I'm thinking of adding a super-wide zoom to my Nikon F-mount system (Nikon F & Nikomat FTn). This idea didn't occured to me until I realized there were some third party manual focus super-wide zooms like Sigma 21-35mm F3.5-4.0 (or F3.5-4.2). I had long thought I had to select from AF zooms if I want a super-wide zoom for my MF Nikon bodies. Now I'm wondering if there's any other manual focus super-wide zoom other than the Sigams. Is there any other decent manual focus super-wide zoom? Are they worth looking for, or should I just stick to using primes for my old Nikons? I know AF zooms can be used with MF Nikons as long as they have aperture rings, but I'm looking for a manual focus zoom this time, and I'm looking for those which goes wider than 21mm.

Thanks in advance!