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Thread: Telescopes with non-circular pupils

  1. #1
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    Lightbulb Telescopes with non-circular pupils

    I do not know if this design applies to backyard observing, but it might to high-grade personal telescopes. Good for photography? Hope it helps.


    https://arxiv.org/abs/1809.09933

    A possible advantage of telescopes with a non-circular pupil

    Guy Nir, Barak Zackay, Eran O. Ofek (Submitted on 26 Sep 2018)

    Most telescope designs have a circular-shape aperture. We demonstrate that telescopes with an elongated pupil have better contrast, at lower separations, between a bright central star and a faint companion. We simulate images for an elongated-pupil telescope and for a circular-pupil telescope of equal aperture area and integration time, investigating specifically what is the maximal contrast for finding faint companions around bright stars as a function of angular separation. We show that this design gives better contrast at lower separation from a bright star. This is shown for diffraction-limited (for perfect and imperfect optics) and seeing-limited speckle images, assuming equal aperture area and observing time. We also show the results are robust to errors in measurement of the point spread function. To compensate for the wider point spread function of the short axis, images should be taken at different rotation angles, either by rotating the telescope around the optical axis or by allowing a stationary mirror array to scan different parallactic angles with time. Images taken at different rotation angles are added using the proper image coaddition algorithms developed by Zackay & Ofek. The final image has the same contrast in all angles, rather than in specific areas of diffraction nulls. We obtained speckle observations with a small, ground based elongated-aperture telescope and show the results are consistent with simulations.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    Mark Twain, Life on the Mississippi (1883)

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    Cats' eyes!
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  3. #3
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    Quote Originally Posted by Trebuchet View Post
    Cats' eyes!
    I was thinking alligator or snake, but alas for me with seven cats, yes, cats too.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    Mark Twain, Life on the Mississippi (1883)

  4. #4
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    Everything old is new again! Vintage 1964, the Jodrell Bank Mk II radio telescope with 25x38-meter aperture (although built that way only incidentally for resolution reasons, mostly prototyping approaches for larger dishes where that would have been desirable to reduce the overall weight).Used on the ground with altazimuth mount, such a telescope automatically provides the kind of field rotation this paper describes between observations, so their combination give the PSF advantage all the way around instead of only along the long axis of the primary.
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