Wider lens

[Evertking]

I am looking for a wider lens for landscapes and Astro stuff and on a budget. The first lens that caught my eye was the rokinon 14mm f2.8 but was reading that it can be difficult getting ND filters for that one. Then I am left with canons 24,28 and 35 non L lens. I was thinking that maybe someone owns these or has used some of these could help out. I will just use it for landscapes, night Photography and would love to get NDs for Long exposure day shots.
I currently have a Canon 6D
A 50mm, 85mm and a 135mm.

 

[480sparky41 40]

Look into ultra-wide lenses that have rear gelatin filter holders.