Looking to Purchase a third lens or accessories - ideas?

[matphotographs]

Hi! I am new to the community, but I am looking for advice!

I currently own a 6D Mark II with a 24-70mm f4 and a 70-200mm f4, and I am looking to purchase another lens.  I mostly do landscape, headshots, and astrophotography.  From a lens standpoint, my current lenses satisfy landscape and headshot needs for the most part, but I was hoping to get recommendations for astrophotography lenses that could also compliment landscape and headshot work!

I'd love any feedback/recommendations!

Thanks!

[ChrisPBacon]

I have been using an EF 15mm f/2.8 and EF 24mm f/1.4L II USM for adtrophotography, and am considering  purchasing an 

EF 14mm f/2.8L II USM if I decide against buying a Zeiss Milvus 15mm f/2.8 ZE lens,].