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10 inch F4 Newtonian or 10 inch F8 RC

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#1 xmj0001

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Posted 24 September 2021 - 10:14 PM

I have a CGX-L (Hypertuned) mount in my backyard, I've been using it with my C8 OTA and EON 110 APO.  The mount is working very well but I'm considering getting a more DSO astroimaging focused OTA.  First thought was getting a C9.25C11 but I'm rethinking that because i heard that SC aren't that good for DSO compared to RCs and Newts.  I have a more portable setup Celestron AVX/Radian Raptor 61/ZWO ASI183 MC Pro/ASI AIR Pro controlled that I'm using for wide field.  This setup will be permanent in my backyard maybe move once a year if that at all so weight is not issue.  In fact I plan to leave it out in the weather year round cover tightly with a telegizmo 365 cover until i can get a dome. So RC or Next give me your suggestions, I plan to remote control this setup with a ASI AIr Plus when it arrives and i will be using a ZWO EAF for auto focusing.

 

Current candidates:

 

Newt : https://www.astronom...-newtonian.html

 

RC : https://www.astronom...tical-tube.html

 

I know i will need to get a coma corrector with the Newt that the RC doesnt need but it costs twice as much and is twice as slow F4 versus F8.  How is the focusing between the two, and will the EAF be difficult to install and use to autofocus?

 

I would expect both setups to be around 45 pound after adding guide scope, ASI AIR Plus,Guide camera, EAF, Imaging Camera, EFW which should easliy be handled by the CGX-L: (75 pound capacity)

 

I will prbably sell the EON110 eventually and acquire a used CGX to use with the C8 which will be way more portable than the CGX-L

 

BTW : here's a link to a image i recently took with the Raptor 61 in the Bortle 6 skies at my house : https://www.astrobin.com/58bilr/

 

Rich H



#2 Echolight

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Posted 24 September 2021 - 11:15 PM

You know what I have recently discovered to use to cover my AVX, so I can leave it out and won’t have to disassemble or carry it. A used blue plastic 55 gallon drum is a bit cheaper than a telegizmo. Or a lot cheaper. And they last for a really really really long time.

It’s a little heavy, or just bulky. Think I’ll put a handle on the side.

 

Probably wouldn’t fit over a big scope though. But a C8...

 

I think I’d like a 190MN.


Edited by Echolight, 24 September 2021 - 11:18 PM.


#3 tloebl

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Posted 27 September 2021 - 09:57 AM

Have to watch the moisture from the ground if the cover is touching the ground all around like a drum.



#4 MitchAlsup

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Posted 27 September 2021 - 11:49 AM

First thought was getting a C9.25C11 but I'm rethinking that because i heard that SC aren't that good for DSO compared to RCs and Newts. 

SCTs are actually pretty good at DSOs (within their aperture reach), 

 

The major advantage of the Newt is speed (F/4)

The major advantage of the RC is zero coma even without corrector.

Corrected SCTs (Edge, ACF) leave little to complain about.

So, I question the presented premise !?!



#5 Dan_I

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Posted 29 September 2021 - 12:22 AM

The answer depends a lot of the camera you own (or you plan to get) but I think that Newtonians are a better match to CMOS-based cameras like those of ZWO.

 

A typical pixel size in these cameras is 3,8 µm (for instance, ASI2600MM) which would give 0.8"/pix in the Newtonian, perfect sampling unless you shoot under exceptionally skies and using a high-end mount.

 

The same sensor would give 0.4"/pix on the RC, so significant oversampling. Of course you could use (software) bin2 but, compared to the Newtonian, the field of view would be divided by half  with the same resolution.

 

This assumes of course that, on your Newtonian, good mechanics and coma corrector allow you to take advantage of the larger field.

 

Regarding the particular model of truss Newtonian that you have in mind, you would have probably to change the focuser at some point, either to a better 2" model for using with a 2" coma corrector or, if you plan to use large sensors, to a bigger 2.5" or 3" model that would accommodate a 2.5" or a 3" corrector (Wynne or Paracorr). I have read on this forum that some users had to reinforce the upper part to avoid mechanical flexure, but I don't have first-hand experience with it.


Edited by Dan_I, 29 September 2021 - 12:26 AM.


#6 Rasfahan

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Posted 29 September 2021 - 03:07 AM

If you have the space for a Newtonian and think your CGX-L will handle it, I would recommend that. The benefit of the RCs are mirror-only optics (No CA as in the EdgeHD reducers), coma-free field (not important for pretty pictures), compactness (although the SCTs can be lighter), no mirror flop/shifting and little need for dew management. You buy this with difficult collimation (it really is another level from SCTs and Newtonians).

I would also check out some other, imaging-centered Newtonians (like ONTC or Lacerta) and ask people who are using them about their experience.

The EdgeHD line seems well corrected, too (without the reducer) and you know already how to deal with mirror flop/shift.

As you are in Bortle 6 you will have a lot of stray light, so you will need shrouds for the truss-style scopes.

#7 Poynting

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Posted 30 September 2021 - 12:08 PM

I recently received a GSO 10" f/4 truss scope. I haven't produced a final image with it yet, but I have a few things I did to upgrade its performance. I may make a separate post in the future detailing the upgrades more, but here they are so you can keep them in mind when considering your options:

 

1.) As stated above the UTA flexes a bit, but the fix I found is super easy especially if you have 3d printer access. The two UTA rings are connected with three small metal tubes on the edges and the focuser plate, with the light shroud floating in between. There are grooves on the two rings where the light shroud fits into, but still is loose within them. The solution is to fill one of the grooves slightly so that the light shroud is compressed between the rings tightly and reinforces the UTA. I 3d printed a very thin ring (in quarter sections) to fit inside the groove, you could use tape or something else to achieve the same thing I imagine. The UTA is now solid and the secondary tilt holds much better now as gravity on the mirror changes.

 

2.) When using the stock focuser with 2" travel, the Paracorr 2 will not come to focus at longest travel unless you pull it out from being flush with the compression ring edge. The solution was to cut and machine some square aluminum channel to extend the UTA out 2" from where the truss tubes meet so that the image plane is brought in 2" inward from where it was. Now the GPU 1x and Paracorr II 1.15x correctors work within the 2" travel. The focuser thusfar appears sufficient, we shall see in the longterm.

 

3.) My conical mirror has gaps in the coating around the edges, likely from clamps that were holding the mirror during coating, Unfortunate as there are no clips to worry about, but still get ugly diffraction on bright stars. I 3D printed some custom mounts to hold up an aluminum annulus above the mirror to mask that outer portion. Stars look great now. The 3d printed mounts are 3M VHB taped to the metal tilt plate the mirror mounts to, below the mirror.

 

If anyone has any further interest in these changes let me know, I can detail and share everything. 


Edited by Poynting, 30 September 2021 - 01:48 PM.


#8 bokemon

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Posted 01 October 2021 - 03:03 AM

To be realistic, both of the linked scopes are going to be out of stock for a long time.



#9 Lagrange

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Posted 03 October 2021 - 08:11 PM

To be realistic, both of the linked scopes are going to be out of stock for a long time.

Don't know about the Newt but the RC is in stock in some European suppliers under different brand names so it might not be that long until Astronomics stock it again.




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