xkcd #3182: Telescope Types

Title text:

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.

Transcript:

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Source: https://xkcd.com/3182/

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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.
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[–] 1 point 9 months ago

Same, but I don't think I've seen 10 movies in that genre

All I can think are

  1. Comet in the Moominland (this was pretty scary one)
  2. The core
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