Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

thecentercolumn.com

Post reply on HN
Print view View original

51–60 of 112 posts

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

#51

Post by Espressosaurus »

SamBam wrote: post #46
GuB-42 wrote: 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…

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!

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

#52

Post by Delmololo »

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?

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

#53

Post by Espressosaurus »

matthew-wegner wrote: post #50
SamBam wrote: 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…

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.

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

#54

Post by mikhailfranco »

Delmololo wrote: post #52

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?

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...

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

#55

Post by labcomputer »

crubier wrote: post #27
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…

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

> 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.

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

#57

Post by labcomputer »

Rinzler89 wrote: post #35
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…

> 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 MEMS gyro, but you're really at the limit.

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

#58

Post by [deleted] »

DoctorOetker wrote: post #15

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.

[deleted]

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

#59

Post by eggy »

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!

Post reply on HN