Jump to content


Orion 120ST EQ review

  • Please log in to reply
4 replies to this topic

#1 Olivier Biot

Olivier Biot


  • *****
  • Posts: 24946
  • Joined: 25 Apr 2005
  • Loc: 51°N (Belgium)

Posted 20 September 2011 - 03:19 PM

Orion 120ST EQ review

By Ed Wawrzaszek

#2 gmartin02


    Viking 1

  • *****
  • Posts: 861
  • Joined: 11 Apr 2005
  • Loc: Santa Clarita, CA

Posted 22 September 2011 - 02:06 AM


I am glad you are enjoying your 120ST. I also just purchased a used one for an unbelievable price from an Astromarter. The front of the objective was really dirty & it was missing the dew cap (and had a spider web inside the OTA and a living spider in front of the objective inside the dew shield - it was stored in a garage for many years.) I disassembled everything (except for the lens cell), cleaned it all up, including the front side of the front lens of the objective & the rear side of the rear lens of the objective. The optics turned out to be absolutely pristine after cleaning, and the rest of the scope cleaned up nicely too. I ordered a replacement dew cap from Orion to keep the objective protected, and it is now ready for observing.

I really love using a fast refractor - it doesn't have the light gathering of my C11, or the top notch optics of my Tasco 10TE or my Intes MK-67 Deluxe, but it fills a gap in my viewing because of the much shorter focal length. Being so light, it is really easy to set up & use, and it has much wider field views than my other scopes. It is really nice to look at the Eastern Veil nebula with an oiii filter and see the whole loop instead of just portions of it. It is also great for open clusters.

Someday I would love to have an APO refractor, but in the mean time the ST120 fulfills a valuable role in my visual observing. The next step is to get field flattener for it & try some deep sky astrophography with my Canon T2i.


#3 StarStuff1



  • *****
  • Posts: 3891
  • Joined: 01 Apr 2007
  • Loc: South of the Mason-Dixon Line

Posted 22 September 2011 - 12:19 PM

A few years ago I purchased a used ST 120. I was pleasantly surprised at the low amount of CA (false color) present when viewing the Moon and other bright objects. It was so low I became suspicious and measured the exit pupil with a low power eyepiece. Hmmm, the objective was noticeably stopped down by something. I pulled the focuser off thinking a baffle was mis-placed. However it turned out the focuser tube was too long and interferred with the light path. I cut about 1 1/2 or so inches off the front end of the focuser tube. The result was more CA but a brighter image and increased resolution, especially on DSOs.

A vendor at a star party told me that the factory used the same focuser on both the 120 f/5s and the 120 f/8s. If you have a ST120 you might want to check yours for vignetting of the objective.

#4 CollinofAlabama



  • *****
  • Posts: 2198
  • Joined: 24 Nov 2003
  • Loc: Lubbock, Texas, USA

Posted 27 September 2011 - 09:15 PM

Well, the author writing he doesn't see any CA, even on bright objects is clearly very insensitive to this aberration. I owned the Orion 100mm F/6, and even though detail on the crescent moon was very good, the blatant purple stamping around gray-white Luna was strikingly unwelcome. But it was a razor sharp scope.

This past Saturday night I joined a group at the Muleshoe Wildlife Refuge, basically in the middle of nothing, 60+ miles out of town. I had my Orion 100mm ED F/9 on the AZ-4, without any wind, the tripod legs completely extended. Someone found Delta Cephei, amongst the Messiers and NGCs. The separation and color in mine were nice, but a friend's 120ST showed distinctly better color variation -- aperture rules, folks. I wouldn't have tried my 7mm T6 on Jupiter in the 120ST like my 100mm ED, but the 120ST's a GREAT scope, provided one use it for what it's designed, brighter galaxies, nice doubles, star clusters, and other faint fuzzies. It may make you blue (deep indigo, in fact) on the moon and brighter planets, it may turn tight binaries to mush, but for Delta Cephei, M31-32-110, M33, M35-38 and the like -- look out!

#5 Norman Sullivan

Norman Sullivan

    Lift Off

  • -----
  • Posts: 8
  • Joined: 20 Nov 2014

Posted 21 November 2014 - 05:37 PM

I was able to buy this model about 5 years ago.  It was used, but in excellent condition, and the price was right.  At the time, I also had an Orion 6" Dobsonian, so it was natural enough to compare the two.

Right off the bat it was evident that the 120ST was the sharper of the two, and I could always achieve a good focus.  Though fast, the short refractor did a better job on double stars.  

The surprise was that it seemed to do equally as well as the 6" on DSOs - perhaps attributable to the local light pollution.  What was no surprise was that it was easier to manipulate, set-up, and carry.  

I subsequently sold the Dob. and put the proceeds towards a Vixen Porta mount.  This was as big a step as going to the RFT to begin with.  The Porta is more than adequate for the ST and I prefer the alt-az style mount.  BTW, Orion sells a special color-fringe filter for fast RFTs, it does help, I use it for 90% of my observing.

This is not the instrument to go hunting Stephan's Quintet, but for general observation, including high power views of the moon, Jupiter, double stars as well as most DSOs, it gives a good account of itself, especially in light of its reasonable acquisition cost.  

Someday perhaps, if my ship comes in, there may be a Teleview or Astro-Physics, but until that time the 120ST will serve just fine.

Edited by Norman Sullivan, 21 November 2014 - 05:39 PM.

Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics