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04-10-2014, 10:58 AM   #1
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How to decide UWA lens for astrophotography, landscape, architecture, indoor?

Hi all,

I have trouble deciding which UWA lens to buy. I plan to use the lens for a variety of purposes including:

* Astrophotography
* Indoor and possible low light
* Landscape / architecture
* Special uses - view from helicopter

I have the following lenses in sight:
* Pentax DA 15mm F/4 (SMC for starburst effect, HD because it's easier to get)
* Pentax SMC DA 14mm F/2.8
* Rokinon 14mm F/2.8
* Rokinon 16mm F/2.0

I am primarily looking at build and optical quality.

For astrophotography / low light it's important to get many photons. Thus a low F number is preferable. The lens should also be resistent against coma abberation. For landscape / architecture the lense should be flare resistant.

Reviews seems to favor the Rokinon 14mm F/2.8 or 16mm F/2.0 because it features an aspherical lense which reduces coma abberations. Sharpness should be good, but there is some concern about QC on the Rokinon / Samyang lenses?

How does the Pentax 14mm feature in respect to coma abberations? Does it have an aspherical lense?

Which one would you recommend?

Best regards,
Michael

04-10-2014, 12:04 PM   #2
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Hi Michael!

I recently got the DA14. It seems to be more flare resistant than my Sigma EX 15-30. I do not notice cromatic aberrations, nor do anyone else in the review section: SMC Pentax-DA 14mm F2.8 ED [IF] Reviews - DA Prime Lenses - Pentax Lens Reviews & Lens Database

The DA15ltd is smaller but a stop slower. Compared to the Rokinon (or Samyang) you gain autofocus, but have no aperture ring.
I was lucky to get mine for a reasonable price, it seems to go for over $700 currently.

Seb
04-10-2014, 01:00 PM   #3
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Hello Michael,

I was in your shoes about a month ago and I pulled the trigger on a Samyang 16 / 2.0 . The first copy had decentered optics which showed up as uneven vignetting and coma in one corner. I had to send back. I received another copy within a few weeks and it was a much better copy, although not perfect. I am going to keep it as it is likely the best possible. There is a time to hold em, and a tile to fold 'em.

The Samyang 16 will vignette at f/2 by a moderate amount, but is perhaps perfect at f/2.8 and beyond. F/4 does seem to hold the corners a bit more of course. Coma is still noticeable in the extreme corners at f/3.2 and under. Here is a full resolution .jpg from my K-5 IIs.

70 seconds f/3.2 tracked exposure: https://dl.dropboxusercontent.com/u/59003880/IMGP0860.jpg SIZE: 13.6 MB

The rendering is beautiful, but coma still an issue. I'm going to keep it as the coma is not a show stopper for much other work I plan on using the lens for. Your copy might not be as bad, or it may be worse, as my first copy was.

Coma was not much worse at f/2. The vignetting could be modeled and removed from the frames producing great images in very short exposures, albeit not perfect. The price is right.

Focus can be tricky wide open, but it is very sharp at the center at full aperture and is superb full frame at f/5.6-f11 with f/16 very usable with great DOF.

Good luck.

Jim
04-10-2014, 01:21 PM   #4
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I have the Rokinon 14 and 8 fish eye. They are great but sometimes it would be nice to have auto focus. I also had to adjust the focussing ring which was easy.

04-10-2014, 02:02 PM   #5
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Thanks for all the great feedback!

I am leaning towards the DA 14mm because I can currently get it for about the same price as the Samyang 14/16mm in Denmark. It weighs a bit less than the 14/16mm Samyang and hopefully Pentax has better QC, and it still has options for a 77mm filter.

The only concern I have is with respect to coma aberations. As I understand it the lense does not feature an aspherical element, which would help to reduce coma aberations.
Samyang 14 mm f/2.8 ED AS IF UMC review - Coma and astigmatism - Lenstip.com (Samyang 14mm good control of coma aberation)

Here is the same test for the Pentax 15mm:
Pentax smc DA 15 mm f/4 ED AL Limited review - Coma, astigmatism and bokeh - Lenstip.com (acceptable coma control at f/5.6)

Unfortunately I can't find a test for the DA 14mm but an educated guess would be that I would have to stop down to at least f/4.0 to get a reasonable coma control if used for astrophotography.

