Hi Jean Yves,
In my book, "Math and the Mona Lisa," this staircase had appears in the color (signature) section, shot in the early 1990s with a 16 mm near-fisheye lens using a 35-mm Nikon N90 camera. That lens had a 140° angle of view from side to side. A true fisheye lens on the analogue camera that can shoot 180° from side-to-side has to have a focal length of 12-13 mm.
The Nikon D-70 I used for the present photograph was at the 18 mm wide angle limit. That compares with a 24 mm focal length on an analogue camera. The true fisheye lens for the digital camera for digital Nikon has a focal length of 10.5 mm, and costs $800. If I used it more, I could justify buying it.
Thank you for the kind remarks.