This lens is the best entry point fisheye on the market. Price is typically around $300-$400 USD and it is sold under many names.
Including:
Samyang, Falcon, Polar, Opteka, Rokinon, Vivitar, Bower, Walimex Pro among others.
In some cases it is marked as a 6.5mm or 7.0mm but all are the same Samyang 8mm Fisheye lens with the Vivitar the only to have a updated "sexier" design and look.

It is a fully manual lens, meaning it has no electrical contact to the camera body. So focus and aperture settings are all done manually, which is no biggy as you will most likely settle on an aperture and hyperfocal distance and never change them.
Though the manufacturer claims it to be a 8mm lens, PTGui results show it is more like a 9mm lens and this comes down to its unusual stereographic projection.
Shooting configuration on a APS-C sensor camera is as little as 4 rotational shots + zenith shot (4+1z).

This example shows 4 shots at -15 degrees and 1 zenith shot at +60 degrees.
It is advisable to shoot 5 or 6 -15 degrees rotational shots with double zenith shots +60 180 degrees opposed (5+2z) or (6+2z).
This gives you greater overlap and generally much better places for control points.
You can read more on this in my original thread on another forum.
Regards, Smooth
