11 replies to this topic

[lostbit]

Hello and good Night.

SO I am again trying and trying to get my CGX with 8Edge working well. 

But I want to use my OAG I am aware at times I might not be able to get a good guide star. 

But I would at least like to get it to work. I the issue is prity consistent, I focus the OAG and I get say three stars.

I tell PHD2 to slew to the calibration location it suggested. But it never calibrates it will ether say the DEC is not

moving or other errors. I look at the log and the DEC line is a blob or scattered dots . I have seen many folks who use the 

Celestron OAG but its costly and I already have at small OAG. I guess I am asking if you have an 8 " sct or edge

do you use an OAG, or do you have a CGX and use an OAG. How well does you setup work.

What is a better guide camera something perhaps with back illumination!

Note I can get good calibration with a 60mm guide scope and the same zwo290mm mini camera. But

then autoguiding is not so good past 60 seconds.

 

Celestron CGX with 8" edge HD using .7 reducer Askar OAG Zwo 290mm guide camera.

[BrentKnight]

Are you mostly interested in doing AP?  I ask because this is the EAA forum where folks might not even do guiding and if they do, their exposures are often less than 60 seconds.  If you are less interested in live-stacking and live-viewing, I can move your topic over to Beginning Deep-Sky Imaging.

[Clouzot]

 I guess I am asking if you have an 8 " sct or edge do you use an OAG, or do you have a CGX and use an OAG. How well does you setup work.

I have neither, but close enough (C9.25 running around f/6.5, so around 1500mm f/l, with which I tested both the ZWO OAG and OAG-L). I also use two guide cameras: ASI174MM and ASI290MM, both mini of course.

 

The 290MM is too small a sensor to consistently get a decent guide star with such a focal length, so I'm using it for parallel guiding, just like what you do with the 60mm guidescope. The 174MM gives much better results, mainly due to its sheer size, but while it's not BSI (Pregius first gen), I don't know of another recent model that would be similarly sized. Your last option is the 220-based cameras (ASI220MM etc) which would probably be a nice fit to your Askar OAG as well, but the field is maybe still a bit small.

 

That said, the fact that you can't guide correctly past 60s is probably a sign of something else at play here. It might be mirror flop (but you have an EdgeHD with mirror brakes). It might be differential flexure, in which case you should use a serious setup for the guidescope (like, two rings, ADM-style mounting on a second dovetail, etc, the usual thing). Or it might be the mount.

[DirtyRod]

I ran an Edge8 on a CGX-L for several years until I switched to a CQ350 mount. The. OAG using a 290 worked OK but the 174 works better and, if you search, you will see that many use this combo. Works just as well on the new mount. I originally tried a 60mm guide scope but I had serious image shift from flexure as mentioned above. With the 290 I was getting 5-7 guide stars but the 174 usually has 10-12 and can hold on to them better during light clouds.

 

Getting an OAG configured correctly takes a bit of work. I assume you focused the ma8n camera first and then make sure you get the guide scope focused before you try to calibrate. Doesn’t have to be perfect but you can just loop the camera until you get the get a good guide star profile. Also important that you get the prism down as far as possible especially if you are running a reducer which blocks about 40% of the FOV on the guide camera. The further down you bring it, the more guide stars are available.

 

After that, if you are not getting DEC movement when you calibrate then, I agree, you may have mechanical issues. The CGX doesn’t not generally have a lot of backlash but it’s possible yours needs to be adjusted if it’s not new. Definitely first want to get the OAG adjusted and focused properly though so it’s not trying to guide on a hot pixel or blurry plane.

Edited by DirtyRod, 24 April 2025 - 08:34 PM.

[lostbit]

Thank you all for your  input, I am now thinking I need to try adjust the dec gear mesh while guiding

to see if I can see any improvement in guiding. I will also  (just for test) use the mirror lock, 

I leave them loose so auto focus runs wont cause issue. Another thought is to try st4 guiding

to remove any issue with CPWI, although guide calibration works fine when I use guide camera and a guide scope.

If I do get a better guide camera I should also go for the Celestron OAG it has a larger mirror and better rotation adjustment.

[Rydeen 98]

The 174mm mini with the Celestron OAG has never let me down.  I don't know what type of OAG you have but you mentioned it's not the Celestron OAG.  The Celestron OAG and the ZWO OAG-L are the only two I'd recommend.  They have large pick off prisms.  Combine that with the large sensor from the 174mm and you should have plenty of stars for guiding.  Before I had this guide set up I used the 120mm with a guidescope and though it had plenty of stars and good guiding numbers, it resulted in serious differential flexure and bad star shapes even with using the mirror locks on my EdgeHD.  It's 100% worth the investment in the Celestron OAG and 174mm mini if you want to image with an SCT.

 

Robert

Edited by Rydeen 98, 05 May 2025 - 01:01 PM.

[lostbit]

well finaly had some time and some clear sky's.

So I did get the Celestron OAG that did not help.

So I changed the OTA to my redcat71 with ZWO 2600 duo

and no problem at all I have easy calibration and very good guiding.

for an hour or so then came the wind.. 

Next night just put the red  cat 71 on and ran more test all good, (no OAG) just

the build in guid chip.

So put scope to home and switched to the celestron 8" HD with OAG and added a\

weight and balanced. 

well failed to calibrate or guide, switched to st4 cable and calibrated ok but guiding 

was total 3.34

also with the 8" scope I use the .7 flattener nina complains mismatch focal length is 1492

I have been told or red in the specs is should be 1422 with flattener. 

so I will change this in PHD2 and Nina tonight and see if that changes anything.

I do have another guide scope I can use in place of the main camera to try that too.

[DirtyRod]

I have been told or red in the specs is should be 1422 with flattener. 

so I will change this in PHD2 and Nina tonight and see if that changes anything.

I do have another guide scope I can use in place of the main camera to try that too.

Nina had me change my EdgeHD8 to 1493 with the reducer and 2143 without to platesolve with ASTAP correctly. I just changed it and it hasn’t complained since. 

[kaymann]

Check this out he is absolutely the best in solving nearly all problems SCT (he owns a C9.25). He, James Lamb, tried his hardest to dump the OAG for a guide scope and the results were not good enough for him (you could definitely see the difference). His channel definitely delves into so many problems we see listed here...

 

https://www.youtube....h?v=0Q5RVZXhAtY

Edited by kaymann, 12 May 2025 - 10:01 AM.

[thierry martin]

Nina had me change my EdgeHD8 to 1493 with the reducer and 2143 without to platesolve with ASTAP correctly. I just changed it and it hasn’t complained since. 

The Edge C8 is around  2,130mm FL  or F10.48   Celestron  withe paper ƒ/10.456  . The reducer  for this specific Edge is 0.7 from f/10.456. 

[River Hills]

I have only recently acquired an EQ6R mount to use with a standard C8. I have a QHY OAG paired with a QHY 462 colour planetary camera. I have only been guiding recently. I found that with my HEQ5 with a 200mm guidescope I got good numbers but elongated stars due to flexure but my rig was too heavy when I put on my filter wheel and cooled QHY 533 (heavy camera!).

 

This prompted getting the EQ6R going with the OAG at a f = 2081 mm. I had miserable results at first with trying to find a guide star but made a breakthrough when I increased the gain and binned the camera. Finding a guide star was not too difficult then. I don't know if the camera gain is automatically adjusted by PHD2 or not. If using Metaguide the bin, gain and exposure need to be set in your imaging software while using a WDM broadcast driver. 

 

At any rate on an evening of decent seeing I was guiding at  RMS = 0.5". As the evening wore on the seeing got worse and my guiding suffered and ended up at 0.7".  I think I could improve on this by dialing in a bit better on the telescope balance and maybe some settings tweaks, but certainly increasing the gain and binning made a big difference.

Good luck.

Rick

PS kaymann has made a very good suggestion about checking out James Lamb's videos.

Edited by River Hills, 12 May 2025 - 05:30 PM.

[jml79]

The 290 has small 2.9um pixels. Try binning to get a more reasonable pixel scale. It also improves sensitivity which may help. Also up the gain as much as you can and still get a good image. If all else fails, point towards the milky way to make sure you have a dense star field. It is much easier to diagnose issues like focus and sensitivity(gain) if you know there are stars in the FOV.