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03-11-2015, 09:10 AM   #1
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Wide-field Astro choice (sigma options)

Hello!

As the milky way season is nearing I am planing to try some wide-field astro imaging. I have tried previously but it is not that simple with the FA 50 1.4. Something wider would be a lot better (especially on a APS-C sensor). So as I have my k500 and also the NEX 5N I think it is wise to go for a K mount lens(es) and use an adapter for the NEX. So I have been reading quite a bit and have come to a conclusion that Samyang (Rokinon) lenses are one way to go. Little coma, cheap, sharp, bright. I also have seen an opinion that they are very flimsy - inadequate QC, construction made of plastic and glue and that there is a chance that they will "fall apart" if I shake them a bit more roughly. Then there are old version SIGMA lenses - I am looking towards 28 mm F 1.8 EX - screw drive, but applicable to FF The new version of 30 mm 1.4 art also looks appealing, but then again it is APS-C lens but has HSM. The 35 mm art version is FF but it is considerably pricier and I don't consider it to be "wide" - especially on a APS-C. Ok sigma has the brand NEW 24 mm ART version which is really really what I would like to get if it had a compatibility with pentax but it doesn't. Ok, there are some statements that due to upcoming FF pentax, sigma is planing to re-release some of their lenses also for K-mount. When? So All I wanted to say is that I am lost .
So I have the options:
1) Samyang 14 mm F 2.8 (compatible with FF)
2) Samyang 16 mm F 2.0 (compatible only with APS-C)
3) Samyang 12mm F 2.0 (only for NEX mount and for APS-C)
4) Sigma 28 mm F 1.8 EX (compatible with FF)
5) Sigma 30 mm 1.4 ART (APS-C)
6) Sigma 35 mm ART (FF, but I don't think it is a good idea considering the focal length).
7) Sigma 24 mm ART (Hypothetically if and WHEN it becomes available for pentax)

So can you please share your experience, opinion, knowledge. Obviously AF capability would be much appreciated as it would make these lenses more versatile. So yes - I am a bit lost here.

Please shed some light as I am sure there are other underwater rocks that I don't know about whereas some of you might.
Also a very serious question about SIGMA - is there a reliable info on which lenses they plan to re-release for pentax? So some info in this direction would be also very welcome.

Thank you!

03-11-2015, 10:00 AM   #2
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I only have experience with the Samyang 14mm (mine's the rebadged Bower version) from your list. I wouldn't call it "flimsy"; the mechanical construction feels solid and the focusing ring moves smoothly. The only QC problem I'm aware of is inconsistent placement of the infinity focus mark but there are articles on PF and youtube for adjusting it.

All of those Sigma lenses are long enough focal lengths where a 30 second exposure may show star trailing. Maybe add the Sigma 18-35 f1.8 to your list. That's a more flexible focal length for wide field astro. I've seen other PF users post nice results. The Sigma 18-35 is much more expensive than the Samyang 14mm, but is much more flexible if you want to use the lens for general non-astro photos.
03-11-2015, 10:15 AM   #3
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All of the Sigma non-art fast wide primes suffer from coma, so does my Sigma 20/1.8. It works but it's surely not as optimal as the Samyang ones for astro.
03-11-2015, 03:01 PM   #4
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If you are looking for astro, then look no further than the Samyang. I would get the 14mm especially since you will likely want to upgrade to FF one day. Also considering this, you may want to buy a cheaper older manual 24-28mm lens. I just bought a Sigma 28mm Mini Wide II and plan on using it for landscape, and astro.

03-11-2015, 04:31 PM   #5
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You gonna stick with apsc? the Rokinon 10mm2.8 is what I will be purchasing for that. There is a guy named Kevin Palmer who has taken some really nice night photos with that.
03-12-2015, 01:09 AM   #6
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Original Poster
Hi!

Thanks for the info - I had not checked the aberration aspect of Sigma 20-28 mm 1.8 EX series. Somewhere I saw info that particularly 28 mm version was astro worthy but then again that was before some 8 years.
About FF...sure I am interested getting into FF but I don't know weather it will be the PENTAX or maybe sony mirror-less. I think there is no need for me to do an immediate upgrade. For the stuff I do, my K500 is more than sufficient. Secretly I am waiting for a global-shutter CMOS to hit the consumer market. So yes - FF is planned, I just don't know when. I know that I won't quit using APS-C pentax. I have quite a lot of glass and I am not willing to render them useless.

I almost have made my choice - I think to to go for a CROP Samyang 16 F2. I think 2mm sacrifice (in respect to FF 14 F2.8) is worth an extra F stop.

I have seen this imprecise infinity mark issue - this is seen not only on samyang. Some of my sigmas also have this - that is not that big of a deal. What bothers me is the well documented lens decentering problem which is not that apparent for casual photography but becomes noticable in star imaging. Maybe only the bad word gets out on the web but I have seen this decentering issue mention in several sources.
05-08-2016, 08:35 PM   #7
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Hi, I am resurrecting this thread because I am having the same kind of questionning lately...
have you considered the Rokinon 24mm F1.4 ?
it seems to have very good reviews and it has 2 more stops and is FF: Best Lenses for Milky Way Photography: Canon Astrophotographers – Lonely Speck


anyone has tried it on Pentax ?


and mor recently, Pentax has issued a new DFA 15-30 f2.8... I think it's too early to have any reviews related to astrophotography.. but since it's a zoom, may also suffer from coma aberrations...
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