I was an owner of a Horseman SW612. You are not going to like the 45mm as the image circle barely covers the format at f/11, which is where mechanical vignetting ends. The 55mm is better, but needs to be stopped down to f/11 to eliminate mechanical vignetting and then a center filter is need to eliminate natural vignetting. Panoramic cameras sound really interesting for astrophotography on paper. The reality is very different. Wide open is not just a matter of vignetting, there are a lot of abberations at those apertures--not attractive with point sources. You will need a lot of testing to figure this out.
Originally Posted by kurt765
If you are looking for an all-sky camera, fisheye lenses work better.