From what I've been reading, a more expensive fish-eye lens will give
you auto-focus capability, which is a waste of money given that these
will only really work properly at infinity. Anyhow, this lens seems to
be a reasonable price, given that a fish-eye is not an everyday lens.
As for the Peleng, i can't compare it to any other fisheye, but if i compare larger prints (DinA 2) i need to admit, that the Peleng-pictures look a bit dull. Still, the pictures look good, but not as brilliant as pictures taken with the zuiko 9-18 for example (less detail as well). Also it might be because of some chromatic aberration, i didn't take care of it and all the olympus lenses should produce less....i'm curious how the pictures will look with corrected CA.
Also it looks like flare is an issue...
Autofocus is definitively not necessary with a fisheye, also it could come in handy with some close ups....
Well anyways, it is a really good lens if you want to find out if you like fisheye photography (like me), but i halfway regret not to spend three times as much on a descent fisheye...
...maybe i am a bit hard on the peleng, did i mention that i really do like it a lot?
The rainbow haloes at the fringes will be your best guide.
If you use GIMP, do a search for 'Fix-Ca' and you will find out why
I associate sea-turtles with Chromatic Aberrations.
The better lens coatings probably help a little but flare is a real problem. Lots of CA at the edges.