All is in the pictures.
View attachment 6704
@Leda Very clever! ??The mirror glass was cut from a simple and cheap pocket mirror. For cutting glass, I learned from tutorials in YouTube.
The copper wire is a part of an electric wire.
Both things were linked with some glue.
You can mount it on the Tello and dismount it very easily and without any tampering with the drone.
The result isn't a top quality optical device. But after cleaning the mirror and tuning the curves of the wire, I found it satisfactory.
Regards.