Terrific work. My first thought was an overlay or compositing the image on top, but seeing your comments below I realize it is not. There are few things more rewarding than successfully pulling off an in-camera trick nowadays. In this digital age, it's so easy to write something off as an "effect", it's so nice to see people using their tools in the original manner rather than relying on fixing it later on a phone or computer. Anyway, cheers my friend!