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8" RC and reducer + Guiding on GEM28

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#1 solaryellow

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Posted 29 January 2022 - 09:04 AM

The plan.

GEM28
Orion 8" RC
(Recommemd a suitable reducer) is GSO re ducer ok?
Aiming for F6.

Guiding..I have an ASIAIR+ love this thing.

Ioptron makes a guiding package, $220or so that plugs into GEM28
But I would.like to use my AA+ and iPad to eliminate extra computers.

Please recommend a similar guiding package that will work with this long FL setup.


Using modded DSLR APS at the moment.
(I miss my Starlight Xpress MX916) but as soon as I find a No amp glow zwo294 equivalent Im.staying DSLR

#2 bobzeq25

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Posted 29 January 2022 - 11:12 AM

On my RC6 I used the RC specific reducer, the CCDT67.  It took my F9 scope down to about F7. 

 

Reducers are designed to work with specific optics.  You're always best off to get what is designed for your scope.  Skimping here is false economy.  Unlike Barlows, they are not infinitely adjustable, they work best at specific F numbers.

 

I had an RC6 on a zeq25.  These scopes are undermounted on these mounts, and I got a CEM60.  You needn't go that far, but it wasn't a waste.

 

Nothing wrong with a DSLR.  The 533 and 2600 (I have both 2600s) have zero amp glow.


Edited by bobzeq25, 29 January 2022 - 11:16 AM.

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#3 solaryellow

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Posted 29 January 2022 - 12:42 PM

On my RC6 I used the RC specific reducer, the CCDT67. It took my F9 scope down to about F7.

Reducers are designed to work with specific optics. You're always best off to get what is designed for your scope. Skimping here is false economy. Unlike Barlows, they are not infinitely adjustable, they work best at specific F numbers.

I had an RC6 on a zeq25. These scopes are undermounted on these mounts, and I got a CEM60. You needn't go that far, but it wasn't a waste.

Nothing wrong with a DSLR. The 533 and 2600 (I have both 2600s) have zero amp glow.


Thank you. I forgot about the 533, originally I was comparing that to the 294, but that was if I was going to continue battling with my ancient 16" Starfinder. Wanted a large field of view
But I guess it wouldnt matter too.much considering at F6 I would essentially get that back with the smaller chip. Plus with a nice new mount, I can enjoy longer Fl imagine.

I could go Orion or Ioptron on the RC. As far as specific Reducer, I didn't know there was one..
Saw the AP and Teleskop, the latter being $500. Wow. GSO was $125.
I wasn't going with the GSO rc because of apparent light leak issues.
GEM28 claims 28lbs

Rc OTA 18lbs
I figure after camera and a few other things I'll be around 22. Probably pushing it, but ill take my chances.

#4 solaryellow

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Posted 30 January 2022 - 07:17 AM

On my RC6 I used the RC specific reducer, the CCDT67. It took my F9 scope down to about F7.

Reducers are designed to work with specific optics. You're always best off to get what is designed for your scope. Skimping here is false economy. Unlike Barlows, they are not infinitely adjustable, they work best at specific F numbers.

I had an RC6 on a zeq25. These scopes are undermounted on these mounts, and I got a CEM60. You needn't go that far, but it wasn't a waste.

Nothing wrong with a DSLR. The 533 and 2600 (I have both 2600s) have zero amp glow.


After looking at the Gem28 I'm.takong your advice and going. A little bigger.

Opinions on CEM40 or Gem45

8" Rc either Orion or Ioptron Maybe GSO if they fixed the light leak issue.
And an autoguider package. Not sure yet.


I think total weight of everything up top will be around 24lbs.

Budget $2800 for mount and guidescope/cam

#5 MrRoberts

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Posted 30 January 2022 - 09:42 AM

You will definitely want the CEM40 vs GEM28. Early on I used my cem25 with the C-8. Barely do' able. The CEM40 is a much better fit for that size ota.

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#6 iwannawon

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Posted 30 January 2022 - 10:17 AM

i might be wrong but i thought all the rc's were just rebranded gso's. so i don't know if that will change the light leak issue. there are posts with 3d printable extensions. i don't have a printer and just uploaded it to a site to print. was something like $4 plus shipping, $8 total. i haven't installed it yet. i'd use other support/cost/availability criteria to decide which to go with. or contact each to see if they did anything specific recently to fix it. my guess is 'no'. the differences are usually paint and accessories. for guiding, look into 'oag' and something like the 290mm mini camera. i use a guidescope with my 6rc but have flexture. i think every post i see with 8rc's suggests oag instead. i already had the guidescope, etc and choose not to repurchase everything but if i was starting over i would go oag. save some 'why aren't my stars round'/'do i have tilt' questions.



#7 solaryellow

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Posted 30 January 2022 - 10:23 AM

Thank you.
That does look like a more solid mount for an OTA of that size. I was also afraid the thing would tip over.

The GEM45 and CEM40 were within my budget.
In reality it was the EQ6R but I'm not sure I want to wait forever to get it.
More decisions I suppose.

#8 bobzeq25

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Posted 30 January 2022 - 11:55 AM

Things to know.

