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/
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.