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mawyatt
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Post by mawyatt »

I remember reading discussions of this combined method stating that the method could not be made any better than it is now, because the rotation of the Earth is detected by the and fools the system into trying to compensate for it. This causes the system to take the wrong decision because the subject rotates together with the Earth and the camera, so no compensation is actually required. Canceling out the Earth rotation signal in the calculations is not a trivial problem, since it requires both the direction of shooting with respect to the Earth axis and the latitude to be known.
ES,

I'm not sure I would buy that discussion, could you provide the reference please?

I have some older experience in this area as about 35 years ago I helped develop the earliest ultra high performance fiber optic gryo concepts based upon the Sagnac effect and patented an electro-optical Serrodyne modulator utllized to linearize the Sagnac effect (Sinusoidal ambiguous & non-linear), and an ultra low noice transimpedance amplifier used to detect the fiber rotating photons. These systems could certainly measure well below earth rate and are used in aircraft, satellite, space probes, missile and precision terrestrial navigation systems. However I don't think these fiber optics based systems have been refined enough to be in our cameras, and suspect the movement sensors in our cameras are simple capacitive MEMs types similar but much more sensitive than the automotive airbag sensors but not able to discern the earths rotational velocity and certainly not relativistic effects.

We must remember than accelerometers measure the time rate of change of velocity, and velocity is the time rate of change of distance which requires a reference position. Since the camera at rest and earth's surface are moving in unison as a reference the time rate of change in relative velocity of the camera is zero unless the camera is moved. Also if the camera is moved at constant velocity the result is also zero.

I don't see how the sensors in our cameras can measure or even respond to the earth's rotation (which is quite constant) since they are simple accelerometers. I admit I haven't delved into this particular gryo/accelerometer subject in a long time, so maybe some progress I'm not aware of has been achieved. If so, please enlighten me.

Best
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike

ray_parkhurst
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Post by ray_parkhurst »

Macro_Cosmos wrote:
ray_parkhurst wrote: Pixel shift would not be very useful at high mags. Getting higher resolution by pixel shifting requires the information presented to the sensor to contain information worth shifting for. A 10x 0.28 Mitty is at f18, so you're not going to be extracting much sub-pixel information from it.
Yeah, that's one point.
Another point would be the precision of pixel shift. Pixel shift as it currently is just cannot handle the precision required for high-mag. work. A friend tried this on his H6D-400C, the results were just abysmal. He didn't even use objectives. The lens was a Hassy 120mm Macro, and that alone presented so many complications leading to a tosser. Basically a nearby construction site also contributed to the blurry exposure... and we're talking about 1:1. 5:1? Yeah... So pixel shift doens't interest me at all. It's a good qwerk, there's however lots of improvements required.
I guess you're just referring to vibration effects making it impractical to achieve accurate sub-pixel registration, but of course the lack of information in the image would keep you from even trying.

Steve S
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Post by Steve S »

Regarding stabilization systems and the rotation of the earth, it does initially sound like rubbish, but a couple of DPReview threads from 2016 have a few thoughtful posts that may persuade you otherwise:

https://www.dpreview.com/forums/thread/4059288

https://www.dpreview.com/forums/thread/4062280

The basic idea is that the gyros locate the camera with respect to an inertial frame of reference, while the world spins on, rotating the subject with it. Think of the Coriolis "force" -- not a force, really, but a kinematic effect. Takes me back to Ph106 at Caltech in the '50's.

Back-of-the-envelope calculations in the threads above have the effect something like an order of magnitude below the ~3 stops I see in practice with Sony and Nikon, so maybe not to worry.

mawyatt
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Post by mawyatt »

Steve S wrote:Regarding stabilization systems and the rotation of the earth, it does initially sound like rubbish, but a couple of DPReview threads from 2016 have a few thoughtful posts that may persuade you otherwise:

https://www.dpreview.com/forums/thread/4059288

https://www.dpreview.com/forums/thread/4062280

The basic idea is that the gyros locate the camera with respect to an inertial frame of reference, while the world spins on, rotating the subject with it. Think of the Coriolis "force" -- not a force, really, but a kinematic effect. Takes me back to Ph106 at Caltech in the '50's.

Back-of-the-envelope calculations in the threads above have the effect something like an order of magnitude below the ~3 stops I see in practice with Sony and Nikon, so maybe not to worry.
Steve,

Thanks for the DP sites and enlightening me. :D

I had no idea that MEMs based sensors had evolved to be anywhere close to where the earth's rotation would have an affect. 6.5 stops is still aways below the present stabilization, but not as far away as I had thought. :shock:

I know Honeywell and DARPA have been working with trying to integrate fiber optic gyros (FOGS) to achieve much higher sensitivity than MEMs based gyros, and have progressed a lot since my days in 1984~87 with some of the 1st FOGS where we were getting short term Ring Laser Gyro (RLG) performance from our FOGs, but must admit the MEMs are much better now also!!

Just noted you are in Arizona, I worked with the Sperry/Honeywell group on the FOG in Phoenix during the mid 80s.

Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike

Beatsy
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Post by Beatsy »

Tonight, I got a first hand report from (and a lengthy, interesting conversation with) an R&D guy who works at a company that shall remain nameless. They've been evaluating MEMS based gravity sensors that can detect a person walking around them - from the gravitational effect alone :shock:

Technology is grand!

Lou Jost
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Post by Lou Jost »

Wow Steve, that's scary!!!

Lou Jost
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Post by Lou Jost »

Returning to the point about pixel shifts, as long as the EA is below about 8 (on an MFT sensor), pixel shifting does add real resolution, regardless of magnification. Of course you have to control vibrations, but that's not the fault of pixel shifting algorithms, you have to do that anyway if you are trying for high resolution.

ray_parkhurst
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Post by ray_parkhurst »

Lou Jost wrote:Returning to the point about pixel shifts, as long as the EA is below about 8 (on an MFT sensor), pixel shifting does add real resolution, regardless of magnification. Of course you have to control vibrations, but that's not the fault of pixel shifting algorithms, you have to do that anyway if you are trying for high resolution.
I do understand MacroCosmos' point about vibration. I have struggled with my setup to get vibration at ~1:1 below 1 pixel after settling, but indeed at higher mags it's really near impossible. My setup is about as rigid and coupled as it can be, yet at 10x I can still see "random noise" movements in the Live View output, and at 20x they are very visible, even though the resolution is >>1 pixel. The classic way to eliminate this is with flash, and indeed this can work for standard stacking, but it will capture the image at a random viewpoint. That random viewpoint would be anathema to the pixel-shift algo, since it could never count on the viewpoint being the correct sub-pixel one needed for compositing.

Lou Jost
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Post by Lou Jost »

Yes, you are right, I had forgotten that. Pixel-shifting photos cannot be "saved" from vibrations by flash, as single images can be saved by it.

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