[Na Horuk]

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Can we think of a better lens for the job?

Samyang 14mm and Samyang 24mm f1.4 are ultra wide with very fast aperture and low coma; great for astrophoto. But manual focus, and you should buy them with warranty in case you get a decentered lens and need to return it.
Maybe the Venus 15mm or Irix.. quite a few ultra wide options out there now. But most of them are manual focus. I don't know how good they are regarding coma and edge sharpness. But I originally mentioned lenses that are similar to what OP asked about. Still, something like Samyang 14mm or 24mm would be good for astrophoto and its really really wide. And still quite affordable.
I mentioned my three lens kit earlier. Usually I have Samyang 14mm on the wide end, then DA 35mm or DA 40mm XS as the normal (ASPC), plus DFA 100mm.

[pres589]

Maybe we should get an idea of budget available for this from the OP before this goes much further. The DA 35 f2.4 is, what, $150 new? $125? Is that an issue? Only they can tell.

[UncleVanya]

Nikon Lenses will work on Pentax without modification if they are pre-AI - they don't lock but on a small light lens that's not an issue. They will likely reach infinity before it says infinity on the lens since the mount on Pentax has a slightly shorter lens to focal plane distance. The Nikon 24 f/2.8 shown here is not a lens I'm familiar with but it is one that has a reasonable reputation. (I have no relationship to this sale.)

Nikon NIKKOR JAA110AC 24mm f/2.8 Non-Ai Lens | eBay

[FantasticMrFox]

I didn't suggest it due to poor edge performance on full frame (from everything I've heard, and I believe Adam the admin has stated that he doesn't really consider it a true full frame lens due to these issues) ...

Oddly enough, poor sharpness is not something I've ever heard or read about with this lens. In fact, Photozone wrote that "Its primary strength is an extremely high resolution across the image frame combined with minimal CAs. There're few if any lenses which can rival the Samyang here which is nothing short of sensational for such an low cost product ..." ePhotozine writes: "Excellent sharpness in the centre at f/2.8 and across the frame when stopped down to f/5.6 or beyond"

The issue one mainly reads about is a wavy distortion pattern that makes it unsuitable for architectural photography, but can be fixed to an extent that it's perfectly fine for landscapes.

[pres589]

I would be buying this myself right now if I wasn't about to move to another state. And it fits on the camera properly and has autofocus and is said to be quite good on full frame. For about the price of a DA 35 f2.4;

Sigma 24mm f/2.8 Super Wide II for Pentax [Excellent+] Free Shipping From Japan | eBay

Fox: Maybe Adam will see this thread and comment. I've no full frame camera or Sammy 14's to test so I can't say for myself. I may also be mis-remembering so grain of salt.

[mikesbike]

A wider angle would seem more appropriate, but on a FF body you do still get wide angle with 35mm. I would recommend the FA 35mm f/2, which is made for FF use. The FA 31mm f/1.8 Limited would be even better, but more costly, since you are getting into the absolute premium range of quality. Otherwise, if you can find a good FA 28mm f/2.8 it does quite well even wide open.

[awscreo]

A lot of ASTRO guys seem to swear by Samyang/Rokinon 24 1.4, a lot faster, sharp wide open, will gather a lot of light with that aperture and isn't too expensive. I'm planning to get one myself for next summer.

[normhead]

And, i do have an old manual focus, no auto Tamron 28mm F2.5 lens. I think this may not be ideal because since there is no A setting, it will be wide open and may not be as sharp as it could be.

Focus, stop your lens down manually, shoot in AV, everything will be hunky dory.

[cyberjunkie]

Focus, stop your lens down manually, shoot in AV, everything will be hunky dory.

It depends on which Adaptall-2 ring is mounted. If it's M42 you can use it the way @normhead has suggested. If it's a PK adapter you can go the "green button" way (plenty of references on this forum). If you have a P/KA adapter leave the diaphragm ring on A and use any exposure mode you like.
Both the Tamron Adaptall-2 24mm and 28mm are still very usable, and should work more than fine at medium diaphragms. I suggest to buy a P/KA adapter if you find a decently priced one.
All Adaptall-2 lenses you may acquire in the future would work as Pentax-A objectives (well, almost).
The only weak spot is the BBAR multicoating. Contemporary T* and SMC were much better!
With wide angles flare can be problematic.
Almost contemporary 17mm and 2.5/180mm "Anniversary", two lenses I routinely use, are very different under this point of view. The latter gives very little flare problems, while the former is a pain to use in low light, with artificial light sources within, or just outside the frame.
The Bower/Samyang 14mm, albeit wider, needs less care in the composition of the picture. Btw, apart from geometric distortion, it works just fine on my K-1. There are even Lightroom correction profiles, if needed...

Cheers

Paolo

[JensE]

On a recent trip to Lofoten, I used the following on a K-1:

1. Samyang 12mm f/2.8 fish-eye - the lens I bought before this trip. This gives you enough angle for shots covering a large portion of the sky, without the extreme size compression of a classic fish-eye like the Zenitar mentioned above. By now prices have come down a bit since introduction. A very sharp lens with very little coma even wide open. I like fish-eyes also during the day, with its flare resistence I'am very happy with this lens. Absolutely recommended for your trip. An example:


And another: No way to capture those structures with anything less than 180 diagonal coverage:

Much less moonlight here, so I'm struggling with orange Sodium streetlights in the foreground.

2. Voigtländer 20mm f/3.5: Definitely not corner-sharp wide open (just center), nor very fast, but my widest rectangular choice. Some nice shots with ~10s @ f/3.5. So do give your 25mm, stepped down a bit, a try at home in the night sky and see how it behaves! Btw., no A-setting needed. Expose in M, ISO set to 800 and do the rest in post-processing. Check moon phases and look for similar light before your trip to try!

2. F28/2.8. Not ideal wide open because of clearly visible coma in the corners. Not so bad as to become distracting for aurora shots, but not great for "starscapes". The angle of view is useful for shots of landscape features "under aurora lights", i.e. when focusing on certain patterns in the sky with landscape context.

3. F50/1.7 @2.0. Sharp and fast, narrowing down even further. Was useful e.g. to photograph lights over the somewhat solitary mountain on the right in the fish-eye picture, again in full moon:


I'll add more samples once I get around to scale/upload them - likely for posting in other threads.

How fast of a lens do you need? In general it is of course the usual trade-off between shutter speed, noise and depth-of-field. I found 4s to 8s at f/2.8 to give very satisfactory results for medium-strong lights (I think we had a max. Kp of ~5, often not more than 3) noise-wise. You can see that the above 4s exposure still retains a good structure at the far right, where the movement happened. Occasionally, I wished I could have gone faster when lights moved quickly, a (badly composed) shot with the F50/1.7 at 2s turned out a little crisper. On the other hand, under almost full moonlight, you get a nice landscape balance with the 12mm@2.8 without having to combine exposures in post-processing, i.e. the above was a single exposure. So if you find a 24mm/1.4, it will be excellent in giving you options. But you may wish for a wider view occasionally as you'll be similarly far under the lights oval.

[Scorpio71GR]

I would not worry about the DA 35 on the K-1. Just stop it down and you will be fine.

DA35 on the K-1 @ f11.

[JensE]

Just noticed the above was actually taken with 2s exposure, therefore the well-captured structure on the right. I quickly checked some 50mm shots: good noise-wise with 1s @ 2.0.

[repaap]

Another nod for wider lenses. I have sammy 14/2.8. I have not yet used it in auroras with my K-1, because they are not so common at where I live but next winter perhaps..it won’t help you thou..generally you would like a scenery part of picture and lights often loon from horizon to above you. So in FF terms atleast 24 mm is really good. I’v used DA*16-50 and sammy with my K-1 for auroras, sammy was better. And MF is needed. So AF would not matter.

Just my thoughts, and experienses. Also good tripod with good tilting head will be handy. Just in case you wondered. Exposures will be around 2-8 seconds.

[peggers]

Thank you all for your replies. To your replies I have a few more questions

Works great! There is some vignetting at f/2.4, but it's easily corrected in post, and above that is gone.

And also Adam. If F2.4 causes some vignetting, would F4 suffice?

Does the Tamron have an aperture ring? If yes, you can still use any aperture you want. You just have to set it by hand and use M mode with fixed ISO (not Auto ISO, not ISO range). A setting on aperture ring means the camera can set the aperture. Menu --> Enable aperture ring (very end of menus), and then M mode with fixed ISO. All other modes will default to "Av mode" which will only shoot wide open aperture. you can see if camera switched to Av mode on the back LCD

To Na Horuk. Great tip! Yes it does have an aperture ring, and yes using manual and changing the aperture works too. This gets around the issue of it being not so sharp at F2.5. So I will be able to use F4 I think and get good results. I will have to venture outdoors at night before I go to suss this out. And yes, I did see the thread you initiated and really learnt a lot from the replies (What a great forum this is!) The difference between my question and yours was the camera body. By the way, did you ever publish your Northern lights shots? And do you recall what your exposure settings were?

I took this with the 35mm f/2.4 and the K-1 -- Apart from not being as wide as you might need, it should work fine for some night sky shots

To Enoeske, that is a great shot, and I do note you used the lens I was inquiring about.

That Tamron 28mm might do the job if you can stop down a bit and still get the shot. A Zenitar 16mm fisheye is about amount of cost and seem pretty decent if you can stop down. A DA 18-55 WR is easy to find for $100 used and is said to work well on full frame if the zoomed focal length is kept to about 24mm or longer. There have been some different 24mm lenses over the years available in k-mount and m42 what would probably work quite well. I like the idea of the FA*24 but they're non-cheap.

To PRES589, I'm thinking you might be right about the Tamron. And in other news it turns out I already own a DA 18-55. It was the kit lens that came with my K5. I had dismissed it because of severe vignetting, but hadn't considered using it at 24mm and up. Definitely worth a try. And, yes! The Northern lights do sound awesome. Been on my bucket list for a while

The Irix 15mm f/2.4 should be a pretty good alternative as well.

I had a look at this online. Seems like a very nice lens, and very happy it is $200 cheaper than equivalent Nikon/Canon lenses, but is a bit outside my budget.

At the end of the day, I may still purchase the DA 35mm from Pentax Australia next time they have a 15% off sale. In the meantime, I will have to experiment with what i already have