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Questions on mounting my 8-inch Celestron tube on a more modern mount

Astrophotography Celestron Equipment Mount
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#1 stevejbo

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Posted 01 October 2022 - 07:21 PM

Sorry for the large set of questions - but I am trying to upgrade and the issues are all inter-related. 

I have been doing astrophotography for about 3 years now with a really old telescope.

 

I have an old Celestron Celestar 8 that I have over the last few years been using for astrophotography, though keeping it aligned has been a challenge (I can only do 10-15 second exposures and every half hour I need to recenter the view) . I have been using a Canon R5 attached to the Celestron (or to just a zoom lens attached to the R5 for large objects like Andromeda). I have decided to upgrade, though for financial reasons I can’t upgrade everything at once so my plan is to buy a better mount—I am planning on a EQ6-R Pro--and a tracking scope and a mini-PC to run the tracking scope. I have a Mac laptop so I can WiFi into the mini-pc to use the tracking scope. In future years think about a dedicated astro camera and possibly a wider angle telescope but for the next few years I hope to stick with the Canon R5 and the Celestron attached to the EQ6-R. I am hoping to get some questions answered so I don’t make a costly mistake:

1) Will I be able to attach the Celestron to the EQ6-R? I see on the forum that some have attached larger telescopes to this mount - - is there anything I should be aware of?
2) The Celestron has a fork mount which I would unattach. I found what I think is the right type of Losmandy Dovetail that should attach to the Celestron and allow me to attach it to the mount. Does this look right or is there a better way? https://www.astro-physics.com/lmdc8
3) To attach the secondary camera to the aiming scope I imagine I have two choices – attaching it to the top of the scope or using an off-axis glider. I already have an off-axis glider but I have not used it much as I needed to change the focus of the telescope from what was working with the camera to use it. Would the off-axis glider work with a secondary camera – or would it be better to buy a secondary camera AND a small tracking scope? If both would work or the off-axis solution would work better that would save me some $$ - but is it more difficult to use? Note that the telescope is 2032mm  but I use a Celestron reducer f/6.3 which decreases the focal length.
4) If the answer is to use a tracking scope most of the setups I see online have a telescope that has a smaller aperture. I was thinking something like William Optics UniGuide 50mm Guide Scope or a ZWO 30 mm f/4 Mini Guide Scope. The camera I was thinking of is ZWO ASI120MM-S Monochrome CMOS Astrophotography Camera. For the mini-PC a MeLE Quieter 2Q J4125. If I go with the off-axis glider would I need a different camera type?
5) Does the tracking scope aperture need to be closer to the main scope?
6) If the answer is it is better to use a tracking scope is it better to attach an extra dovetail or to attach and use tube rings? Do I need tube rings for anything? What about attaching the small computer to the setup to run the tracking scope and save the data – I have seen others use that in their setup.
7) For the tracking camera I am thinking a ZWO ASI120MM Mini Monochrome CMOS Camera. Thoughts?
8) Am I going to have issues commanding the mini-PC with a Mac laptop? Does the software work well on the Mac?
9) What am I forgetting?

 

Thanks in advance

 



#2 pedxing

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Posted 01 October 2022 - 07:39 PM

An off-axis guider is preferred, especially if you have experience setting it up.

Do use the focal reducer.

The mount can handle a c8.

Imaging at that focal length is challenging but not impossible. You will hear a lot about how it's not recommended but I say go for it and see how it goes.

#3 pedxing

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Posted 01 October 2022 - 07:43 PM

The 120mm isn't a very good off axis guide camera, you will have difficulty finding guide stars. Try binning in PhD, but a better (more sensitive, larger sensor) guide cam is probably in your future.

#4 pedxing

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Posted 01 October 2022 - 07:45 PM

For controlling the mini PC you will use remote desktop software, not sure what works with a Mac...

#5 FRANKVSTAR

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Posted 01 October 2022 - 07:45 PM

  I have an older C8 SCT and it came with a vixen style short dovetail and I had no mount it would fit to so I bought a dovetail for the C8 and there were holes that I could attach the new dovetail with. I feel if you call who ever your getting the dovetail from or email them they will know for sure if the dovetail will work on your scope, although I think it should. I can tell you the EQ6R pro is a very good mount, I have one and it handles the C8 with camera very well. I don't guide as of yet even though I have the equipment. However I can take 60sec to 120sec unguided and I get good results, not perfect but they are good enough for me and to show others. I use the ASIAIR PLUS with a tablet and it does great, I have a triple finder bracket, 1 for the ASIAIR 2 for a laser finder, 3 for a guide scope. They don't ad to much weight.



#6 EdDixon

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Posted 02 October 2022 - 04:08 AM

The EQ6-R Pro is a very good mount.  The older C8 may be a limiting factor.  Moving towards a lower cost refractor might be a good thing to consider. 

