Originally posted by UserAccessDenied I've been looking at the SamBoRoki's 14/2.8; 10/2.8; 8FE/3.5
I think these and the Samyang 24mm f1.4 are generally accepted to be some of the best lenses for astrophoto, and not just because of their wide angle, fast aperture, and good price (though, all of that helps!). Its mostly about high resolution and lack of coma. You don't want to spend big money to get a lens that is UWA, but has some optical features that make it less than ideal for astrophotos.
But if you already had 16mm and don't miss it desperately, maybe it doesn't make sense to buy another copy of the same lens. The 14mm is a little wider and FF compatible. The 10mm is wider, still! Super, dramatically wide. Fisheye is interesting, but very different lens. So maybe try one of the other UWA Samyang lenses that fit the Field of View that you want to capture.
Pentax makes some nice WA lenses (21mm, 15mm) which probably render contrasts similarly to the DA 35mm ltd. But those lenses have much slower aperture and higher price point than the Samyang. Lots of people love the 15mm ltd and 21mm ltd for night photos.
Since you have the astrotracer, you might want to just try the 35mm ltd first. If you have a basic zoom lens like 18-55mm, you can do a test with that to see which focal lengths you want next.
I quite enjoy my Pentax M 28mm, I like its FoV. But it is not exactly very wide angle on APSC cameras. For astrophotos I think you want wider than 26mm, especially on APSC