#Mach2GTO C14Edge HD rig - A Couple Questions #Mach2GTO

Greg Vaughn

Hi Deonb,


Thanks for sharing the photos of your rig.  Very impressive.


Wanted to ask just a few questions about your rig:


  1. The mirror locks on your Edge 14 appear to have been converted from the pointed plastic ones to flat knobs.   Can I ask where you found these or whether they came with the C14 Edge?   I have a C11 Edge and those locks are important but often seem to get in the way when changing equipment in the image train.
  2. I just recently assembled a ZWO MM CMOS camera, a filter wheel and an OAG with guide camera.   I used a very similar ZWO camera for the guide camera, but it looks like I oriented it differently than yours.   Mine has the long dimension tangential to the image circle.  It looks like you have it orthogonal.   Is this to make sure that your sensor dips into the image circle?  Curious about your thought process and any common practices in this choice that I may not be aware of.
  3. Is the ‘Saggita’ OPTEC device a focuser for your guide camera?   If so, what are you using for your primary focuser (is that the OPTEC Leo?) and any thoughts or lessons learned about these choices?  No problem fitting everything in within the backfocus spec for the reducer?


Again, thanks for sharing quality photos of your rig and your observatory – looks very efficient and tidy as well.  Clearly oriented for remote and unattended operation!


Clear skies!





Greg Vaughn

Alexandria, VA

Virus-free. www.avast.com


1) Sure. It is part #19792 from Optec.
The mirror lock knobs on the C14 EdgeHD are closer together than on the C11 EdgeHD - go figure... On the 11", the TCF-Leo fits nicely between the mirror lock knobs. On the 14" it doesn't. Note that these aren't technically needed when I have the reducer on, like in the pictures, but without the reducer, the TCF-Leo would bump into the factory mirror locks and won't fit at all. I don't know if these will fit on a C11 EdgeHD. They're great though, I much prefer their feel of them to the factory mirror lock knobs, so they're staying on regardless.

2) I'm unsure what you mean? Are you concerned my OAG pick-up prism dips into the area of my image sensor? It doesn't - the Prism is at either the top or the bottom of the sensor - not sure which, but I made sure it was on one of the two long edges of the main image sensor when I put in the OAG. The camera is a full frame (ASI6200), and I have a 54mm train at the back so it's tight, but the prism definitely doesn't dip into or shadow the image circle. I wish I could do 68mm up to the OAG, but my rotator internally is 54mm. Ether way I don't think a C14 EdgeHD will project out much further than 54mm anyway. PHD2 just see half-stars, but it works fine. Also night and day difference in guidance after switching my guide camera from a 290MM to a 174MM.

3) Yes the Sagitta has an optional focuser. Without the focuser it's still a great, slimline OAG. But I do have the focuser on there. Honestly, the 174MM instead of the 290MM was a more important change than the focuser. The 290MM needed exact focus to guide, the 174MM doesn't. It's nice for initial setup after assembly, but I don't touch it again after. On the 290MM I had to adjust the focus every few days, which is why I got the focuser, but it's no longer needed.

The Sagitta focuser goes into the same focus controller that the TCF-Leo goes into, by using Ethernet cables. The LEO is the overall primary focuser.

Note that I also have a Celestron mirror focuser on there. The reason for that is there is this delicate balance you need to play between mirror position and backfocus distance (affected by the TCF-Leo and mirror position). The Celestron focuser affects mirror position, the TCF-Leo affects backfocus position. Both can achieve focus. However, the Celestron mirror focuser sucks and does not give repeatable results (actually it's the mirror set screw rather than the focuser that's the issue). It's almost useless for doing Filter-based focus offsets. The TCF focuser is pretty much perfect and repeatable, but since it changes the backfocus, it impacts field flatness. So I want the mirror to be in focus when the TCF-Leo is dead center, since I know that's at exactly 146.05mm. But sometimes the mirror will shift so much over time (even if I lock them) that the TCF runs so far out that the edge stars start to elongate. That's where I use the mirror focuser to fix - switch the TCF back to center orientation for good backfocus, then fix up the mirror using the mirror focuser. Before I just did it manually with a Bahtinov mask, but then I have to go out to the observatory to do that.

Note that this whole setup makes the C14 EdgeHD almost comparable in cost with a PlaneWave CDK12.5. If I were to only use the C14 at 2800mm F/7 I would definitely ditch everything and just do the PlaneWave. Or even a PlaneWave CDK14 with IRF90. BUT, the C14 also has HyperStar, and it also has better planetary capabilities in the same form factor without having to change (and store) scopes. Space is of a premium to me until I build a new observatory.

My backfocus comes in nicely at 146.35mm. I actually have to add 16mm of spacers in to fill it out. Here is the full train:

-6.6mm   OPTEC #17803 - Celestron 3" to OPTEC-3600 Dovetail Mount
36.2mm   OPTEC #19740 TCF-Leo at center position
 4.0mm   OPTEC #7847 OPTEC-3000 3-inch to M54 x 0.75mm female thread adapter
 2.75mm  54mm male-male adapter
18.0mm   Pegasus Falcon Rotator
8mm      54mm x 8mm Extension Tube/Spacer
2mm      OPTEC #19951 OPTEC-3000-S short dovetail to M54 x 0.75mm male thread
38mm     OPTEC #19340 Sagitta OAG   (official specification)  --> ZWO ASI174MM 
-4.5mm  Measurement adjustment (The Sagitta is shorter than its official specification).
2mm  OPTEC #19951 OPTEC-3000-S short dovetail to M54 x 0.75mm male thread
8mm      54mm x 8mm Extension Tube/Spacer
20mm     ZWO Filter wheel
-1mm  Filter adjustment
2mm  54mm male-male
5mm  Camera tilt adapter
12.5mm  Camera - ZWO ASI6200
146.35  Total

ote that the original Falcon Rotator and TCF-Leo didn't fit into/over each other like that because the original motor cover was too big. I originally replaced their motor cover with a 3d printed one that I designed:
Pegasus Astro liked my design and so they adopted it themselves, and sent me one of the new covers to say thanks. That's what I have on right now and what makes the Rotator fit over the TCF-Leo. I don't know if they ship the new cover by default with all Falcon Rotators now, but it's certainly available from them if you ask.

Hah on the tidy. It looks like a rats-nest when you stand next to it :)