system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't I use a telescope to look at really small things? Why can't I use a microscope to look at things that are far away?
gpt
Focal length.

Microscopes use shorter focal length to view small objects, while telescopes use longer focal length to view far-away objects. 

Focal length is basically where the image is located relative to the lens. A shorter focal length means that you can resolve images that are very close to the lens, while a longer focal length means that you can resolve images that are very far from the lens. 

It's sort of like trying to design a laser vs a flashlight. Lasers must be very focused to be useful for the tasks they're designed for, but flashlights should be dispersed to illuminate more area and not blind people. A laser makes a bad flashlight, and a flashlight makes a bad laser.