Thank you Interceptor,
We build the WACP-1 and WACP-2 for underwater photographers who demand superior image quality at larger apertures, such as f/5.6 or even f/4. While the WACP-2 in combination with the Nikon 14-30mm results with 140° AOF images with quite low distortion, and very good image quality across the frame, our main objective is not aiming for zero distortion.
First of all, zero distortion doesn't exist at all for any lens in the wide angle range of 130° to 140°. For example, the Canon 11-24mm (max AOV 126°), the Nikon 12-24mm (max AOV 122°) and the Nikon 14-30mm (max AOV 114°) all have certain amount of barrel distortion at the wide end. Naturally, the WACP-2 as an afocal add-on lens mounted in front of a lens having barrel distortion, it will be not able to eliminate the inherent barrel distortion.
Using any of these wide angle zoom lenses behind a dome port also doesn't help with barrel distortion. Until now we haven't seen anyone to be able to produce perfect zero distortion images using one of these wide angle lenses behind a dome port. Of course, the normal dome port theory applies here! People can't achieve relatively good sharp corners until closing down the apertures to around f/14, and a dome port could actually induce more barrel distortion to the system. Adding a corrective lens in front of the camera lens may further complicate the issue because it introduces another type of distortion to the system.
There is now a 12mm (AOV 122°) lens in the market that claims to have zero distortion, at the price of heavily and unnaturally stretching the images at the corners. It is fine for shooting buildings, but any subject, in particular people, will look extremely unpleasant if placed near the corners. The result of using this lens behind a dome port is yet to be found out.