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Guide cam/scope setup

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#1 Deesk06

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Posted 07 April 2020 - 02:22 PM

Hi,

 

I recently purchased a new scope. I ended up going with an 80mm f/6 480mm scope. trying to figure out auto guiding now. So far the plan is to get as follows:

 

ZWO ASI120MM Mini

&

Meade 6000 50mm  Guide Scope. I will link both down below

 

1. Is this a good setup to have?

2. What the heck is flexure when guiding? How is it best fixed? 

3. Thanks for the help!

 

https://www.meade.co...uide-scope.html

https://astronomy-im...120mm-mini-mono



#2 einarin

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Posted 07 April 2020 - 02:31 PM

1. Yes

2. Usually people say that guide scope mount is not good enough for AP and you need more rigid setup.

Here's one thread on the subject:
https://www.cloudyni...or-solid-clamp/

 

(however I have done with such primitive setup with a refractor like yours and even longer fl scope - never had flexure problems but I may be just an exeption)


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#3 Deesk06

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Posted 07 April 2020 - 02:41 PM

1. Yes

2. Usually people say that guide scope mount is not good enough for AP and you need more rigid setup.

Here's one thread on the subject:
https://www.cloudyni...or-solid-clamp/

 

(however I have done with such primitive setup with a refractor like yours and even longer fl scope - never had flexure problems but I may be just an exeption)

Thanks for linking that. I am wondering if it is possible to remove that mount and connect those rings to a bigger dovetail and mount it to the top of my scopes mounting rings. The scope I got has holes to mount on top of.



#4 drd715

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Posted 07 April 2020 - 03:04 PM

That guide scope you link has what I would call a "Stalk" type mount. Ok for shorter imaging scopes, but a more ridged connection would be better. A longer distance between the two rings attached to a longer bar bolted to the top of the main scope rings.

I would be more concerned with "droop" as in the focuser rigidity on the main scope. The draw tube flex/ droop is usually the culprit especially if you are hanging a heavy camera on the end of it. Larger diameter draw tubes and or better quality focusers are your friend. It does help with rigidity if the flattener is threaded on instead of clamped.

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#5 drd715

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Posted 07 April 2020 - 03:08 PM

Thanks for linking that. I am wondering if it is possible to remove that mount and connect those rings to a bigger dovetail and mount it to the top of my scopes mounting rings. The scope I got has holes to mount on top of.

Look at the ADM products. MDS series bar, removable clamps and rings. You can leave the bar on top of the rings and unclamp the rings/guide scope for easy removal.

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#6 Deesk06

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Posted 07 April 2020 - 03:35 PM

Look at the ADM products. MDS series bar, removable clamps and rings. You can leave the bar on top of the rings and unclamp the rings/guide scope for easy removal.

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Okay, so you are saying that guide Scope is sufficient enough then? I will look into those rings and mounts right now

#7 richorn

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Posted 07 April 2020 - 07:23 PM

Okay, so you are saying that guide Scope is sufficient enough then? I will look into those rings and mounts right now

You could also go a bit longer on the guide scope, and kill two birds with one stone:

 

https://optcorp.com/...I8aAmxOEALw_wcB



#8 Stelios

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Posted 07 April 2020 - 07:33 PM

Okay, so you are saying that guide Scope is sufficient enough then? I will look into those rings and mounts right now

You can get a much cheaper 50mm scope from Orion for $79.95. That way you have some cash saved for a better mount (ADM is *the* site for this).

 

The "quality" of the 50mm makes ZERO difference on ability to guide. 

 

Differential flexure results from single-point mounting of guidescope. At long focal lengths (~850mm or more), it can be present even with "perfect" mounting, which is why people use OAG's.



#9 Deesk06

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Posted 07 April 2020 - 08:58 PM

You can get a much cheaper 50mm scope from Orion for $79.95. That way you have some cash saved for a better mount (ADM is *the* site for this).

The "quality" of the 50mm makes ZERO difference on ability to guide.

Differential flexure results from single-point mounting of guidescope. At long focal lengths (~850mm or more), it can be present even with "perfect" mounting, which is why people use OAG's.


Thanks Stelios,

What is your take on getting the ZWO 60mm scope? Little bit better build quality? If it's not much of a difference from the 50mm Orion then maybe I will just go with the Orion. But if I benefit from the 60mm then I have no problem spending the extra cash.

#10 Deesk06

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Posted 07 April 2020 - 08:59 PM

You could also go a bit longer on the guide scope, and kill two birds with one stone:

https://optcorp.com/...I8aAmxOEALw_wcB


Thanks,

I am actually looking into the 60mm ZWO guide scope. Maybe the 60mm will be more beneficial.

#11 richorn

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Posted 07 April 2020 - 09:23 PM

Thanks,

I am actually looking into the 60mm ZWO guide scope. Maybe the 60mm will be more beneficial.

I had the Orion 50mm on a pedestal similar to what you were looking at.  When I got the Zwo 60mm and put it in properly mounted rings most of my guiding issues were solved.  Of course I have no idea which half of the equation was solved by which.


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#12 drd715

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Posted 07 April 2020 - 10:48 PM

Okay, so you are saying that guide Scope is sufficient enough then? I will look into those rings and mounts right now

I'm using a 90mm x 700mm for a guide scope just because I have it. The old theory of guide scope Fl mm was half of the main imaging scope. Some say 1/3 of imaging scope fl. I'm not a fan of the short guide scope except for short systems say below 300mm main imaging scope. A short guider should be good for a camera/lens guider tracker or some of the 70/80mm short scopes.

You can take any simple achro cheapie beginner scope and make it your guide scope. The biggest difference between a purpose built guide scope and a telescope used for a guider is the tube length and focuser type. On a dedicated guide scope the tube is longer before the focuser as it is intended to be used with out a diagonal. A telescope used as a guider might need an extension spacer between focuser and camera. Some dedicated guide scopes use a helical focuser for the camera. What you really need to watch out for is a sloppy wiggly focuser/ extender. It is most important to have a very stiff guide scope with no sag or shift in the camera holder/ focuser mechanism.

Any shift in the system be it in the guide scope and its mechanism or the mounting of the guide scope to the imaging scope and the imaging main scope itself including the main scope focuser/ flattener/ camera attachment will degrade your tracking. Everything has to be solid and rigid or you will be chasing demons.

On 1000mm plus imaging scopes some astrophotographers like the Off Axis Guider - OAG system, but they present some limitations too and are a whole separate subject. OAG guiding is particularly useful with a mirror type telescope that may present mirror shifting while imaging. In this case any optical train movement (minor within reason) will also be seen by the guide camera and corrected out in real time.

Im using the 700mm guide scope on a 1200 mm and a 980mm imaging scopes and keeping everything stiff it works well.

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#13 einarin

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Posted 08 April 2020 - 01:25 AM

I'm using 50mm guide scope with about 200mm fl and guided successfully with 1300mm imaging scope.

Sub pixel guiding really works.



#14 Glass Eye

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Posted 08 April 2020 - 08:26 AM

Thanks,

I am actually looking into the 60mm ZWO guide scope. Maybe the 60mm will be more beneficial.

That is the guide scope I am using on my system listed below. It is mounted on a ADM D to V mount. I installed a D rail on top of my scope. The ADM mount is heavy but worked fine for my EQ mount.




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