abstracted as stops. Exposure time is limited by
| movement, and aperture size is limited by the optics itself.
| Sensor stabilization allows to gain "stops" by extending the
| exposition time before the image becoming blurry from the
| photographer movement, thus allowing as much more light to
| come
| formerly_proven wrote:
| A stop generally is a doubling/halving of light intensity at
| the sensor. For apertures this means a factor of sqrt(2) on
| the diameter (because the area is what matters), for exposure
| times a doubling/halving of the time.
|
| "Stops of stabilization" in this specific context refers to a
| standardized CIPA test which determines a shutter speed where
| the image remains acceptably sharp. They then calculate the
| number of stops to 1/focal-length, which is a rule of thumb
| for getting sharp images from the 1950s. So if a 200mm lens
| produced a sharp image at 1/10s in the CIPA test, then that
| would be 1/10 -> 1/20 -> 1/40 -> 1/80 -> 1/160 -> 1/200 about
| 4.3 "stops of stabilization".
|
| The results from the CIPA test don't really hold up to the
| real world though once you move beyond ~4 stops.
| vouaobrasil wrote:
| However, it's not the aperture range that matters.
| Theoretically, if earth were not rotating, then 10 stops would
| still be useful for long-exposure photography. In other words,
| the stop differences in stabilization are more useful when you
| think of then in terms of shutter speed, NOT aperture.
| tetris11 wrote:
| 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?
| aljgz wrote:
| 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.
| seszett wrote:
| It's explained here:
|
| > _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.
| tetris11 wrote:
| 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.
| anilakar wrote:
| 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.
| thrdbndndn wrote:
| Why does it stop at Earth's rotation? What about revolution
| around the Sun?
| blueflow wrote:
| It doesn't.
| Euphorbium wrote:
| Eventually we will have to compensate for gallactic
| rotation.
| viraptor wrote:
| 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.
| zamalek wrote:
| 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.
| jerich wrote:
| Anyone who's read the short story "The Billiard Ball" by
| Asimov would have taken it into account.
| seszett wrote:
| 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.
| thrdbndndn wrote:
| 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?
| _ph_ wrote:
| 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.
| thrdbndndn wrote:
| Ah, so the angle (orientation?) is what actually matters?
| It makes sense now.
|
| Thanks!
| _ph_ wrote:
| 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).
| zamalek wrote:
| 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.
| thrdbndndn wrote:
| 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?
| zamalek wrote:
| The Earth is in freefall above the sun. We are not in
| freefall. https://en.wikipedia.org/wiki/Free_fall
| lolc wrote:
| 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.
| yetihehe wrote:
| 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.
| Gravityloss wrote:
| 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.
| aspenmayer wrote:
| 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 8deg 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".
| zamalek wrote:
| 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 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.
| legulere wrote:
| 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
| contravariant wrote:
| Well if it keeps pointing in the exact same direction then it
| would stay fixed on whatever star it is currently pointing
| towards.
|
| Which is normally not a problem, but relative to something on
| the surface of the Earth the stars do move.
|
| So I guess you should ask people to stand directly in front of
| Polaris if at all possible.
| quonn wrote:
| Would it be possible to correct for the rotation by counter
| rotating if the orientation of the camera is known (or determined
| by GPS + compass)?
| isoprophlex wrote:
| > The second solution is much more plausible, but still very
| difficult. The user would have to be pointing the camera at the
| subject for long enough such that the drift in their aim at the
| subject is smaller than the drift from the rotation of the earth.
| This is also implausible. What is concerning though, is that this
| second method is one that could work very well to cancel out
| Earth's rotation on the CIPA specified stabilization test
| apparatus.
|
| So, basically dieselgate but for image stabilization
| nick7376182 wrote:
| It seems the camera could use optical flow to get a baseline
| reading and calibrate the inertial frame offsets. They don't
| need to point accurately for a long time?
|
| Or maybe that is the method they assume for the second solution
| and they calculated that it's infeasible.
| DoctorOetker wrote:
| This can be fixed in software:
|
| you can back calculate orientations with high pass filterd gyro
| data, to rotate the unfiltered gyro date into the current
| reference frame, then low pass the unfiltered but rotation
| corrected gyro data to get the earth rotation axis in the current
| reference frame, then one can estimate the expected rotation that
| should be ignored.
