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/


Had to sell my Meade LX200 12" to pay for medical bills a number of years ago. Made me very sad.
How to say you’re from the US without saying you’re from the US. Sorry, man.
Very much got USA’d in the middle of trying to grow a business. Ended up losing basically everything and starting over in life, out of everything though, that telescope was the only thing I really miss.