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Guidescope overkill?

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#1 amdizack

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Posted 06 December 2012 - 01:15 AM

Regardless of guide camera, is using an 80mm refractor (600mm focal length) as a guidescope overkill for an 8" SCT with 2032mm focal length?
Debating on the celestron guidescope package for an C8-HD...

Thanks!

#2 CosmoSat

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Posted 06 December 2012 - 02:39 AM

Wont it cause any balance issues? the f/7.5 focal ratio and the 600mm focal length seems a bit longish for a finder scope...how much true field does it give? 50mm is more than enough really..

Clear Skies!

#3 Raginar

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Posted 06 December 2012 - 03:57 AM

I guess I don't know what you mean by overkill? Yes, you can guide 2032mm with 600mm just fine. I think the larger issue is whether the the Celestron guider is any good. You won't find many good reviews on here.

Good luck!

#4 TxStars

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Posted 06 December 2012 - 04:02 AM

An 80mm refractor will make finding a guidestar easier.
The big problem will be flexure and mirror movement.
At 2032mm fl guiding is best done "On-Axis" or "Off-axis" not with a guide scope though you may get lucky. ;)

#5 CosmoSat

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Posted 06 December 2012 - 04:19 AM

wooppsss.....my bad...I had a finderscope in mind.. :foreheadslap:

#6 snowcrow

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Posted 06 December 2012 - 08:40 AM

I bought the Celestron guide package, and was NOT real happy with it! I have a CPC 1100HD and it was like strapping a boat anchor on top of the scope! I can't balance it out to save my life. The Nexguide is a pain in the @&& to focus and isn't that sensitive. The Nexguide also doesn't allow you to run remotely, so if you plan to in the future, Nexguide isn't for you!!

Orion's 50mm finderscope guiding package is your best bet!!

http://www.telescope...rion-Magnifi...

#7 amdizack

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Posted 06 December 2012 - 10:13 AM

Bill,
I have seen this one, but right from the product description, it says this: "...designed for precise astrophotographic guiding with instruments up to 1500mm focal length".

The focal length of the C8 is over 2000. Seems like even Orion is saying there could be a compatibility issue?

#8 amdizack

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Posted 06 December 2012 - 10:14 AM

ONAG is something I am still learning about. Could you point me into the direction of a good system to start with?

#9 snowcrow

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Posted 06 December 2012 - 02:15 PM

Bill,
I have seen this one, but right from the product description, it says this: "...designed for precise astrophotographic guiding with instruments up to 1500mm focal length".

The focal length of the C8 is over 2000. Seems like even Orion is saying there could be a compatibility issue?


I've heard of them being used on 14" scopes with no tracking issues at all.

#10 Steve Drapak

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Posted 06 December 2012 - 03:33 PM

I'm using a KWikGuider on my 12" Meade SCT with no issues.

You do really have to be very careful with flexure though. I have the guider clamped to the front underside of my losmandy plate upside down. The spur mount that comes with a guider is rarely flex free, and even the threaded front of the guider that holds the lens can wobble. You absolutely have to lock the mirror in your SCT if you want to keep your sanity (I use a Moonlite focuser so almost never unlock the mirror).

ONAG is expensive, Innovations Foresight are the only game in town right now and close to $1000. But if you want the gold standard, it's probably the way to go.

All other ways have issues that you have to work around, either flex with a finder scope system or difficulty finding guide stars and a dim field with an OAG. Unless you spend a lot on the guide camera, you may run into sensitivity issues there too, especially with OAG. LodeStar is supposed to be the best, though it runs around $600. A QHY5 is a cheaper guider, though much less sensitive. Some people cool them with TECs, I might give that a try to see how it affects the image.

Steve

#11 amdizack

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Posted 06 December 2012 - 04:52 PM

If I didn't want to go the ONAG route, would the Orion mentioned earlier be my best bet with the C8HD? Or is there another I should look at?

#12 snowcrow

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Posted 06 December 2012 - 05:04 PM

IMO, yes!

#13 Footbag

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Posted 06 December 2012 - 08:29 PM

I have an Edge 8" and use a 66mm WO guidescope piggybacked. This pushes the limit of the guiding software. An 80 mm may be better, but ultimately an OAG is your best bet for tighter stars. The OAG will require a good guide camera like the lodestar or sbig st-i. For an OAG, the TS9 is what I'm strongly considering.

The benefit of the OAG over the piggyback is that it eliminates any differential flexure, mirror flop or anything else that typically causes frustration. That is not to say they dont have their own frustrations.

The biggest frustrations with OAG's are not being able to get the guide camera and imaging camera parafocal and not being able to find a guide star.

#14 mikey cee

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Posted 06 December 2012 - 08:44 PM

There aren't any hard and fast rules on this. With you if it looks good, balances good and views good....for you then knock yourself out! It's good! You don't need anybody else to tell you what you need. ;) Mike

#15 Steve Drapak

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Posted 06 December 2012 - 09:24 PM

I have an Orion OAG, it works, though with my less than sensitive QHY5 it's tough to find many guide stars.

#16 *skyguy*

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Posted 06 December 2012 - 10:24 PM

Yeah ... overkill! I use an 80mm. f/4 (320mm) refractor for a guidescope on my 12" SCT f/6.3 (1920mm) ... no problems with autoguiding at all!

#17 Ron (Lubbock)

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Posted 07 December 2012 - 01:17 PM

On my 8" SCT, I was using my 60 mm Stellarvue finder as a guidescope, but I could only get 5 minute subs without flexure or mirror flop issues. I sometimes had to move the guidescope off the target to find a guide star in my Orion SSAG, which I hated. I switched to an ONAG last month, and it's fixed all of my problems. There are so many more guide stars available, and 15 min. subs look like my old 5 min. subs. Takes 1 minute or less to find a guide star most of the time.

#18 rigel123

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Posted 07 December 2012 - 01:43 PM

Nope, not a problem. This is my ED80T I use piggybacked on my AT6RC.

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#19 herrindude

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Posted 07 December 2012 - 09:14 PM

I use the celestron guidescope with an orion sharshoot mono imager as an autoguider on my c11 and cge mount and it works great. The only problem i have is the cheap focuser that came with it, my plans are to upgrade it later.

#20 amdizack

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Posted 08 December 2012 - 12:03 AM

So what I'm hearing is the guide scope is a win, but the Celestron autoguider is a fail.

Thanks all!






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