I think if using a spinning disc with cutouts for the variable
coded aperture, to have an optimal placement of cutouts, I think
2D golomb rulers, or Costas array's would work:
On 2019-01-11 5:41 a.m., Jamie M wrote:
On 1/11/2019 1:52 AM, Martin Brown wrote:
On 10/01/2019 12:51, Jamie M wrote:
On 1/10/2019 2:03 AM, Martin Brown wrote:
The aperture would have to introduce a uniform phase delay if it
was to work at all. Mainly coded apertures allow you to alter the
depth of field after taking the image data but when everything you
are looking at is effectively at infinity this is not an advantage
in astronomy and merely degrades signal to noise with no benefits
Imagine a simple case of a single pixel detector, and an LCD coded
aperature with 4 pixels (square 4 quadrant detector)
pixel detector----(1000km)----(4 pixel LCD)---(10light years)----(star)
If the star when viewed with the hubble telescope, has a huge sunspot
on the upper left of it's visible hemisphere, then the single pixel
detector in conjunction with a 4 pixel LCD that has 3 pixels active
time alternating the dark pixel, will produce a brightness signal
at 1/4 the frequency of the pixel step frequency, as every 4th change
in the LCD pixel configuration would darken the upper left pixel, which
would mean the rest of the star is not darkened by the LCD and thus
brighter when viewed by the single pixel detector.
Congratulations. You have reinvented the pinhole camera.
A pinhole lens camera has a single small aperture and projects the image
onto a CCD, not sure how you confuse that with the 4 pixel coded
aperture I described.
It would be a lot more efficient to use an actual telescope and a
pixel LCD but the concept is the same, except for the specific pattern
of active/blanked pixels would depend on what part of the image is
desired to be resolved more etc.
There is no phase delay issues it is just simple light masking, and
would increase angular resolution of a telescope.
You really are utterly clueless. The incident wavefronts must remain
coherent through the optical chain to make a diffraction limited image.
Assuming the waveform isn't coherent is just ignoring the main idea of
using a variable coded aperture to effectively increase angular
resolution of a telescope, in favour of irrelevent details. Here is a
simple fix if you are too lazy to imagine a sufficiently flat LCD
masking screen to keep phase error low enough:
Replace the transparent LCD with a laser cut stainless steel sheet, with
concentric cutouts in the same idea as a DVD optical disc. The cutouts
will pass the light from the star with no impact on the light as
it is travelling through free space. Rotate the stainless steel sheet
on its axis, axially between the telescope and the object(s) being
imaged to have the effect of creating a repeatable variable coded
The moon dark side occulting stars and radio sources has in the past
been used as a means to determine their position. Back in the days
when radio telescopes all had very poor resolution. These days star
positions are known so well it is used by amateurs to determine the
heights of mountains at the lunar limb in grazing occultations.
A very lucky occultation of a fairly bright star by Titan gave the
first hints that it had an atmosphere in 1989. There is a video of it
(link seems to have vanished). A diffraction peak at mid eclipse was
predicted but it was way brighter than expectations from a pure
geometrical disk. The atmosphere boosted the signal.
Looking for microlensing by compact objects passing in front of
distant stars is an active area of research.