Bassek - have you tried to do a test wide open or at f/4.0 to determine center vs corner coma aberations?
04-10-2014, 02:38 PM   #6
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If I calculated correctly, the 14mm lens at f/2.8 has a hyperfocal distance of 3.5meters. So it shouldn't be that hard to use when focusing manually!
04-10-2014, 03:08 PM   #7
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QuoteOriginally posted by mln83 Quote
I am leaning towards the DA 14mm because I can currently get it for about the same price as the Samyang 14/16mm in Denmark. It weighs a bit less than the 14/16mm Samyang and hopefully Pentax has better QC, and it still has options for a 77mm filter. The only concern I have is with respect to coma aberations. As I understand it the lense does not feature an aspherical element, which would help to reduce coma aberations.
If you visit the Astrophotography Group, you can see a single DA 14 astrophoto by smigol here:

https://www.pentaxforums.com/forums/groups/135-astrophotography/3103-samyang-...#gmessage39914

And you should also take a look at nightfly's samyang pictures in the 'Astrophotography' thread here:

https://www.pentaxforums.com/forums/6-pentax-dslr-discussion/113178-astrophot...ml#post2768008

I doubt that you will ever find a truly coma-free (consumer) wide angle lens when it comes to 100% views of images of point-like sources of light near the corners. After all, these lenses were optimized for other purposes.

Last edited by Stone G.; 04-10-2014 at 03:12 PM. Reason: links added
04-10-2014, 03:17 PM   #8
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Maybe someone with more experience than me can answer this but from my limited knowledge of astrophotography it seems like you usually use a long exposure time (a bare minimum of 60 seconds but usually 200+) at this long of exposure time I don't think the difference between f2.8 and f4.0 is relevant.

QuoteOriginally posted by mln83 Quote
For astrophotography / low light it's important to get many photons. Thus a low F number is preferable.
Michael


04-10-2014, 03:19 PM   #9
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I would highly recommend the Samyang lenses. I have the 14mm. The only problems with Samyang are, as mentioned, QC problems (I also returned the first one, and the second one is not quite perfect, but meh) and miscalibrated focus scales (there are online tutorials on how to fix this. I didn't try yet, since I can't tell where the focus is until I pixel-peep).
The Samyang 14mm is often cited as a good astrophotography lens because it has low coma, its very wide angle (so you can have long exposure time), relatively fast (F2.8), and FF compatible (so it has little vignetting on crop cameras). Keep in mind that astrophotography is a difficult thing and requires a bit of skill and other tools (tripod, timer, software, possibly the OGPS thingy)

You can see my completely amateur astrophotography attempts with the Samyang 14mm here:
http://500px.com/photo/50888178
http://500px.com/photo/50888006
http://500px.com/photo/51610308
Only used tripod, in-camera dark frame reduction and 2sec timer, and Lightroom to process the raw files. No stacking, tracking, etc.

Last edited by Na Horuk; 04-10-2014 at 03:26 PM.
04-10-2014, 06:36 PM   #10
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On a side note DXO Mark just did a comparson with the Samy 16mm f/2 going up against Canon and Zeiss. Again, get a good copy.

Samyang 16mm f/2.0 ED AS UMC CS Vs Carl Zeiss Distagon T* 2.8/15 ZE Canon Vs Canon EF 14mm f/2.8L II USM: Superior uniformity - DxOMark
04-11-2014, 03:06 AM   #11
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Unfortunately I have shot less than 100 shots with my DA14 so far, not a single test shot, just "shots" in general.
The build quality is really good.

Here is a photozone review:

Pentax SMC-DA 14mm f/2.8 ED [IF] - Review / Test Report

Seb.
04-11-2014, 07:16 AM   #12
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I'm in the same boat as you. I'm looking at the same lenses you are plus the DA 12-24 and the Sigma 8-16. The Sigma 8-16 had reports of badly decentered copies. Since its not available in the USA anymore, that makes replacing it a much larger headache. The DA 12-24 looks very good.
04-25-2014, 05:27 PM   #13
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Thanks for all the great replies.

I decided to buy the Pentax DA 14mm f/2.8 mainly due to less weight (in comparison to Samyang 14mm/16mm), better QC and versatility (astro, landscape, indoor, special macro*ish - 0.17m focus).

Here are a few test shots of the night sky over Aarhus, Denmark. Lots of light pollution from the ~300.000 inhabitants in the city. Maybe I'll try to take the car out on the countryside to do more testing, but first impressions are good. Stellar coma aberration is present at the edge of the frame when shooting wide open. I do still feel that it's usable when you don't pixel peep, however when stopping down to f/4 it gets a lot better.
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