4 ms·

I'd imagine the math to be off-the-charts complicated, but I'm interested in the signal processing software people have created for correcting optical aberratio

I'd imagine the math to be off-the-charts complicated, but I'm interested in the signal processing software people have created for correcting optical aberration (and how effective it is). I believe they pioneered this technology for the hubble's mirror defect. If it's effective, then manufacturers could reduce costs by not even needing to try for perfection, just staying within the limits of what software can fix.

dandelany 10y ago
Yeah this is an interesting area of research - I think the term you're looking for is deconvolution. Here's a document about some of the work done for Hubble in this regard (large PDF): http://www.stsci.edu/hst/HST_overview/documents/RestorationofHSTImagesandSpectra.pdf http://www.stsci.edu/hst/HST_overview/documents/Restorationo... However, my understanding is that you can improve things but you can't "truly" correct it, generally speaking, because the optical aberration causes information to be lost. eg. if point A on your mirror focuses to point A' on the resulting image, and point B on your mirror, due to an aberration, also focuses to A', there's no way to determine from the image which point on the mirror a photon came from. This is why Hubble eventually needed a hardware fix... from the linked paper: "it is clear that many image restoration methods are highly successful at deriving images that 'look good' from HST data. These restored images may be qualitatively faithful to the true (unknown) image. However, for most astronomical purposes qualitative agreement with reality is not sufficient; we want quantitative agreement as well."
dekhn 10y ago
The approach most advanced people use now is deformable mirrors. They work in concert with a laser that emits from the detector, bounces off the atmosphere, and produces a real time map for the deformation (you have to solve an inverse problem here IIRC). You can also use a wavefront sensor. For small problems, you can just buy these things off the shelf: https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3258 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=32... "only" $17.5K
- nomel 10y ago
  The history behind wavefront sensors is pretty fascinating. It was developed in the 60's by Hartmann, in order to better image satellites from earth, and then largely ignored by the astronomy community, even though he presented it to them, until the 80's. I can't find the original paper that I read, but here's a bit of history [1]. [1] https://pdfs.semanticscholar.org/d1ed/a97dd2cf70f54f24b85abc320915cab1be4a.pdf https://pdfs.semanticscholar.org/d1ed/a97dd2cf70f54f24b85abc...
  - dekhn 10y ago
    WHen I started grad school in Biophysics (1995), a microscope professor mentioned adaptive optics and asked the incoming students if they thought similar processes could be done in microscopy. If you said yes, he let you join his lab (they were already working on this).
    - digler999 10y ago
      I wonder if it would be possible to make a deformable mirror using a combination of liquid mercury chemically bonded with a ferromagnetic metal (if mercury isn't already magnetic). Then theoretically, you could use an electric current in a coil to shape the liquid into a precise shape.
      - dekhn 10y ago
        Maybe? I wouldn't touch mercury for any reason, though.
    - nomel 10y ago
      Oh interesting! Were they working with some sort of fluid interface? Maybe layered liquids, or fluids that you don't want to dip an objective lens into? Or maybe temperature gradients?

dandelany 10y ago

Yeah this is an interesting area of research - I think the term you're looking for is deconvolution. Here's a document about some of the work done for Hubble in this regard (large PDF): http://www.stsci.edu/hst/HST_overview/documents/RestorationofHSTImagesandSpectra.pdf http://www.stsci.edu/hst/HST_overview/documents/Restorationo... However, my understanding is that you can improve things but you can't "truly" correct it, generally speaking, because the optical aberration causes information to be lost. eg. if point A on your mirror focuses to point A' on the resulting image, and point B on your mirror, due to an aberration, also focuses to A', there's no way to determine from the image which point on the mirror a photon came from. This is why Hubble eventually needed a hardware fix... from the linked paper: "it is clear that many image restoration methods are highly successful at deriving images that 'look good' from HST data. These restored images may be qualitatively faithful to the true (unknown) image. However, for most astronomical purposes qualitative agreement with reality is not sufficient; we want quantitative agreement as well."

dekhn 10y ago

The approach most advanced people use now is deformable mirrors. They work in concert with a laser that emits from the detector, bounces off the atmosphere, and produces a real time map for the deformation (you have to solve an inverse problem here IIRC). You can also use a wavefront sensor. For small problems, you can just buy these things off the shelf: https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3258 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=32... "only" $17.5K

nomel 10y ago
The history behind wavefront sensors is pretty fascinating. It was developed in the 60's by Hartmann, in order to better image satellites from earth, and then largely ignored by the astronomy community, even though he presented it to them, until the 80's. I can't find the original paper that I read, but here's a bit of history [1]. [1] https://pdfs.semanticscholar.org/d1ed/a97dd2cf70f54f24b85abc320915cab1be4a.pdf https://pdfs.semanticscholar.org/d1ed/a97dd2cf70f54f24b85abc...
- dekhn 10y ago
  WHen I started grad school in Biophysics (1995), a microscope professor mentioned adaptive optics and asked the incoming students if they thought similar processes could be done in microscopy. If you said yes, he let you join his lab (they were already working on this).
  - digler999 10y ago
    I wonder if it would be possible to make a deformable mirror using a combination of liquid mercury chemically bonded with a ferromagnetic metal (if mercury isn't already magnetic). Then theoretically, you could use an electric current in a coil to shape the liquid into a precise shape.
    - dekhn 10y ago
      Maybe? I wouldn't touch mercury for any reason, though.
  - nomel 10y ago
    Oh interesting! Were they working with some sort of fluid interface? Maybe layered liquids, or fluids that you don't want to dip an objective lens into? Or maybe temperature gradients?