system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do sniper rifle scopes work?

What are they made of? How can they magnify so far?
gpt
They contain little pieces of glass called lenses.  These lenses take the light that enters the front of the scope and stretch it out.  In the process of making the image bigger, the lenses flip the image upside down, so more lenses that flip the light right side up again are also inside the scope.  Either a piece of thin filament or a laser etching on one of the lenses creates an image of a cross hair that overlays the magnified image.  Some of the lenses are attached to swivels that you can adjust to make the crosshair match up with where the bullet will impact.  The more precisely  the lenses are manufactured (fewer surface errors, better concave and convex shaping) the more magnification will be possible without making the image fuzzy/dark.  That's why some scopes are so expensive, the higher quality materials and manufacturing produce a higher quality image.