In article , Ken Hart
wrote:

But the biggest lens I've seen in real life was a nikon 6mm fisheye in the
mid 70s.

I've never seen that lens in real life, but I remember the "excitement"
when it was introduced. I googled it, and found

https://www.mir.com.my/rb/photograph...rces/fisheyes/
6mmf28.htm
has a pretty nice writeup about it.
For those who just want the highlights: a 220 degree angle of view,
236mm (9.29") diameter, 171mm (6.73") long, weight 5.2Kg (11.46 pounds).
The website doesn't give a price, but mentions that it was special order.

$6k in 1970s dollars.

$161k today, due to its rarity, at least this one:
https://www.theverge.com/2012/4/24/2...on-6mm-f2-8-le
ns-for-sale-london