Hi
thought you may find these interesting, enjoy, Ian

Snell’s Window

https://www.divephotoguide.com/underwater-photography-techniques/article/underwater-photographer-s-guide-snell-s-window-martin-edge/

An In-Depth Guide to Shooting Snell’s Window 

https://www.divephotoguide.com/underwater-photography-techniques/article/underwater-photographer-s-guide-snell-s-window/