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Hi ladies & gents... can I use "ANY" small refractor for guiding ?

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#1 cc2014

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Posted 10 February 2019 - 10:27 AM

I was wondering if there is any recommendations or advice for a guide scope... there is a LOT in the market and surely they are "made for..." I have a William Optics Megrez 110 f/5.59 & Ioptron 150 6" 1800 ... hoping to get a scope that suit both !!! Thanks in advance !!! \m/



#2 jsmithsd

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Posted 10 February 2019 - 10:33 AM

Hello, what guide camera do you plan to use?



#3 cc2014

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Posted 10 February 2019 - 11:01 AM

I got the ZWO ASI290 at the moment



#4 Destrehan Dave

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Posted 10 February 2019 - 11:41 AM

The best one I have ever used... if you have a lightweight guide camera.

https://www.sciencec...rg/guidescopes/

DD
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#5 gnowellsct

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Posted 19 February 2019 - 12:10 AM

I don't image but the baader Vario gets good reports.  Check it out at Alpineastro.com or on the astrophysics web site.  Astro-physics doesn't mess around when it comes to imaging.  

 

My imaging friend tried "any small refractor" for his guiding and had a lot of problems principally with flexure.   Eventually he got the Baader vario and mount from astro-physics and ended up believing it inexpensive for what it did rather than over priced.  

 

But that's just him.

 

Greg N


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#6 macdonjh

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Posted 19 February 2019 - 12:37 PM

I don't image but the baader Vario gets good reports.  Check it out at Alpineastro.com or on the astrophysics web site.  Astro-physics doesn't mess around when it comes to imaging.  

 

My imaging friend tried "any small refractor" for his guiding and had a lot of problems principally with flexure.   Eventually he got the Baader vario and mount from astro-physics and ended up believing it inexpensive for what it did rather than over priced.  

 

But that's just him.

 

Greg N

Greg, I wonder if your story implies, much like with a main scope, that when dealing with astrophotography the mount counts for a much larger percentage of the results than the optics do?  I wonder if cc2014 can use "any small refractor" for his guide scope as long as he mounts it well?



#7 gnowellsct

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Posted 19 February 2019 - 01:09 PM

Greg, I wonder if your story implies, much like with a main scope, that when dealing with astrophotography the mount counts for a much larger percentage of the results than the optics do?  I wonder if cc2014 can use "any small refractor" for his guide scope as long as he mounts it well?

Well the problem is that "any small refractor" could be something with a lot of flexure in the focuser.  If "any small refractor" is something with a cheap focuser you might be sunk.  The extended mounting bracket of the Vario is clearly intended to address that issue.

 

I'm not an imager but I try to pay attention to at least some of the issues.  There was a LONG post in Yahoo C14 years ago about a guy that was trying to get flexure out of his guide scope.  It was an extremely difficult technical task and vital to the correct functioning of the corrections issued by the guide scope to the mount.  He was at it for months before  he finally had the system where he wanted.  

 

So I'm aware that this is a big deal.  When my friend got into imaging the Yahoo posts from years ago were re-enacted before me in real life, as it were, rather than some guy putting up posts.

 

I should note that I spent close to $2,000 evaluating which hardware would be best suited to mounting a refractor on an sct for *visual* use and my concerns were very different.  I have found that it is nearly impossible (a) to have the top mounted refractor exactly parrallel to the main tube and (b) have it stay that way as you move around the sky.  So ultimately I threw a lot of coin at systems that would allow for *rapid correction* of misalignment, which is different from preventing the misalignment.  If you're an imager you want to prevent the misalignment from slowly creeping in as you do your exposures.  A five arc second error is trivial for a visual observer but it' s a big deal for for an imager chasing those elusive round stars.  (I sold the hardware I didn't keep so I didn't net out at $2k)

 

But you can see that the engineering problem is the same.  As a non-imager rather than chase the chimera of a secondary scope that does *not* move I decided that it was better to accept that fact that it moves and make it easier to correct it.  But the imager who wants the secondary scope *not* to move needs, unlike me, to find a way to lock it down.  In both cases, however, we are dealing with the fact that the secondary scopes move and it's REAL HARD TO STOP.    

 

The problem is sufficiently difficult that some imaging people move to off-axis guiders and punt the secondary scope.  For visual you don't have to correct the tendency of the scope to move around, as I do.  You can let it move and use your mount to recenter the object in the secondary scope.  I'm pretty sure that's what folks who are using Losmandy style guide scope rings are doing.  That, and using very light weight secondary scopes that don't stress the system much.    Anyhow no matter what you do you're going to be dealing with flexure one way or another, even deciding not to deal with it means dealing with it by recentering objects in the secondary scope.  If you want to look at Saturn at high power in your refractor and also compare to the view in your C14 you either have to have the two scopes exactly parallel or you have to have the mount move back and forth, putting now one, and now the other, on Saturn in center field.

 

You're going to serve somebody, it might be the devil and it might be the lord, but you're going to serve somebody when it comes to flexure.   Anyhow when you've read what I've read and dealt with the various hardware I've dealt with and you see someone like AP marketing something that they say works, you pay attention.  It doesn't work *for me* though because I want to mount 80 to 102 mm secondary scopes which are much more of a challenge than the Vario guide scope which I think is 50 or 60 mm.

 

Greg N


Edited by gnowellsct, 19 February 2019 - 01:13 PM.

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#8 hfjacinto

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Posted 19 February 2019 - 01:23 PM

You can use "almost" any small or large refractor as long as its properly mounted. I currently use this:

 

https://agenaastro.c...cuser-60mm.html

 

But its mounts on a heavy duty focuser (either the APM one or the moonlite one)

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#9 hfjacinto

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Posted 19 February 2019 - 01:25 PM

I've also used an 80MM as a guider.

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#10 hfjacinto

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Posted 19 February 2019 - 01:27 PM

Here is the 60 on the 120 showing how secure it is.

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