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by excuse-me
5126 days ago
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The proposed adaptive optics imager for ELT has a (1 sigma/1hour) limit in the visible of a 32mag object - with better than HST resolution. A 0mag star gives you about 1000photons/s/cm^2/Angstrom so the 40m telescope in visible light would capture about 2E13 photons/s for the brightest star in the sky. But 32mag is 2.51^32 = 6E12 times fainter so only a few 1000 photons in an hour long exposure. |
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