Question: do binoculars work in a mirror?
Answer: Do binoculars work on a mirror? - Quora. Assuming it's a perfect mirror, then yes. But there is no such thing as a perfect mirror, so the quality of the image may get blurred and degrade. You might still be able to see an object 1 km away, but perhaps not an object 2 km away that you wouldn't otherwise be able to see.