Fish eye Lens

[Danosborne6661]

I have a pretty basic camera for my needs. Just a Fuji s5500 but its a great
camera with alot of SLR features which is just what i wanted Anyways i
was just looking to get a Fish eye lens for it, ive been looking at a
few and noticed they are named like the following

-.22 Fish eye lens
-.42 Fish eye lens

You get some lens looking at samples that dont give off much of a round effect. I want one thats really sort of rounded. What shall i go for and what do the 2 samples above mean?