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AstroFocusInfo |
What should a star look like when perfectly in focus? Because light is a wave, when light from a star passes through a circular aperture (like a telescope lens) it diffracts -- light waves scraping the sides of the aperture spread out and interfere with each other. Rather than the telescope lens focusing the star to a perfect pinpoint, the best the lens can do is focus the light into a small disk ( called an airy disk) surrounded by faint diffraction rings like the image to the right. The airy disk can be made smaller (more pin-point-like) by using a telescope with a larger diameter objective lens or mirror but... |
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What does a star actually look like? But in the real world there are effects that preclude seeing a perfect diffraction-limited airy disk. Some you can't control, some you can.
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