| t0mas88 wrote:
| 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 smaller so if you really want to you can do this in
| a camera. It's just probably going to be too expensive for what
| it brings, because 6+ stops of stabilisation is a lot already.
| crubier wrote:
| Aerospace grade laser gyroscopes are incredibly expensive (and
| bulky), and even then, they still have massive drift after
| several hours. If you don't have GPS to relocalize precisely at
| least every day, there is no way you can know the location of
| the camera on earth for more than a day, even with state of the
| art aerospace stuff
| TaylorAlexander wrote:
| Realistically GPS is the answer, but it's notable that you
| could also use a simple light sensor combined with accurate
| clocks to get your position on earth:
|
| https://en.m.wikipedia.org/wiki/Light_level_geolocator
| vmfunction wrote:
| > Recording light levels over time Wonder how much time is
| needed to determine location.
| TaylorAlexander wrote:
| You just need to determine the time of sunrise and sunset
| relative to a known location and you get a rough idea of
| latitude and longitude.
| labcomputer wrote:
| > they still have massive drift after several hours. If you
| don't have GPS to relocalize precisely at least every day
|
| I think you may be confusing two concepts: Measurement of
| true north and latitude via gyro (what the GP is talking
| about) and inertial navigation systems (which, yes, do
| drift).
|
| You can measure those two things with just a single-axis gyro
| and no external references using a technique called "gyro-
| compassing". In fact, most internal navigation systems use
| gyro-compassing to directly measure true north and latitude
| to align the system on initial startup.
| t0mas88 wrote:
| But the location of the camera doesn't matter. You only need
| to figure out very roughly at which latitude you are to know
| by how much to compensate for earth rotation. And you can do
| that with the sensors that you're already using to do the
| stabilisation. That was my point... no need for GPS.
| throw0101c wrote:
| > _You don 't need GPS to figure out the correction for this._
|
| Perhaps not, but a lot of cameras already have it for
| geotagging purposes (EXIF), so why not use it:
|
| *
| https://en.wikipedia.org/wiki/List_of_cameras_which_provide_...
|
| * https://www.digitalcameraworld.com/buying-guides/best-
| camera...
| Rinzler89 wrote:
| _> 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.
| ben_w wrote:
| The IMUs that existed on aircraft _before the invention of
| GPS_ have been superseded by the ones which actually are in
| your phone, in much the same way and for much the same reason
| that a $20 Casio F-91w keeps better time than a fancy Rolex
| that costs more than a house in California: electronics are
| cheaper and better than mechanical systems.
|
| We have, naturally, _also_ made better IMUs for places where
| it matters, ones which won 't fit in your phone.
|
| The question is therefore not suited to "aircraft grade, yes
| or no?", it's "how expensive is the cheapest IMU that's good
| enough for the specific need?" which in this case itself
| depends on how many stops is desired.
| wkat4242 wrote:
| Actually that F91W does not keep very good time.
|
| There pretty excellent if you keep them on a shelf bit if
| you run around outside in the hot and cold (you know, like
| people use a watch) they'll deviate quickly. Because they
| don't have a temperature controlled (or even compensated)
| oscillator. A real TXCO (basically putting the crystal
| inside a temp calibrated oven) is not feasible on a watch
| battery but compensation sure would be.
| ben_w wrote:
| I picked it not because it's good, but to illustrate the
| cheapest digital is still better than any analog
| mechanism that money can buy.
| labcomputer wrote:
| 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 MEMS gyro, but you're really at the limit.
| jjk166 wrote:
| Laser ring gyros are referred to as solid state laser
| gyros.
| tonyarkles wrote:
| 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
| svalorzen wrote:
| 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).
| akira2501 wrote:
| > 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.
| Asraelite wrote:
| > The first isn't a good solution for many reasons. Don't have
| GPS signal? Shooting next to a magnet? Your system won't work.
|
| These seem trivial to work around. Just store the last known
| position and use that. It's rare that you'll be without a GPS
| signal or beside a magnet, and you certainly won't be traveling
| long distances in those conditions. And since when do magnets
| block GPS signals?
| sokoloff wrote:
| It's not that a magnet blocks GPS signals, but it does affect
| the compass in the context of using 6 of the 9 degrees of
| freedom in the first proposed solution: "Use the camera's GPS,
| accelerometer, and compass to calculate exactly where it is
| pointed and its latitude. " (This solution should also do
| sensor fusion with the gyroscope, not just accelerometer and
| compass for orientation from a 9DoF system.)
