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Ask Ethan: Why don’t we build a telescope without mirrors or lenses? (Synopsis)

30 Sep 2017, 14:06 UTC
Ask Ethan: Why don’t we build a telescope without mirrors or lenses? (Synopsis)
(200 words excerpt, click title or image to see full post)

“Look and think before opening the shutter. The heart and mind are the true lens of the camera.” -Yousuf Karsh
Every time you shine light through a lens or reflect it off of a mirror, no matter how good it is, a portion of your light gets lost. Today’s largest, most powerful telescopes don’t even simply have a primary mirror, but secondary, tertiary, even quaternary or higher mirrors, and each of those reflections means less light to derive your data from. As CCDs and other digital devices are far more efficient than anything else, why couldn’t we simply replace the primary mirror with a CCD array to collect and measure the light?
This diagram shows the novel 5-mirror optical system of ESO’s Extremely Large Telescope (ELT). Before reaching the science instruments the light is first reflected from the telescope’s giant concave 39-metre segmented primary mirror (M1), it then bounces off two further 4-metre-class mirrors, one convex (M2) and one concave (M3). The final two mirrors (M4 and M5) form a built-in adaptive optics system to allow extremely sharp images to be formed at the final focal plane. Image credit: ESO.
It seems like a brilliant idea on the surface, and ...

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