[LukeOB]

I am getting a lot of use out of my trusty old DA 12-24, at 18mm. And of course i can still use all my filters. I have the 14mm Samyang but find the distortion really detracts from the landscapes. Good for astro though. The Laowa 12mm has only just caught my attention and that is most likely going to be my next purchase.

[Storm Chaser]

I have a Samyang 14mm F/2.8 but a bad copy, if you get a good one should be ok with some post work. Been looking at the Irix 15mm F/2.4 it has a lot of features I like, and build quality looks very good as well.

Brian

[Bob 256]

I lucked out and got a Vivitar 14mm Series 1 lens just after I purchased my K-1 a few months back. It's manual focus but I can live with that. It's very sharp and you can zoom in almost to the pixel-peeping range and think you're seeing an un-enlarged shot from a mediocre lens. Unfortunately, I don't think you can get a Vivitar in the K-mount now. Other brands are available, but I've heard those are slightly different although they look almost identical to the Vivitar though the knock-offs are said to be pretty good image wise - just not as consistent lens-to-lens. You might keep your eyes open though, and see if a Vivitar pops up. They are still available on ebay - just not in the K mount.

[Medex]

Ultra wide is often considered to be wider than 24mm nowadays.


If its stopped down landscape work, I'd recommend the following :
1. K28/3.5
2. Samyang 14/2.8
3. Irix 15/2.8
4. FA31ltd


The Samyang 14 is a steal if you can do with the distortion (which can be heavily reduced with a lens correction profile).
For the price you can get it, you can easily spend a bit on a filter system for it.
Its basically the IQ on par with most of the UWA out there that are 3x or more its price (win some lose some on other factors)


There are others of course like the Laowa 12mm, Samyang 20 and 24mm, but I have not used these to safely say that they are good.

Fa31 is ok for landscapes but in case of astrophotography is is not due to astigmatsm on the peripheral part of lens.

[Kerrowdown]

Ultra-wide prime for full frame

I'm quite pleased with how my "Good Lady” (Pentax-A 20mm F2.8) performs on the K1.

[texandrews]

I have a Samyang 14mm F/2.8 but a bad copy, if you get a good one should be ok with some post work. Been looking at the Irix 15mm F/2.4 it has a lot of features I like, and build quality looks very good as well.

Brian

Just got the Irix 15. Very pleased so far, build quality of the Blackstone version is excellent. Simple, low and easy to correct distortion---so, just what I needed for interiors and my museum installation documentation work. Seeing no CA or other problems as of yet. Sharpness seems fine. Occasionally a challenge to focus, to be expected with a manual lens this wide. Nice DOF indicators and a hyperfocal marker, plus a user adjustable infinity adjustment on the lens, very nice touch. Chunky, but compact, rather like the K1.

[cqua77]

If you can find it Zeiss 21mm or 18mm (I searched during 2 years before finding one of them).

More easily findable Zeiss 25mm.

Cheaper option Voigtlander 20mm (you can find it on pk mount in some asian sites)

---------- Post added 12-17-17 at 12:42 PM ----------

I'm quite pleased with how my "Good Lady” (Pentax-A 20mm F2.8) performs on the K1.

Your list of Pentax A lenses is just impressive.