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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)

#41

Post by poulpy123 »

noselasd wrote: post #40
kqr wrote: post #2

6.3 stops is a lot, though. That's basically the fully usable aperture range of a kit zoom lens.

What are these "stops" in this context, for the non-photo nerds ?

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

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

#42

Post by vouaobrasil »

kqr wrote: post #2

6.3 stops is a lot, though. That's basically the fully usable aperture range of a kit zoom lens.

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.

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

#43

Post by moi2388 »

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?

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

#44

Post by formerly_proven »

noselasd wrote: post #40
kqr wrote: post #2

6.3 stops is a lot, though. That's basically the fully usable aperture range of a kit zoom lens.

What are these "stops" in this context, for the non-photo nerds ?

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.

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

#45

Post by SamBam »

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…

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).

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

#46

Post by SamBam »

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 already does this.

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

#48

Post by llm_trw »

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…

The position of the gyro is attached to the earth surface but its orientation is not. See Foucault's Pendulum.

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

#49

Post by nick7376182 »

isoprophlex wrote: post #13

> 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…

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.

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

#50

Post by matthew-wegner »

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…

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...

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