 

Weight is just a rough threshold question for a suitable mount.  It can rule certain setups out.  It can't rule them in.  Because...

 

Focal length counts a whole lot.  Longer focal length magnifies tracking errors.

 

Weight distribution also counts.

 

No one _ever_ regrets getting "too good" a mount.  It's the most important part of the setup.  Keeping dumb .005mm pixels on target is difficult.  With your budget, you definitely need to include a feedback loop to correct mount errors, autoguiding.  It's far from perfect, so the best autoguiding is the least autoguiding.  <smile>

 

Many people get the AP reducer for their Rcs.  It's not because they like spending the money, or want a status symbol.  <smile>

 

The inexpensive RCs have marginal focusers.  Flexure there is one reason OAGs work better for these scopes than guidescopes.  The focuser causes other problems (collimation), many people replace them with Moonlights.

 

The focuser tends to be a bigger problem for most than light leaks.

 

But the real issue with these scopes is difficult collimation.  If you're lucky enough to get a good one out of the box, great.  I wasn't, and it took me weeks to get it right.  Only to discover focuser shift messed up my careful work.

 

Instead of a Moonlight, I got a nice 3.7 rack and pinion focuser.  It came attached to a TS 130mm F7 refractor.  <smile>

 

The two iOptron mounts are comparable performers to the EQ6-R.  The step up these days is a $2700 mount like a CEM70 or Losmandy G8G11.


Edited by bobzeq25, 30 January 2022 - 12:04 PM.


#9 solaryellow

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Posted 30 January 2022 - 01:21 PM

I have some messages in to OPT. It's harder to figure this out with all the availability issues.

The RC light leak stuff I thought was specific to GSO, but yes I have see the little extension baffle tunes. That's not a problem. I'll sort that out when the time comes.
I was going to add the Adjustable tilt ring to my list for the focused. Seems logical.
Collimating I have seen can be tricky.
Any comparison as to difficulty versus collimating a 16" F4.5 newt. Got about 30 years experience on that, but I'm sure I'm looking at a new chapter here.

Lastly. I swore i would never touch an OAG again.
I had a Lumicon Giant Easy guider for my Newtonian, behind a True Tech Flip Mirror and played with a Starlight Xpress MX916 back during the dawn of CCD.
Mind you, I was manually guiding in RA via a quartz RA drive corrector and manually on the Dec tangent arm. Yeah that's how old and out of date I was.. in the OAG I was using an illuminated reticle and for the life of me, I could barely find suitable guide stars. Even with such a big aperture.
It's like it's all new to me again.
If OPT says EQ6R coming soon, then I'll probably get that and use the balance of my $2800 to figure a good guide setup.
If the GEM45 is my other option. That's in stock, then I have figure out if it's worth trying the iguider.. price will be around the same for both options. What's an ideal ratio for guiding focal length to Imaging. (1625mm) or 1200mm
The AP reducer is a good deal. So I can add that.
Thanks again.
This journey has been forever.

#10 bobzeq25

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Posted 30 January 2022 - 07:56 PM

Guidescope works fine for Newts and refractors.  Everything on them is solid, so the main scope follows the guidescope (assuming you have it mounted solidly.  A finder shoe is not solid.)  Plain SCTs and RCs have somewhat flexible main scopes.  So they may not (likely won't) follow a guidescope, however solidly mounted.



#11 solaryellow

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Posted 31 January 2022 - 08:08 AM

Would flexure be less of an issue on the steel tube versus a carbon fiber? One RC I saw had a top rail down the length of the scope, i would assume is better than a simple finder shoe..
I hope OPT calls me back fast.
The Wife is as excited about this as I am. Lol.

#12 bobzeq25

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Posted 31 January 2022 - 09:57 AM

Would flexure be less of an issue on the steel tube versus a carbon fiber? One RC I saw had a top rail down the length of the scope, i would assume is better than a simple finder shoe..
I hope OPT calls me back fast.
The Wife is as excited about this as I am. Lol.

I got the top rail, helped some with the main scope stiffness.   I found the whole scope to be a wet noodle.  <smile>  RC is a demanding design re mechanical quality.  Some people made (make?) good RCs.  They look like space age construction, using carbon fiber/titanium, carefully engineered to handle the stresses.    A 10 inch is about $5000.

 

The real problem is the stock focuser.  And focuser shifting causes errors that are best solved with an OAG.  You won't get full value from the excellent optics without an aftermarket focuser, I believe.  They're quite popular among serious RC imagers, for good reason.

 

As I recall one of the good RCs focused the secondary mirror.

 

These issues (collimation, need for an OAG) are completely dependent on how demanding you are.  But an RC is not some kind of magic cheap big long focus scope.  The inexpensive ones often have mechanical issues.  You may not even notice them.


Edited by bobzeq25, 31 January 2022 - 10:05 AM.


#13 solaryellow

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Posted 31 January 2022 - 07:32 PM

Thanks, I guess I'm in for a new learning experience.
I went with the GEM45
And AP focal teducer. Supposedly for it works best at .72
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