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:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3182/
Do not drink the liquid mirror!
I repeat. Do. Not. Drink. The liquid mirror!
But its shiny, and smells interesting.
But I’m so thirsty meow.
But bathing in the telescope is still fine, right?
You can only do it once
Instructions unclear, drinking straw stuck in telescope.
Forbidden juice…