@loganlamar, if you are to be using it for astrophotography, I think the expanding focal length and the large aperture would be a great asset. Also, the 2mm difference between the 18-200 and the Rokinon is so tiny that probably the only reason from my point of view to get the Rokinon would be for the sharpness throughout the lens. From my point of view, you don’t need autofocus if you’re doing astrophotography, because you can’t see anything to focus on.
