When I was getting started in photography seriously, let’s call it the 1970s, I don’t think any lens wider than 21mm was at all commonly available for 35mm photographers. Oh, there were a couple of fisheyes, including Nikon’s monumental 6mm f/2.8; and their 15mm rectilinear came out in 1973, but I never heard of it then.
A few years have passed since then, and today UPS delivered to me a 12mm rectilinear wideangle. In fact, a 12-24mm zoom. For full-frame 35mm (film or digital).
12mm. I’m still appalled.
Here’s a fairly ordinary view of my room (which will be a bit surprising to people familiar with it).
And here’s a rather more interesting view from close to the same location.
I am a happy camper.
(Sigma 12-24mm f/4.5-5.6. Slow, bulgy, fragile, large. And remarkably cheap with a little shopping (I beat the B&H price on the day I ordered it by $200, which is unusual from any vaguely reputable dealer).)