 

I have both the ZWO ASI120mm camera and the ZWO 30 mm f/4 Mini Guide Scope which work well together for guiding.  I use a miniPC at the scope for control and work from inside via VNC or remote desktop. VNC works for a Mac as well.

 

The Canon R5 is a fairly high end DSLR.  Most here will use dedicated astro cameras like ZWO or QHY.  Most who do remote control will also use an electronic focuser.  The ZWO EAF is a good one that fits a range of scopes.



#7 stevejbo

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Posted 02 October 2022 - 10:34 PM

Thanks for all the advice

 

If the 120mm would not work with an off-axis guide camera what would be a good choice? 



#8 stevejbo

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Posted 06 October 2022 - 08:53 PM

I think all my questions have been answered other than what tracking scope would work with an off-axis guider? What is important in choosing this camera? 

Thanks in advance



#9 Mike7Mak

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Posted 07 October 2022 - 02:49 PM

I already have an off-axis glider but I have not used it much as I needed to change the focus of the telescope from what was working with the camera to use it. Would the off-axis glider work with a secondary camera – or would it be better to buy a secondary camera AND a small tracking scope? If both would work or the off-axis solution would work better that would save me some $$ - but is it more difficult to use? Note that the telescope is 2032mm  but I use a Celestron reducer f/6.3 which decreases the focal length.

The trick to using an off axis guider is it has to be set up so the imaging chip and the guiding chip are exactly the same distance from the prism in the oag so both cameras come to focus at the same time. And the next hurdle is after the two chips are equidistant from the prism the total length of the imaging train has to fit inside the required backfocus of the reducer. That is not always easy to accomplish if the reducer's required backfocus is short.

 

Getting an oag set up can be daunting the first time you do it but the effort is well worth it especially on a moving mirror SCT. I seriously doubt you'd be happy with the guiding performance of one of those tiny 30/120mm finder shoe guidescopes.



#10 stevejbo

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Posted 08 October 2022 - 02:28 PM

Thanks for the advice. Is that the idea of the ring on the OAG - - to get the distance set so they are the same? I figured that was what it was for. So you probably just need to get that right once - and maybe fiddle with it a bit each time? Or is there a way to move the guide scope in and out to focus?   Also - a suggestion on what guide scope would work well with an OAG would be really helpful

 

Thanks for all the great advice



#11 Mike7Mak

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Posted 08 October 2022 - 03:04 PM

I'm not sure what 'ring' you're referring to. Generally speaking, for initial setup, measure from the center of the prism up to the top of the stalk where the guide cam mounts. Add about 10mm to that and use spacer rings between the oag and main camera to get that distance from the prism to the chip in the main camera. Depending on how the guide cam mounts you will either have to adjust a focusing mechanism or slide the guide cam up and down to find focus. You will do that after making sure the main camera is at focus.

 

The 1.25" format guide cameras are usually much easier to get working on an oag. Any one of them should work but for an 8" SCT I think the ASI174mm mini would be ideal. If the prism is small on your oag then the 174s larger chip might be a waste.



#12 stevejbo

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Posted 08 October 2022 - 04:05 PM

Very helpful - - thank you!  The cost of the guide scope is a bit steeper than I had planned on - but the cost of the add-ons can start to add up

The OAG I have is https://www.worthpoi...ider-1773650693

The ring I was referring to is the ring on the left hand side of the second picture (kind of hard to see). I can rotate it so that the distance to the camera is changed - - I figure I need to adjust this so the distance to my Canon camera is the same as to the guiding camera - correct?  How can I tell if the prism is too small? Eyeballing it it appears to be about 15 mm



#13 Mike7Mak

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Posted 08 October 2022 - 11:19 PM

If there's an adjusting ring at the T2 camera side it's probably for making fine adjustments to main camera spacing. You may or may not also need a T2 spacer ring depending on the main camera backspace. There also appears to be a ring/helical focuser on the guide cam tube. That oag could definitely use one of the mini 1.25" guidecams. That will allow the shortest spacing distances because the guide chip will be down inside the tube. A regular guidecam with a nosepiece will have the chip sitting at the top of the tube. The prism looks large enough for the 174mm camera if you can swing the 400 bucks for it.



#14 stevejbo

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Posted 10 October 2022 - 10:40 PM

The price is a bit steep - - what about the ZWO ASI120MM Mini Monochrome CMOS Camera for $150?  Would that be sub-optimal for a guide scope?

If the 174mm would work much better I can splurge.....



#15 stevejbo

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Posted 23 October 2022 - 07:41 PM

I researched the 174 in old CloudyNights posts and it seems like the discussions say it is worth it. I don't really understand why since dont you only need 10 stars or so? It appears to be related to the pixel size allowing for better tracking

 

My hopefully final question - - I could go with a mini-PC running NINA or go with a ASIAIR - - my understanding is that the ASIAIR probably won't be able to talk with my camera - -  a Canon R5.

Will I have a way to connect the Canon to the PC/NINA?

 

Thanks in advance




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