View Full Version here: : Guidescope for 8" SCT

15-08-2017, 12:21 PM
I used to have an ST80 mounted on top of my tube as a guidescope. Although it worked ok and the weight is fine I never really got it configured correctly as a guidescope.

For those with an 8" or even bigger SCT what do you use for a guidescope and how do you mount it?


15-08-2017, 02:41 PM
Hi Stefan this is my 9.25 but It can be quickly moved to my C8 or 65Quad if needed. WO 50mm GS and rings on Losmandy clamp on Baader dovetail, it works well coz I can slide to achieve balance, still building this rig up, hope it helps..

15-08-2017, 02:53 PM
And anutha for perspective I have a slide weight on bottom as well and can achieve perfect balance each way which is critical on the Heq5 with this much load...

15-08-2017, 03:17 PM
Hi Brenton.

Nice setup.

How do you find the 50mm with your SCT? I saw some Orion 50mm mini guidescopes but they recommend with telescopes only up to 1500 focal length. Mine is 2032 and I think yours will be around the 2400 mark.

I have one of the below, could that be used?

15-08-2017, 03:36 PM
As I said Im still building this rig but as far as visual goes its fine. For guiding I guess Ill find out when weather and time permits. Ill use it to sort my 9.25 setup and hone my AP skills. Train of thought leans towards OAG, prob better people here than me to answer suitability, I saw somewhere some complaints of odd shape stars guiding with the 50mm Orion on bigger SCTs. Apart from the maths trial and error I guess....

Just found this in my bookmarks hope it helps...


and this


15-08-2017, 03:42 PM
Hello Stefan
Maybe an Off Axis Guider is an option at that focal length?


15-08-2017, 03:48 PM
Yep, I just started to look them up as I have never really known what they were until now!

I also have a focal reducer to 6.3 which I can throw into the mix as well. My guiding camera would be the Flea3 that I have in my sig below and I will use my DSLR for capturing.

15-08-2017, 03:48 PM
I will have a read of that, thank you!

15-08-2017, 03:50 PM
The OAG can be a little fiddly to set up but as long as your guide cam is sensitive enough they work well (well do for me at 1370f/l

15-08-2017, 06:49 PM
SW 102 F5 achro SSAG .. worked really well.
I fabricated a mount for it from flat steel stock

15-08-2017, 07:41 PM
I have an Edge HD8 and have used two guide scopes: the first was a 60mm ZWO guidescope, but have just switched to a Celestron 80mm guidescope which is on sale at Bintel, complete with rings and clamps. The focal length of the Celestron is a better match with the Edge. I have also tried OAG and had a horrible time with it, settled on the Celestron 80.

22-08-2017, 07:14 PM
Obviously Im trying to keep the weight down on my C9.25/Heq5 and with 6.3 FC Im at 1480mm if my math is correct. Im trying to avoid using heavy 80mm GS. I just saw a vid where a guy used a 3x barlow on his 60mm guidescope to bring the focal length from F3.6 I think to F11 which solved his guiding probs, anyone gone down that path or can verify?

22-08-2017, 08:13 PM
Hi Stefan,

I have the Orion ST80 on my 10" SCT and it works really well. I have the full telescope length dovetail thingy, and I bought some decent tube rings for it. It's a very simple setup and all you need to do for aligning, is setup the guiding camera and the main imaging camera and ensure they are both pointing the same direction/rotation. Then find a bright star to centre the main camera on and adjust the ring adjusters on the guide scope so that the guide camera sees the same star then fine adjust to centre it.

When I first setup my guide scope, I used the 50mm finder that is also attached to my scope to help roughly line up the guide scope as there was a wider field of view which made it easier to find the target.

The other thing to note is to have a fairly close F# with main scope and guide scope. Like you, I have the F6.3 focal reducer and I find it works well as the ST80 is F5. Close enough. When all is setup correctly with my rig, guiding works very well with the ST80. I use a QHY5 mono for the guide camera and so far, this has worked well too. :thumbsup:



23-08-2017, 11:32 AM
I used to have the ST80 pack (bag, eyepieces, finderscope, etc) but sold it as it wasn't really getting any use.

I recently purchased the Celestron Guidescope package which looks like a great bit of kit. Only managed to open it up and have a look, seems a bit on the weighty side though.

Also used to have the QHY5LII Mono but sold that too haha.

I just need to hunt down a mounting bar and a mono camera for guiding and should be good to go.

I am a bit conscience about the weight though. The HEQ5 Pro I think has a payload of 12kg - 13kg so based on the calculations below...

- C8-A XLT (CG-5) (5.67kg)
- Guidescope package (3.03kg)
- Guidescope camera (0.2kg???)
- Mounting bar (1kg??)
- 1200D Body (0.5kg)
- DSLR adapter, focal reducer (0.5kg)
- Finderscope (0.68kg) or red dot finder (0.2kg)
- Dew band and shield (0.3kg??)

Total between 11 - 12kg

I think it should be alright.

23-08-2017, 02:31 PM
I started reading this thread, then... everything got huge shiny and uber impressive! Gentlemen, great rigs!


24-08-2017, 11:41 AM
So regards smaller guidescopes and barlows I finally found the video, for those interested or care to comment...
also the comments below vid have interesting info..

24-09-2017, 06:28 PM
Very useful video, this dude is awesome!

24-09-2017, 07:21 PM
I'm currently running a zwo asi034c as a guide camera through a cheapo cannibalised National Geographic tabletop reflector (350mm f/l).....weighs absolutely nothing....maybe 300gr, prob less....it's basically a wafer thin piece of sheet metal with a tiny mirror
Got that sitting on top of a 150mm skywatcher reflector
Who says you need a refractor as a guide scope??? You don't need colour and detail to guide......you just need a point of light.

Works great!

26-09-2017, 09:52 AM
OK based on more research....

I used this calculator here to work out my focal length after using my Celestron f/6.3 (http://www.wilmslowastro.com/software/formulae.htm#FR_b)

My focal length goes from 2032mm down to 1294mm which should be suitable for the ZWO.

26-09-2017, 01:42 PM
Stefan, I'd go for a bigger guide scope than the ZWO...something with more aperture and focal length. The Celestron package that Glen mentioned would be a better fit.

The thing with guiding is that you want to catch subtle movements before the main camera sees it. With the 1200D, the pixels are small and at >1200mm focal length you will readily see any guiding errors. The more light and detail you can throw into the guide scope the better IMO.

26-09-2017, 01:54 PM
Unless you have some kind of mirror lock I'd recommend using an OAG for any SCT or you might find yourself limited in exposure time because of flexure, no matter how tight your guide scope is, your primary will always shift a little. A three point lock to support the primary is ideal. It supports it while still letting the glass expand and contract with temperature without stress. An OAG will follow a mirror flop, so worst case scenario will be a slightly tilted field but no star trailing over time.

26-09-2017, 03:24 PM
Yep that's what I did but that Celestron Guidescope pack is so heavy. It's around the 3 - 3.5kg mark.

26-09-2017, 04:17 PM
Shouldn't be any problem on a HEQ5. The C8 itself is ~6kg. Your total payload shouldn't be much over 10kg by the sounds of it. Balance is most important.