yarn xkcd-com@feeds.twtxt.net "Telescope Types I'm trying to buy a gravitational lens for my camera, but I can't tell if the manufacturers are listing comoving focal length or ..."

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Tue, Dec 16 7:00PM (44w ago)

Telescope Types
I'm trying to buy a gravitational lens for my camera, but I can't tell if the manufacturers are listing comoving focal length or proper focal length. ⌘ Read more

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