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So You Want to Buy a Big Refractor: My Decision, Setup, First Light and Beyond

Sky-Watcher Esprit 120ED Refractors Equipment
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Ryan Faulkner avatar
Ryan Faulkner avatar
I recently decided to add another scope to my fleet, gaggle, herd (whatever a group of telescopes is called). I have a William Optics GT71 with 0.8x focal reducer that I’m very happy with and a Celestron NexStar 8SE which is great for visual and planetary, but I’m still working on getting good images with it. With existing focal lengths of 335 (GT71 with reducer) & 2032/1280 (with .63 reducer) I figured a focal length in between would be a good addition. 

The announcement of the William Optics Pleiades 111 pushed me into researching the available options, which leads me to this thread.

While I love the aperture, speed and design of the Pleiades 111, I don’t think it’s a good value for the money (see my thread here). I turned my attention to other scopes in the ~500 focal length with a minimum aperture of 91 mm. I thought I had decided on the William Optics FLT91, because it felt like an upgrade, I could use my existing reducer and a flattener was available.

Then… the Sky-Watcher sale started. Scopes like the Esprit 100ED and Esprit 120ED were now in consideration, and I might as well look at the WO FLT120, since my budget mysteriously grew.


TLDR
With the massive savings (21%), included flattener and positive reputation I went with the Sky-Watcher Esprit 120ED.The goal of this thread is to provide information for others in a similar situation and hopefully pick up tips from anyone that has managed to read this far… 

My Equipment
Mounts
  • Pegasus NYX-101: my primary mount
  • iOptron GEM28: my original mount, which I keep around as a backup and star tracker
  • Celestron Nexstar: with the Esprit 120ED, I probably won’t use the 8SE as much for imaging, so I can have a dedicated visual/planetary imaging setup

Imaging
  • ZWO ASI533MC Pro: my primary camera
  • ZWO ASI585MC: my planetary camera (although capable of DSO in a pinch)
  • ZWO ASI120MM MINI: my guide camera attached to the William Optics Uniguide scope for the GT71
  • ZWO ASI290MM MINI: my guide camera for my OAG
    • I originally used this with my 8SE and guiding was difficult. I know most end up using the ASI174, but I couldn’t justify the expense, at the time

  • ZWO 5 position 2” EFW
    • I’ve used this on the GT71, but the added weight added a slight sag/tilt, so I think this is pushing the focuser on the GT71.
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Ryan Faulkner avatar
Ryan Faulkner avatar
Part 2 - Preparation and First Impressions

Upgrades to current equipment
In preparation for the larger, heavier scope I made some minor changes to my existing mount and imaging train:
  • Tilt plate for OAG/camera connection
    • Cannot adjust tilt once connected!

  • Added pier rods to the Nyx-101
  • Swapped tripod’s rubber feet for spikes
  • PrimaLuce dovetail for handle
    • I can’t believe a handle is not included with a telescope this big!

 
Esprit 120ED First Impressions
  • Focus lock design is great
  • Built in rotators, but no position markings
  • Prefer the WO built-in handle
  • WO focuser is smoother, but 120ED is SOLID
  • 77mm for focus, which is near the limit
    • I was worried that I would hit the limit of the focuser and not achieve focus
    • For my GT71, focus is achieved at a comfortable 30 mm

  • OAG was easy to focus
  • 0.5” guiding!
  • Did not miss the WO built-in Bahtinov mask
    • While having the mask included with the lens cap so you don’t forget to pack it, using an external mask is the same

  • It's so much bigger than the GT71 (see second image)


Ryan Faulkner avatar
Ryan Faulkner avatar
Part 3 - First Light!

I have only been able to capture 90 minutes of data for NGC 2359 - Thor’s Helmet, but the results look promising!
Attached is a basic Siril stack and autostretch with no processing.
This is from a Bottle 5 sky using the Optolong L-Ultimate filter paired with the ZWO ASI533MC Pro. I am so happy that I don't have to fight back focus.


