Askar fma 180 or 135mm f2? (or something else)

[JJenks]

So I have about $400 to spend and I was thinking I would get a new lens for my Nikon D600. I currently have a 28-300mm f3.5-5.6 lens and a star adventurer pro 2i. The only lenses/refactors that I've found are the Samyang/Rokinon 135mm f2 which I think I would get used, and the Askar fma 180 (which I haven't been able to find anywhere actually, lmk where I could get this if you suggest it please). My main targets as of right now are the bigger dso's like Orion, Andromeda, Pleiades, etc.

On the one hand, I would think the Askar would be better for the slightly larger focal length which would get better framing on my objects, but on the other, the 135mm is f2 vs f4.5. Which do I choose? or if you know of a better option, let me know!

Thanks!

[Icesheet]

I’ve had both and used both on a Nikon D600 but not at the same time unfortunately so can’t give you an objective comparison. 
 

The short answer is you probably can’t go wrong with either. Personally I have had a better time with the Askar. The stars have been much better in the corners than what I had with the Samyang. Although I may have just had a bad copy of the lens. The other factor that puts the Askar ahead of the Samyang for me is the versatility. It acts as an astrograph, guide scope and spotter and is good at them all. It does seem the Askar may have some blue bloat but easily solved with a filter.
 

Of course the biggest advantage of the Samyang is you can image wide open at F2. There’s nothing else at that price that can do that.  
 

As I say you can’t go wrong. Just buy from somewhere with a good return policy 👍🏻