Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

20mm options for a7s 4K timelapse: Sigma Vs Rokinon Vs Viltrox

  • Please log in to reply
6 replies to this topic

#1 Nicoloks

Nicoloks

    Lift Off

  • -----
  • topic starter
  • Posts: 2
  • Joined: 19 Aug 2019

Posted 19 August 2019 - 11:59 PM

Hi All,

 

Really just getting into astro on a limited budget and have made the first step by purchasing a used Sony a7s. I'll primarily be looking to create time lapse and even hyper lapse 4k video of the milky way, so basically short exposure wide field of view night shots with the lens likely being used at wide open aperture. Given the a7s is only 12MP there is not a great amount of head room for down sampling to 4k video, as such I think the 20mm focal length will give me the best balance between field of view, image compression and light gathering capability. I am looking to get a one lens fits all for the foreseeable future until my bank balance recovers, otherwise I'd probably just go with the 14mm f/2.8 & 24 f/1.4 combo. Also, given I will not be doing a whole lot of stills, I think at this stage my preference is light gathering capability as being more important than putting up with moderate undesirable lens characteristics. 

 

Anyway, given the above use case I would really appreciate any feedback on the following (I have been using a GH5 with Laowa 7.5mm f/2 for reference);

  •     Sigma 20mm f/1.4 - I've noticed there are quite a few used options in my area of this lens (usually Nikon mount) which are selling for as little as a hundred dollars more than new copies of the other two lenses I'm looking at. I've looked at astro centric reviews for this lens and people seem to either trash it or love it with the caveat they acknowledge it has some coma issues. Given 95% of the content I'll be producing is 4k video, would this low res (compared to stills at least) requirement lessen the visual impact of coma in favor of the Sigma's increased light gathering capability? This lens alone would give me nearly a 3 ⅓ stop advantage over what I am using now (using NPF rule for exposure time). Given this lens costs close to double the other two when new, I'd only really be considering this option if I could source a good used copy fairly cheaply.
  •     Rokinon / Samyang / etc 20mm f/1.8 - This seems to be the gold standard for this focal length. On a good copy the coma is supposed to be best in class, however wondering as to the build quality / quality control as I've read a few claims that you may need to return this lens a few times to get a good one. Used ones do come up, but never seem to go for a huge amount less than new, in which case I'd likely look to purchase new so I have the option to return if it is a dud.
  •     Viltrox 20mm f/1.8 - A newer mirrorless only lens, Dustin Abbot and a few other reviewers seem to give it a solid rating. The 14 aperture blades vs 7 of the Rokinon should give stars a nice round bokeh when throwing the sky out to focus on a near object. Vignetting is supposed to be less than the Rokinon, but the coma is not as well controlled. Both these f/1.8 options would give me a 2 ⅓ stop advantage from the lens alone over what I am using now. Being newly released I've not scene any used options, so this would need to be a purchased new also.

Really appreciate any feedback comments or advise. Thanks.



#2 Jim Waters

Jim Waters

    Mercury-Atlas

  • *****
  • Posts: 2790
  • Joined: 21 Oct 2007
  • Loc: Phoenix, AZ USA

Posted 20 August 2019 - 12:14 AM

  • Rokinon / Samyang / etc 20mm f/1.8 - This seems to be the gold standard for this focal length. On a good copy the coma is supposed to be best in class, however wondering as to the build quality / quality control as I've read a few claims that you may need to return this lens a few times to get a good one. Used ones do come up, but never seem to go for a huge amount less than new, in which case I'd likely look to purchase new so I have the option to return if it is a dud.

Really appreciate any feedback comments or advise. Thanks.

IMHO Rokinon lens below 35mm suffer from quality control / manufacturing problems and maybe design problems.  I had a 24mm and 16mm that had very bad coma, inconsistent edge distortion and focus problems.  I returned both of them.  I have switched to Sigma ART lens.  Yes - they are ~2x the cost but I can shoot wide-open.

 

EDIT - Its been some time but I think I was shooting at f/2.8 to 3.2.


Edited by Jim Waters, 20 August 2019 - 12:34 AM.


#3 GunArm

GunArm

    Lift Off

  • -----
  • Posts: 20
  • Joined: 16 Jul 2018
  • Loc: North Texas

Posted 20 August 2019 - 12:23 AM

My experience with Rokinon https://www.cloudyni...t/#entry9517592



#4 Jim Waters

Jim Waters

    Mercury-Atlas

  • *****
  • Posts: 2790
  • Joined: 21 Oct 2007
  • Loc: Phoenix, AZ USA

Posted 20 August 2019 - 12:26 AM

Can you rent a lens and try it out first?


  • t_image likes this

#5 Nicoloks

Nicoloks

    Lift Off

  • -----
  • topic starter
  • Posts: 2
  • Joined: 19 Aug 2019

Posted 20 August 2019 - 01:19 AM

Wow, that goes a long way to firming up my hesitations towards going for the Rokinon option. Unfortunately living in a rural area I don't have a great deal of rental options locally. The only place I've found locally doing rentals with the Sigma (not the Rokinon or Viltrox however) has a minimum 6 month rental term over which time I would end up paying for close to a third of the cost of purchasing the lens outright. I'm thinking if I get the Viltrox straight up I will always be wondering how much better the Sigma is for light gathering. Approach might be to get the Sigma and see if the image artifacts at wide open are something I can put up with. If not, sell it and then take a look at the Viltrox. I already have a Nikon -> Sony adapter, so I could pick up one of the Nikon mount versions of the Sigma I know are for sale in my area and be on my way. 

 

Thanks for the input regarding the Rokinon option, glad my gut feeling wasn't too far off the mark there.



#6 Sven_Bortle5

Sven_Bortle5

    Explorer 1

  • -----
  • Posts: 64
  • Joined: 08 Feb 2019
  • Loc: Düsseldorf, Germany

Posted 30 August 2019 - 02:30 AM

Don‘t know if this is available for you, but I have made good experiences with the IRIX 15mm on my Canon 70D.

 

Wanted to try it on the Milky Way in Denmark this week, but a neighbor startet illuminating his house with 2 strong LED flooters. shocked.gif

 

Update: ... didn‘t find it for the Sony, sorry.


Edited by Sven_Bortle5, 30 August 2019 - 02:41 AM.


#7 gunny01

gunny01

    Surveyor 1

  • *****
  • Posts: 1682
  • Joined: 02 Jun 2014

Posted 30 August 2019 - 07:23 AM

  I've got the sigma 20mm f1.4 on sony a7iii.  Shooting stills of mw shows a lot of astigmatism in the corners.  I'm no expert, but there are plenty of write ups on this lens. 

 

  For indoor video, I really love this lens.  Shooting stills throughout a house, shows a lot of distortion.  So it's an ok lens for some things, but not worth the money imho.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics