Comment on xkcd #3182: Telescope Types

abigscaryhobo@lemmy.world ⁨1⁩ ⁨day⁩ ago

• bort@sopuli.xyz ⁨1⁩ ⁨day⁩ ago

  The wire will cause the entire image to become a little bit darker.

  in a telescope light travels in many paths from start to finish. so a single wire will have a very soft shadow, which stretches over the entire image. This works because the wire is well within the focal length. If the wire was exactly at the focal length, it’s shadow would be sharp, but the farther away it is from the focal length, the softer the shadow will become

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  • Successful_Try543@feddit.org ⁨1⁩ ⁨day⁩ ago

    The wires also bend the light which makes the stars not look like points but gives them prongs.

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  • RaccoonBall@lemmy.ca ⁨20⁩ ⁨hours⁩ ago

    for similar reasons cracked camera lenses take perfectly normal pictures

    definitely a bit counter intuitive at first

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• KingRandomGuy@lemmy.world ⁨17⁩ ⁨hours⁩ ago

  Like others have mentioned, the spider (the wires) and the secondary do shadow some light that would otherwise reach the primary. It also results in some artifacts due to diffraction; the view ends up convolved with the Fourier transform of the aperture. This is why on Hubble images, you see cross shaped stars, as that’s the shape of the Fourier transform of its 4-strut spider.

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• Munkisquisher@lemmy.nz ⁨1⁩ ⁨day⁩ ago

  It will only affect it materially if they cross where the light is converged / infocus. So if you put a big piece of paper where the wires are, the image will be blurred. So if you look at the wires from the focal point, they are also blurred enough to be able to see what’s behind them

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• Wrufieotnak@feddit.org ⁨1⁩ ⁨day⁩ ago

  Not an expert, but as far as I know, you nearly never see a true single picture, but always a combined one. So they take multiple slightly overlapping pictures who are seeing the hidden middle spot of other pictures.

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