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Help me choose my next Astrograph please?

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#1 mayhem13

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Posted 05 August 2021 - 11:03 PM

Hey folks……so the proud owner of a brand new Celestron CGX this week and looking for a big gun to use with it. Currently working with an AT72ed2 and a Celestron C5 with and without reducer. Still using the 12” Dob for planetary but it’s time for some galaxies and nebula……Orion this winter for sure.

 

10” imaging Newt?…..8” SCT?…..Edge HD?…..5” refractor?…..maybe AT125edl?……

 

thx……my gut says 8” Edge Hd and .7 reducer…..can do visual as well where the Newt poses some challenges with comfortable viewing. The 5” refractor is equally attractive but not exactly a deep sky beast at 975mm. Maybe just a C8…..no edge…..save some $$$ for another scope? Lol



#2 chanrobi

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Posted 05 August 2021 - 11:21 PM

Dual RASA 8 my friend



#3 Jim Waters

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Posted 05 August 2021 - 11:53 PM

RASA 11 V2



#4 DJL

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Posted 06 August 2021 - 01:45 AM

Having experienced a C6, I have learned that even with its own brand flattener / reducer, the stars at the edges are never going to be sharp. So I'd personally choose Edge HD over the C8. 



#5 mayhem13

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Posted 06 August 2021 - 07:03 AM

Dual RASA 8 my friend

Couldn’t I do Edge 8 and Hyperstar later if i decided?



#6 ChrisWhite

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Posted 06 August 2021 - 08:58 PM

"Deep sky beast"

 

975mm FL is indeed a deep sky beast if you are using the right camera on it.  Tiny pixels like the latest BSI Sony chips have, or even the 183, etc... will give you sampling that gets you below the seeing limit.  If you are using a tiny pixel camera, you wont necessarily resolve more details with a longer focal length scope.

 

Also something to consider is that the Edge 8 reducer does not perform all that well.  To my eyes color management is pretty poor off axis and results in some funky looking stars. 

 

What are your goals?  The scopes you list are all very different from one another.  Having imaged with small refractors and newtonians and now a 5" refractor and an Edge 925 they all have pros and cons depending on what your goals are.



#7 mayhem13

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Posted 07 August 2021 - 06:01 AM

Thanks Chris…..still using a Canon APS DSLR at 3.7 per pixel….the T8i. Input read noise is surprisingly good thanks to the Digic8 processor. 
 

Goals?…..faint small galaxies and nebulae. I figure now that I have a capable mount, let the aperture and focal length do the fine work with the heavy lifting part resolved. Optical quality is a priority but cost effectiveness is also built in…..just dumped quite a bit on the mount so not looking for a divorce either. I do get a rather fantastic deal on Celestron stuff from my local retailer so whenever possible. Right now, the EDGE 8 ‘seems’ like the right move…..maybe a reducer from a different mfgr? I would assume that a comparably priced 5” refractor won’t have comparable optics……I’m gonna wind up in the 3-4K range?



#8 ChrisWhite

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Posted 07 August 2021 - 08:06 AM

With 3.7um pixels you will be grossly oversampled at 2000mm focal length. A better match for your camera would be an 8in f5 or 10in f4 newt, if the mount can handle it.

Exposure length would be much shorter with a newt which despite your dslr being a good one it won't compare to the low noise of a cooled astrocam.

Collimation with a newt is trickier than an sct. Everything is a compromise though.

With my edge I bin 2x2 with my 3.76um pixels.

I'm considering not keeping the edge as my 5in frac does everything I need, including seeing limited resolution. I'll do some tests next galaxy season to make that decision.

Edited by ChrisWhite, 07 August 2021 - 08:06 AM.

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#9 matt_astro_tx

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Posted 07 August 2021 - 10:38 AM

I've been told that the hyperstar isn't as easy to install and collimate as you'd think.  Recommend you talk with someone that's used it before pulling that trigger.

 

Couldn’t I do Edge 8 and Hyperstar later if i decided?



#10 mayhem13

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Posted 07 August 2021 - 11:37 AM

I've been told that the hyperstar isn't as easy to install and collimate as you'd think.  Recommend you talk with someone that's used it before pulling that trigger.

Got it!......and Chris has me thinking about an 10" fast newt astrograph now......at 1000mm focal length and 32lbs, should be a good fit for the CGX. Yeah.....Hyperstar is a bit of chore on and off.....more trouble than it's worth i think.



#11 ChrisWhite

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Posted 08 August 2021 - 06:36 AM

Everything is a compromise, and I think that's the main thing to keep in mind. A 10in newt is a beast! An 8in sct is a toy. Collimation is more challenging with a newt, and cheap newts are... well... cheaply built.

One of the biggest upgrades I made in my imaging was going from a dslr to a cooled astrocam. This combined with a moderate FL refractor might give you more for your money than just the biggest longest scope you can manage on your mount.
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