Never mind. I now understand the whole business about many NPPs with fisheye lenses from the site Hugh mentioned. Thank you.
Now I am down to 2 choices: the Sigma 10-20mm or the Samyang 8mm. I like them both equally because they are both inexpensive and will help reduce the number of images I need to take. For me, the big thing going for the Samyang is the price. On the other hand I find the multiple NPPs confusing and I am a little scared I may never figure out how to work with it. The big thing going for the Sigma is that It can also be used for 'general photography' and I can buy it locally, here in Ottawa. I don't like shopping online (buying my Nodal Ninja MK3 from the estore was a big deal for me).