| GuB-42 wrote:
| On the other hand, that should be awesome for astrophotography.
| SamBam wrote:
| 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 already does this.
| matthew-wegner wrote:
| 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 do
| astrophotography tracking when GPS data is available.
|
| Much more limited in scope than a full tracking gimbal, but
| not bad considering it's built into the camera (earlier
| bodies had a GPS attachment that slotted into the hot shoe
| connector): https://www.lonelyspeck.com/pentax-k-1-mark-ii-
| astrophotogra...
| Espressosaurus wrote:
| Most cameras these days--other than the low end and the
| very high end--have IBIS (In-Body Image Stabilization)
| built in, and then stabilization built into the longer
| lenses (typically > 100mm). In higher-end/more recent
| cameras that both IBIS and lens stabilization can work
| together to improve how effectively the system works. I
| don't know if it's true of universally, but the recent
| cameras in Nikon's ecosystem which I'm familiar with use a
| 5-axis IBIS unit. A quick search suggests the K-1ii and
| some other Pentax cameras also moved to 5-axis IBIS--
| probably one of the reasons most brands are claiming 5+
| stops in-body these days.
|
| OM-1, formerly Olympus, does has some very cool tricks
| using the tiny micro 4/3s sensor combined with a sick IBIS
| unit allowing hand-held astrophotography that the larger
| companies haven't bothered with.
| shagie wrote:
| 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...
| Espressosaurus wrote:
| Fancy astrophotography tripods--really, the mount--do that
| rotation for you. That's why they exist. Even fancier ones
| exist that permit close-to-arbitrary slewing. Those can be
| used as a go-to-mount where with the right software, it can
| image wherever in the sky you're pointed, take the current
| time, and plate solve for where it's pointed, then finally
| point at whatever target you actually want to shoot.
|
| For the very long exposure times, you can also hook a second
| camera up and run closed loop control on a specific star to
| keep your primary image sensor trained on the correct target
| to even tighter tolerances. There's companies making cameras
| that combine both the primary and secondary camera into a
| single housing so you don't need to fit a second camera +
| lens to your setup, or insert a prism to pick off part of the
| image to go to a second camera.
|
| Amateur astrophotography today does tricks you needed access
| to a dedicated lab to do in previous decades. It's amazing!
| throw0101d wrote:
| > _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...
| dakr wrote:
| 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.
| bongodongobob wrote:
| It has no bearing. Tracking is how you keep stars from
| smearing, not stabilization.
| moi2388 wrote:
| 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
| rotations/movement match up or not?
| SamBam wrote:
| 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 the surface, the
| camera would appear to be flipping over itself as it kept
| pointing at that star.
|
| Unfortunately, this would be pretty bad for taking a picture of
| something that was right in front of the camera (relative to
| the surface of the Earth). You'd be in front of the camera,
| ready for your picture, and the camera would appear start
| rotating as it kept that distant star in view.
|
| So with a perfect image stabilizer, this is what the camera is
| actually trying to do, even when standing on the Earth with a
| tripod. It actually senses the rotation of the Earth, and tries
| to cancel it out, just like it would cancel out your hands
| shaking. But while it's good to cancel out your hands shaking
| (because that's a motion that's independent of the subject of
| the photo), it's not good to cancel out the rotation of the
| Earth (because the subject of the photo is actually moving with
| you).
| thrdbndndn wrote:
| > 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.
| Filligree wrote:
| 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.
| Karellen wrote:
| The same axis of rotation? Pretty sure they're about
| 23deg off.
| Filligree wrote:
| Alright, close-ish to the same axis.
| SamBam wrote:
| It does. A perfect gyro will remain on a single axis
| relative to the rest of the universe while the Earth goes
| around the sun, and while the galaxies swirl around.
|
| I'll leave it to you to figure out how "perfect" it would
| need to be, and what the actual error that the stabilizer
| would need to account for if the gyroscope is accurate
| enough to detect the motion of the Earth around the sun,
| compared with the error created by the Earth's rotation.
| llm_trw wrote:
| The position of the gyro is attached to the earth surface but
| its orientation is not. See Foucault's Pendulum.
