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Recommendations for Guiding Scope

Astrophotography Beginner Equipment
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#1 kbennett

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Posted 07 March 2021 - 02:30 AM

Hi all! 

 

I'm looking to get back into observing and astrophotography after a 11+ year break.  Before I go and spend countless dollars on a better mount, cooled camera, etc., I want to check on two things: 1) I can get decent long exposures with the equipment I have, and 2) that I can get decent long exposures from my location (suburbs of San Diego, SQM 18.47 mag./arc sec2, Bortle 7).  I know you can get amazing shots from places like this (or worse!) but I don't want to buy a bunch of stuff and be disappointed by my light pollution limitations...

 

First, the equipment I have:

10" LX200R, f/10

Milburn Deluxe Wedge

Meade DSI-II OSC (for imaging)

TIS DFK 21AF04.AS OSC (for guiding)

Supporting software (TheSky 6, PHD2, DSS, etc.)

 

In my previous efforts, I was never able to get anywhere above 30 second unguided subs, and most of those were marginal.  I was able to some decent planetary imaging with the DFK.

 

I'm looking for a guide scope that I can easily mount on my OTA.  I already have one rail on the bottom for counterweights, but I'm willing to put one on the top for the guide scope.  I got the rail with the counterweight system from Ken Milburn (same as the wedge) but I don't know if it's officially compatible with the Losmandy D style or Vixen style rail.  I know it's 1.5" wide, but that's all I know. The other option would be to replace the Meade 8x50 finderscope with the guide scope, if I can find a compatible mounting bracket.

 

I'm looking at two options right now.  Again, I'm trying to keep the cost down until I can convince myself that I can do this!  Here's what I'm thinking so far:

1) ASTRO-TECH 60MM PHOTOGUIDE REFRACTOR (or the alternate branded Astromania 60mm Compact Deluxe Finder & Guidescope)

2) Orion ST80 Refractor

 

My biggest concern is how to mount either of these scopes to my OTA.  The mounting bracket for the 60mm doesn't look like it matches the 8x50 finderscope shoe, and I don't know what kind of shoe or bracket I would need.  I suppose I could mount it with the rings holding the current 8x50 finder, assuming the OD is not too large.  For the ST80, I'm assuming I'd need to get rings, which seems to be no problem, but then how to mount those rings on the OTA? 

 

I like the idea that I could potentially image with the ST80 as well as guide, but the 60mm comes with the rings (if I can only figure out how to attach it...)

 

Any suggestions are greatly appreciated!  I'm also open to other ways to start guiding, but still trying to keep the cost down initially.

 

Thanks!

 

- Kevin



#2 james7ca

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Posted 07 March 2021 - 02:52 AM

IMO, that Orion ST80 won't work very well for astrophotography. Yes, it will produce an image but it won't be very well corrected (chromatic aberration and off-axis problems).

 

Those 60mm guide scopes are okay, but the most important issue with any guide scope is how rigidly it can be mounted to the main imaging scope. Plus, you have to be concerned about any flexure that may happen with the guide scope's focuser (which could be a problem with all of those that you listed, perhaps worse for the ST80).

 

Frankly, if you are going to use the LX200R (at f/10) for imaging then you probably want to use an off axis guider (OAG) rather than a separate guide scope. Unfortunately, OAGs have their own issues and you may have problems finding a good guide star with an OAG. But, if you can get a well-made OAG and if you can make it work (i.e. easily and reliably find guide stars) then that is the way to go with your LX200R.

 

Another thing to consider is to get a flattener/reducer for you LX200R. But, using a reducer may cause problems since that will restrict the amount of back focus you'll have when using an OAG (since reducers have spacing requirements and the OAG may make it difficult to achieve that spacing once you place the OAG between the reducer and the camera or between the reducer and any filters and the camera).



#3 Stelios

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Posted 07 March 2021 - 03:34 AM

Ditto on the OAG. Not only will you get better guiding than with the guidescope, but you avoid mirror flop and differential flexure issues. 

 

The Celestron OAG coupled with a good camera like the ASI174MM-mini (pricey but worth it) will solve all your problems. 

 

An ST-80 will be really poor as an imaging scope. It can be used as a guide scope. But... really, OAG is the way to go. All the problems with OAGs are solvable the very first session and an hour or so effort in advance (to get the two cameras to come to simultaneous focus). After that you don't need to do anything, ever, and it's all upside. 

 

I use OAG with all my scopes, even my little 70mm refractor. 


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#4 PederP

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Posted 07 March 2021 - 04:08 AM

In my opinion multistar guiding adds another factor to optimal focal length/ field of view when guiding.

Using an OAG with a .5 focal reducer could perhaps be a good middle ground?



#5 CoHPhasor

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Posted 07 March 2021 - 05:07 AM

I will get on the dog pile.
When looking at OAG, it will cost you.
Some OAG are cheap, ones you want not so much, and guide cams, same thing.

To increase the chances on having stars, you'll want a bigger sensor, to cover that sensor, you'll want a larger prism.
The focal length makes it hard for you to use a tiny one.
You pretty much want the "mini" guide cams like ZWO makes because they work well in helical focusers/drawing them in and out.
The asi120mm mini is attractive for price, but I advise against it - it isnt a proper match for your focal length.
I splurged and got the 174mm mini for my c11, but you may not want to spend that much.

#6 Phil Sherman

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Posted 07 March 2021 - 11:57 AM

Another option, if you decide not to take the recommended route and use an off axis guider, is to use a side by side mounting plate with a separate guide scope. When you switch to a different imaging camera, you can use the DSI II as a guide camera with PHD2.

 

Since you're getting back into imaging, you could also download Mike Unsold's now free "ImagesPlus"(IP) from his web site. IP will handle all of your image processing needs both for astro cameras producing .fits files and for older Canon and Nikon cameras which produce RAW files. There's some documentation for the program on Mike's web site and he also has many videos that demonstrate using the program's features.



#7 TxStars

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Posted 07 March 2021 - 03:33 PM

Off-axis guiding is going to be the best bet for prime or reduced imaging.

SCT mirror flop usually prevents the use of a guide scope.



#8 kbennett

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Posted 07 March 2021 - 06:28 PM

Thanks to everyone who's answered!  I appreciate the advice!

 

I actually do have an OAG (a Meade OAG) and my concern with it has been that mounting it after the microfocuser, the train hits the forks at the bottom.  Of course, I can always setup, basic align, and get good polar alignment without the OAG, and then add it on before imaging.  I don't think I'll be imaging right around the North Star too often!  lol.gif

 

Another concern I've had is worrying about getting the guide cam and imaging cam well focused at the same time.  The Meade OAG doesn't have a built-in focuser, so it feels like it would require a perfect match to get them the exact same distance for good focus.  But maybe I'm overestimating how perfect the focus needs to be for guiding?  Or are there other tricks to getting that focus? (Maybe a parfocal ring to adjust one cam out just enough..?)

 

Anyway, thanks for all the info so far, I'll definitely re-think the use of an OAG.  And I still want to try and make this work with what I've got before upgrading.  If this works like it should, then I have no problem looking into a better (thinner!) OAG, better guide cam, better imaging cam, etc.!



#9 CoHPhasor

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Posted 07 March 2021 - 10:23 PM

The focus is crucial.
You dont have to do it at night though. The cam and guide cam just need to be in sync.
Pick a terrestrial object in the day, focus the main cam, then focus the guide cam.

Someone here did it using a tree last week. lol


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