Guiding was also good enough for me:
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Luka Poropat avatar
Luka Poropat avatar
I see no weight bag in use, tripod feet spiked meant to be embedded into soft ground but instead being used on concrete, a pier extension that "looks" like its not nearly rated high enough for that setup on a tripod recommended for 15kg payload, all holding up a $3500 refractor.
Noice.


"If it works, it works."
Ryan Faulkner avatar
Ryan Faulkner avatar
Luka Poropat:
I see no weight bag in use, tripod feet spiked meant to be embedded into soft ground but instead being used on concrete, a pier extension that "looks" like its not nearly rated high enough for that setup on a tripod recommended for 15kg payload, all holding up a $3500 refractor.
Noice.


"If it works, it works."

Total weight is 12.25 kg (OTA, rings, filter wheel, cameras & raspberry pi).

The default pier from Pegasus is 3 rods, so I’ve doubled that and it is very stable.

I found that the rubber pads introduced a lot of vibration, which others have also encountered on different tripods:
https://stargazerslounge.com/topic/414497-spikes-or-rubber-feet/#:~:text=I%20prefer%20spikes.,that%20makes%20it%20super%20solid

Thank you for your concern.
Alan Brunelle avatar
Alan Brunelle avatar
Not to sound fearful, but I always am when it comes to expensive precious gear.  But the photos, to me, look as if this setup could be unstable and fall over.  I will assume that you have tested all possible scope positions and even those that can occur during a meridian flip.  And at the higher speeds of a meridian flip.  While these mounts claim very good load support without a counterweight, these loads are dependant not only on how much weight they can handle, but also where that weight is.  To add to that, while the mount head can handle the weight, the stability of the whole thing depends on the footprint of the tripod.  And that tripod looks small for the scope.  Support is best when in line of the the legs.  However, the linear distance of the mount head center to a line between the feet is quite small and that is how the tripod will tip, given the chance.  So be sure to check that all out.  

I can see how rubber pads could allow a bit of sagging as the weight of the telescope moves.  However, the translation of vibrations on the ground, such as walking or cars driving past will be transmitted to the rig much more efficiently with hard contact (i.e. spikes) rather than with rubber.  I think the lesson is that you should try to minimise being active around the rig during imaging.  And then it won't matter what you have on the feet.
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Monty Chandler avatar
Monty Chandler avatar
You'll love the 120ED. at 860mm it is wide enough to capture dark nebula and the big galaxies!  I love mine!
Ryan Faulkner avatar
Ryan Faulkner avatar
Update: I think there is something wrong with the focuser. The fine focus knob will stop at 55mm, 65mm, 75mm. If I nudge it past that point with the coarse focus, it will continue to work. I'm trying to use the adjustment screws, but I have no idea which ones to use. Sky-Watcher support says:
"Each corner has its own set of
screws. The inner screw is a stand-off,
while the outer screw is the tension.
You will need to balance those until
the focus runs smoothly."


I guess that means the screws aligned diagonally? It doesn't really matter, because they're all filled with blue lock-tite!


We'll see what Sky-Watcher support has to say. I'm beginning to regret not buy the WO 120FLT instead
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Monty Chandler avatar
Monty Chandler avatar
Why would you touch those screws?  The focuser lock is that compression bar. I put a sesto senso 2 auto focuser on.  Focus at about 80mm, almost fully extended.   Very stable focuser.
Ryan Faulkner avatar
Ryan Faulkner avatar
Sky-Watcher support says to use those for adjustment! 
I think the focuser was bent when it was packed: the coarse knob without the fine focuser has an obvious wobble to it.
I’m very disappointed with the quality and I’m fighting with my local shop to exchange this.
Monty Chandler avatar
Monty Chandler avatar
The good news is that once you are in focus the focuser only moves a millimeter or two from then on.   My 120ed focuser has been at 80ish mm (almost fully extended) for the past two years. Autofocus 8 times a night in the winter.
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