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ZWO OAG w/helical focuser vs. Celestron OAG

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#1 tectonik


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Posted 22 October 2021 - 01:01 PM

Trying to determine which is best for my system:

Celestron C8 with Celestron 6.3FR


Filter Drawer 19.0mm
ZWO spacer 14.0mm
T1 adapter 57.0mm
ZWO 294MC back focus 6.5mm
Total (from back of FR) 96.5


Guide Camera:  ZWO 120MM mini


Will need to change spacing with either OAG I would think.  This is my first OAG.


Thinking the bigger Celestron prism is better (12 vs 8mm, provided no light cone penetration) for finding guide stars and PDH2 multi star guiding.


A very knowledgeable club member recommended the smaller ZWO vs the larger ZWO (OAG-L) due to my sensor's size, however I did not ask for the Celestron comparison.  Would like to get some CN's members opinions as well.


Thanks folks.



Celestron 6.3FR
ASI120MM mini

Celestron OAG








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#2 Linwood



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Posted 22 October 2021 - 01:29 PM

I have the OAG-L, and use with a ASI174MM which is a larger sensor than yours.  I think the plumbing is a bit differet in how it connects so no comment on if you have the exact right pieces.  I've been very pleased with the OAG-L, the helical focuser is much smoother than the Celestron (which I also have). 


I don't know what's in the filter drawer, but one difference in the Celestron and ZWO is that the Celestron has a rotator built in due to the dovetail connection.  The ZWO is screw threads, so the rotation is set by where it gets tight.  You may consider adding a rotator.   I used this one, which is M54, but they have different sizes: 




I was pleasantly surprised at how secure it is, it locks easily, and turns without sag. 


One thing to consider is whether you may ever change to a wider format camera.  Not sure how relevant it is on a C8 (especially non-edge), but the plumbing with a T connector (I assume that's a 42mm) is pretty small.  I'm also unsure whether this is going to add constraint to the room for the prism; it has to extend down into the imaging circle, but stay out of the view of the main sensor along the long edge of the sensor.  Someone who has done a 42mm setup may want to comment if there's plenty of room for the prism, I am not sure.


Personally if I were starting up, I might look at doing an M48 or M54 size path from the back of the OTA, just to provide lots of room, and possibly eventually a larger sensor (if the C8 can support it which I do not know).  The cost for going M48 or M54 is not much more for the plumbing parts, it's the camera that costs more to go large (and to some extent the filters). 


But to your core question: I like the ZWO OAG-L much better than the Celestron OAG.   One key reason is so far I have not seen any reflection artifacts on it, as have been reported on the COAG: 




ZWO's main drawback is the need for a separate rotator, though the backfocus depth difference leaves plenty of room.

Edited by Linwood, 22 October 2021 - 01:29 PM.

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