Originally posted by UncleVanya The claim is that the info isn’t lost until about f11 and that with a clean low iso signal well understood predictions can restore some of the information. I’m continuing to look into it.
Well, you can sorta cheat.
Radio astronomers have been using the CLEAN technique (
https://en.wikipedia.org/wiki/CLEAN_(algorithm)) for quite some time. The gist is to find the peak in an image, and subtract some fraction of what you know the imaging device point source response shape looks like (the diffraction spot, aka Airy Disk, for an optical camera) from the image, centered on that peak position. The typical radio astronomy interferometer beam map is quite messy, in terms of sidelobes, and this technique works AMAZINGLY well. It was an integral part in making that "first map of a black hole" for the galaxy M87 a while ago. (As an aside, I was the first person in the world to actually KNOW that M87 had a compact radio source in it, back around 1970 or 1971 when I was a graduate student manning the night shift at the computer center where we were processing our VLBI (
Very-long-baseline interferometry - Wikipedia) data tapes.)
A similar scheme was used to improve the early images from Hubble Space Telescope, back when it first went into operation with its mis-figured mirror and produced some rather ugly images.
How well this all works depends on the signal-to-noise ratio, and how well you
really know the point-spread function (PSF).
i.e. for our cameras, the apertures are not round (which is what an Airy disk is calculated for), so a more complicated PSF is needed to dig very deep. And, it probably varies across the image, as a function of look angle back out through the iris and lens.