Just saw this: https://www.sonyalpharumors.com/crazy-sigma-will-announce-a-new-15mm-f-1-4-diagonal-fisheye-lens

 

Finally a native E-mount autofocusing fisheye? Not sure the f/1.4 aperture is of any use underwater though.

I hope the f/1.4 is a "silent post" error and in fact it is a 15-35mm zoom fisheye of the "art" optical grade...

 

Really interesting, but it is unlikely it will replace my Canon 8-15mm fisheye in case it is just a prime lens...

 

 

Wolfgang

One thing to watch on very fast lenses - is that they can't be stopped down as much. A fisheye that was limited to f/16, for example, would be compromised for split level shooting. 

The other thing to watch is the physical length of the lens. Too short and it might not stick out far enough on some housings to work with a port.

 

But pass these two tests and it will be definitely preferable to a fisheye on adapter.

F/16 smaller aperture is possible