The Rokinon/Samyang 14mm's are decently sharp, maybe even really sharp. The biggest issue with them is 75% of them come De-centered. Which means that when you focus, typically 2 of the corners will be super soft as they are so out of focus because the glass is not parallel and one of them was assembled at an angle. It's been going on for well over 15, maybe 20 years. And Rokinon doesn't seem to care, because as I said it's been going on for many, many years.
I have bought probably 15 or 16 of the Rokinon 14mm lenses, because initially it was for a primary MW lens for my camera years ago, and I have kept them as backups or primary lenses once I got multiple camera bodies at night. And each time when I needed a new 14mm, and I would order one. The first one I got was always decentered, and it would typically take returning the bad lens, and getting another new lens to test 2 or 3 times before I finally would get a good copy.
My worst case was I had a good copy, and the optics shifted inside and it became a bad copy. But sadly I found out about it at the worst time. I had gone up to Glacier NP and it was the last year before the Park Rangers totally closed off the hanging valley where Triple Falls is located. I had spent the night capturing the MW there. When I got back home I found that while the image was focused and the stars were sharp in the center and right side. That the upper left side the stars were horrible out of focus. It took me days to piece together a workable image from it where I was lucky enough to have found a few images where the upper left was just a bit out of focus and I could over sharpen that area and then blend it into the original image that was sharp except for the upper left.
So that experience burned me pretty well. I have bought some Rokinon 14mm's since for backups as there really hasn't been until recently any other inexpensive fast 14mm. But again, always with having to test the lenses, and return the bad copies many times. I have even tried their Mark II version which has a locking mechanism for the focus which is a cool feature. But it too was decentered on my initial copy.
Sorry.... probably too much info there...
The Laowa 15mm, I think Kyle had tried? Someone here has. It's biggest issue is Coma in the corners if I recall.
As to other ones. The best one out there by far is the Sigma 14mm f1.8/f1.4. Sigma years later still can't keep up with the demand for this lens as it's the Cadillac of all night time lenses. It comes with a hefty price, and I haven't been able to keep up with the Canon lens mount changes, but they may not make it for your camera, you will have to check. Maybe you can use a lens adapter. But bear in mind it's going to cost from $1500 to $1900 depending on the version and model number. But there is no better MW lens out there. I have both versions, the f1.4 isn't made in a Nikon mount, so I had to buy a Sony version and then get the adapter from Sony to Nikon Z mount.
A cheaper alternative that is out there is the Viltrox 16mm f1.8. It is super sharp, it's f1.8 and it is only around $500, sometimes less during sales. One of it's coolest features is that it has a display on the lens itself. As you know focusing at night can be a pain. And as opposed to the old days, inifinity on a lens today isn't really always true infinity. But with the Vitrox (which is permanently mounted to a Nikon Z6II) all I have to do when I turn it on at night is turn the display to say the distance is between 19 and 30 feet, and everything from ground to stars is in focus for me. With the new Focus by Wire of the mirrorless cameras, you can't tape a lens focus ring like with a manual focus, and there are few manual focus lenses for the mirrorless compared to the old days, most seem to be AF lens.
So if it was me, and you didn't want to spend a fortune since you are just starting to get into MW photography I would get a Viltrox 16mm f1.8.
But if you know you really want to capture the MW on a regular basis, then spend the extra money and get a Sigma 14mm f1.8 or f1.4. The nice thing with the f1.8 is you can tape the lens focus ring once you find where you want your focus to be and your images will always be sharp. The f1.4 version is a Focus by Wire model, so every time you turn on the camera, the lens will need to be focused again. The f1.4 version does have a Focus Lock switch, but it only locks the focus as long as the camera is turned on. Turn off the camera and the lens loses power, and the lock doesn't work. A really bad design with good intentions from Sigma.
As to night time photography, the difference between f1.8 and f2.8 is almost like night and day. If you shot with a f4 lens at night and then moved to a f2.8 you would know it was a huge difference that was. Well, going to f1.8 or f1.4 is like night and day different. So much more light gets into the sensor, the night sky pops in your image compared to f2.8 lenses.