| exitb wrote:
| https://youtu.be/1zJ9FnQXmJI
| mikewarot wrote:
| We all want to keep missiles out of the hands of bad people.
|
| Parts to make _really good_ cameras could be taken out and used
| in missiles, to tell them where to go.
|
| So we now have laws to keep those really good parts out of
| cameras, for safety. Cameras still work fine, but you need a
| tripod to get good pictures when it's dark out.
| imglorp wrote:
| Is a plain phone gyroscope enough to detect Earth rotation? Is
| there an app for that?
| Delmololo wrote:
| You should be able to calculate it out by telling the user to
| press a button and after this, not rotating the camera away.
|
| Right?
|
| Might just not be practical at all.
|
| On the other hand, shouldn't the earth rotate fast enough to
| figure this out in a short timeframe while the photographer
| starts looking through the finder?
| mikhailfranco wrote:
| Yes, basically Method (2) with stable measurement window. Just
| put the camera down on a stable surface, click button. Let
| system wait some ms to allow click disturbance to pass, then
| integrate signal over some fixed time to establish the
| rotation, then pick up and continue...
| gwill wrote:
| i'm curious how the OM-1 MK2 gets around this to achieve 8.5
| stops.
|
| https://explore.omsystem.com/us/en/om-1-mark-ii
| eggy wrote:
| 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 also rotate and revolve in the same direction
| - Mercury, Earth, Mars, Jupiter, Saturn, and Neptune. A sidereal
| day is 23h 56m 4.091s for distant stars to return to the same
| spot in the sky.
|
| Damn, I knew that is why I botched my 6-stop exposure at my
| daughter's graduation! She can't blame me now! Thank you HN!
| trhway wrote:
| >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.
| eggy wrote:
| I shot competitively in JROTC and after, but never out to
| 1000 yards (914 m), only 500 yards. The Earth's rotation
| affects your trajectory significantly particularly if you are
| shooting longitudinally at a target at a higher or lower
| latitude. The Coriolis effect. I had more issues with varying
| winds or being consistent across shots.
| _ph_ wrote:
| 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.
| pixelpoet wrote:
| Yet another example of b0rked / unescaped TeX, specifically log
| vs \log in this case. Blows my mind that nobody sees it...
| cesaref wrote:
| This is analogous to astro-photography problems with keeping
| stars as points rather than as blurred lines in long exposures.
| If you think about it, if a long exposure at night has a static
| landscape but moving stars, the IBIS equivalent would have static
| stars and a moving landscape :)
| sib wrote:
| Nikon claims 8.0 stops of "VR image stabilization" for their Zf
| camera (released late in 2023).
|
| https://www.nikonusa.com/p/z-f/1761/overview
|
| ("Based on CIPA standards; when using the telephoto end of the
| NIKKOR Z 24-120mm f/4 S" - for clarity, that lens does _not_ have
| optical VR in the lens itself, so this is all based on in-body
| stabilization.)
| aidenn0 wrote:
| You should be able to exceed 6.3 stops if you are pointing
| north/south rather than east/west, right? Maybe they are just
| measuring it pointing north/south.
| chris_va wrote:
| 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).
| felixhandte wrote:
| That would only work in the case that the camera is fixed on a
| tripod and has a long period of stable / rigid pointing before
| the exposure during which to collect this data. This is
| sometimes the situation in which image stabilization is used.
| (But if you can be that stable for that long on a tripod, you
| may not actually need image stabilization.)
|
| By far the more common case for image stabilization is one in
| which the photographer is hand-holding the camera and may not
| frame the subject until the moment before the exposure begins.
| The camera movement will likely be _several_ orders of
| magnitude (~4 to 7) larger than the drift that you want to
| measure. A low pass filter will tell you nothing at all.
|
| At a certain point we can just start using guide stars [0].
|
| [0] https://en.wikipedia.org/wiki/Guide_star
| mrandish wrote:
| Perhaps in some camera firmware bug database there's a closed bug
| marked: "Won't fix. Tested working in orbit."
| mikewarot wrote:
| Bullshit. It's ITAR, they don't want parts floating around in the
| world that can make a dead nuts accurate INS - inertial
| navigation system, as this enables weapons we don't want in the
| wild.
|
| You can stabilize out everything and account for the rotation by
| simply watching the vector of gravity over time.
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