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Multipurpose guiding equipment options?

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#1 JG-42N



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Posted 17 April 2021 - 12:11 AM

I'm a beginner thinking about trying guiding, but need to get as much use out of equipment as I can to justify it, so I need to find a reasonable compromise.  


What I have so far:

203mm / 800 mm FL scope and an APS-C DSLR with 4.3µm pixels.  I have a coma corrector and a 2.5X Barlow.  I'm using an Orion Sirius (EQ5) mount and can get decent polar alignment (still learning), but 30 to 60 seconds without the Barlow is about the limit so far.  I'd be happy to get to 2 or 3 reliably.


An ETX90 from way back that would be interesting to try for planets and the moon.


I have been using Backyard EOS for my camera so far, and have been reading up on PHD2 and NINA as that seems to be what I should be looking at next.


My location is Bortle 5 with a badly aimed sodium light about a half block away, but shaded directly by my garage.



I'm considering these:


ZWO178MC camera 2.4µm pixels:


• A mono camera is better for guiding accuracy.
• A mono camera or larger pixels makes for higher sensitivity. 


• It has smaller pixels than some others which gets me into a reasonable guiding ratio (Astrotools.com) when I Barlow the main scope out to 2000mm.
• It will work directly as a color camera for planetary use.  Smaller pixels help there too.


Astro-Tech AT60GS guide scope - 60mm / 240mm FL    This looks to be the same: Agena 60mm f/4 Precision Straight-Through Finder / Guide Scope with Helical Focuser


• Heavier than smaller guide scopes.


• Possibly could be used as wide field scope with the DLSR with no guiding. 
• Could be a decent, throw on a camera tripod grab and go for wide field visual.


I'm trying to keep in mind the limits of the equipment vs the limits of the operator.  There is no real point going with equipment way past my skill level.  I've done very little processing so far.


I doubt that I will be getting a better primary imaging camera down the road.  Cooled would be nicer than the DSLR, but I have a LOT of learning to do, and it is Iowa.  Seeing is often less than great.


So, with this in mind, please let me know what you think.  The camera and guidescope mentioned take me to my current budget limit, so this almost turns into a question of should I bother or should I wait.

One specific question is if anyone knows if the Astro-Tech scope has enough backfocus(correct term?) for the DSLR to work.  I can't find any specs on that.  I think the camera needs 55mm from the front of the T-adapter.



Thanks in advance for your comments,


Edited by JG-42N, 17 April 2021 - 12:20 AM.

#2 Tapio



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Posted 17 April 2021 - 01:07 AM

Sounds ok plan for guiding.
Another alternative is OAG but don't know if there's backfocus for it.


Those basic guide scopes are really not meant for imaging.
And especially not with DSLR with large sensor.
I know some have tried Skywatcher 50ED Evoguide, but that needs a flattener too.

PS Sirius mount is at the threshold of handling that kind of scope.

Edited by Tapio, 17 April 2021 - 03:37 AM.

#3 JG-42N



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Posted 18 April 2021 - 12:41 AM

Thanks for the feedback.  I have been reading about the differences in image scale between the guide and the imaging sides and this seemed like it should be usable, but I wasn't sure. Also, most every comment says only mono for a guide camera, but then there are a lot of color cameras that do guiding.  It's hard to separate the advertising from the reality.


OAG isn't something I want to do at this point.  Maybe down the road a ways.  I know that a guidescope will perform poorly compared to a real scope, especially with the large sensor, more of a curiosity question on that.   


I also know that the Sirius is marginal, but it was what I could do at the time.  Seemed to be an ok entry level choice.  I do what I can within budget and try to learn as much as I can before I buy, so I'm not surprised at the reality.  Mostly I'll be at 800mm, but would want to try longer with the Barlow from time to time.  I'm also in process with building a roll off roof obs, so that will help with wind.


Primarily, I'm a casual visual observer, but I like to learn new things, so thought I'd explore this direction a bit.

Edited by JG-42N, 18 April 2021 - 12:41 AM.

#4 AhBok



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Posted 19 April 2021 - 08:56 AM

If you use a guide scope a color cam is fine for guiding. A mono cam does not guide more accurately. A mono cam is is more sensitive and especially useful if you use an OAG with a narrow field of view (especially at longer focal lengths). The color cam can double as a planetary cam. You’ll get better planetary images with your main imaging scope and 2.5x Barlow than with the 90mm ETX. The EQ5 is a weak point, but you can learn the fundamentals with it. To continue to improve, you will need a better mount, but that decision is better put off until you get a bit of experience and better able to judge what your future purchases should be.

Good luck!

#5 JG-42N



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Posted 21 April 2021 - 12:24 AM

Thanks.  Always helps to hear what someone else says.  I see on Astrobin that you have guided and imaged with a QHY camera with the same sensor.  That is reassuring. Nice images!  


Getting a few images with the ETX is just because I should to be able to say that I did.  Focusing it is an exercise in patience...  It's also old, first version, so I'm sure the mirror has degraded some.


I have a lot to learn, but I'm getting a start.  

Edited by JG-42N, 21 April 2021 - 12:30 AM.

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