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MC90 guidescope

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#1 Nicole Sharp

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Posted 21 September 2021 - 09:24 PM

How well could a 1250/90 Maksutov-Cassegrain work as a guidescope?

Was considering to get the 90SLT plus AVX 700. I figure I would need to remove the Vixen-style dovetail bar and replace it with guidescope rings, and then clamp the rings onto the dovetail bar for the MC180. Not sure if the lengths will match for that though? Could there be a way to use an MC90 as a guidescope without needing to remove the dovetail bar?

This is specifically for on-axis autoguiding on Solar System objects, particularly for long-exposure photography of Solar System objects, both in the daytime and at night. Specific use cases might include the moons of Uranus (which are below the visual limiting magnitude for 180 mm), the infrared surface of Venus' dark side, and narrowband or spectroscopic imaging of Solar System bodies. I know a C8, CC8, or C9 would be a better choice than a C7, but a C8 would still likely benefit from being autoguided.

The main issue appears to be mirror flop compared to a refractor?

How well could a small refractor work for planetary/Lunar/Solar autoguiding as compared to an MC90, or would a Barlow lens have to be used?

There is also the payload of the MC180 plus MC90 on an AVX, but it sounds like the AVX could handle it. I figure using the long focal length for autoguiding might help with the larger moment of inertia for the MC180.

Edited by Nicole Sharp, 21 September 2021 - 09:24 PM.


#2 Nicole Sharp

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Posted 21 September 2021 - 09:37 PM

I also don't know if it is possible to autoguide on the partial disc of Venus?

I know Lunar/Solar autoguiding uses specific features such as craters or Sunspots.

#3 RedLionNJ

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Posted 21 September 2021 - 10:19 PM

You don't need a guidescope for anything in this forum (except perhaps Neptune, dwarf planets or minor planets). You can guide directly on the planet itself, using the capture application.


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#4 Mitrovarr

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Posted 21 September 2021 - 10:20 PM

There is also the payload of the MC180 plus MC90 on an AVX, but it sounds like the AVX could handle it. I figure using the long focal length for autoguiding might help with the larger moment of inertia for the MC180.

I don't see that payload working for autoguided long exposure. If nothing else, keeping the weight down would justify using a cheap small refractor to guide.



#5 Nicole Sharp

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Posted 21 September 2021 - 11:20 PM

You don't need a guidescope for anything in this forum (except perhaps Neptune, dwarf planets or minor planets). You can guide directly on the planet itself, using the capture application.

What software supports this?



#6 Nicole Sharp

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Posted 21 September 2021 - 11:24 PM

You don't need a guidescope for anything in this forum (except perhaps Neptune, dwarf planets or minor planets). You can guide directly on the planet itself, using the capture application.

Except perhaps for spectroscopy?

 

Does this work for Solar features as well?  Or for the phases of Venus?

 

I don't see why Neptune wouldn't work if the software allows guiding using the imaging camera.  I didn't think this was possible?


Edited by Nicole Sharp, 21 September 2021 - 11:34 PM.


#7 Jaimo!

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Posted 22 September 2021 - 06:27 AM

FireCapture has autoguiding.

 

https://youtu.be/hoNJq_YmEtk

 

But when taking video, the exposures are so short I don't bother.  I only auto guide for deep sky, which makes a huge difference.



#8 Nicole Sharp

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Posted 22 September 2021 - 07:03 AM

FireCapture has autoguiding.

 

https://youtu.be/hoNJq_YmEtk

 

But when taking video, the exposures are so short I don't bother.  I only auto guide for deep sky, which makes a huge difference.

 

The video says that FireCapture cannot be used for Lunar or Solar autoguiding.

 

So what would be the best guidescope to use for planetary, Lunar, and Solar autoguiding with a 2700/180 MCT on a Celestron Advanced VX mount?  It seems like a small Mak would work better than a small refractor, unless the refractor was Barlowed?



#9 Jaimo!

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Posted 22 September 2021 - 08:10 AM

The video says that FireCapture cannot be used for Lunar or Solar autoguiding.

 

So what would be the best guidescope to use for planetary, Lunar, and Solar autoguiding with a 2700/180 MCT on a Celestron Advanced VX mount?  It seems like a small Mak would work better than a small refractor, unless the refractor was Barlowed?

Perhaps your solar question could be better answered in the Solar Forum.


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#10 RedLionNJ

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Posted 22 September 2021 - 09:39 AM

The video says that FireCapture cannot be used for Lunar or Solar autoguiding.

 

 

And this forum is not for discussion of lunar or solar imaging. It IS for planetary, which FireCapture excels at.


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#11 Nicole Sharp

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Posted 22 September 2021 - 09:55 AM

And this forum is not for discussion of lunar or solar imaging. It IS for planetary, which FireCapture excels at.

 

Can FireCapture autoguide on the phases of Venus or Mercury?



#12 Nicole Sharp

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Posted 22 September 2021 - 10:03 AM

And this forum is not for discussion of lunar or solar imaging. It IS for planetary, which FireCapture excels at.

 

I still don't understand how you can use the same camera for guiding as well as for imaging??  I thought that was impossible?

 

Most people are using short exposures for planetary imaging.  Does FireCapture still autoguide without a guidescope for long-exposure planetary imaging?

 

What about for planetary spectroscopy?

 

Someone else posted a similar question earlier, so forked there:

 

https://www.cloudyni...ain/?p=11379216



#13 Jaimo!

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Posted 22 September 2021 - 06:42 PM

You do not need a guide scope for Planetary, Solar, or Lunar. 

 

You need to research "Lucky Imaging".  Unlike deep sky imaging where autoguiding in a must, because the objects are so faint it requires multiple minute sub frames.  The Solar System objects listed above are so bright you will have exposures in the single millisecond range, guide scopes cannot guide at this rate.  

 

And if you want to know about spectroscopy you will need to go the Scientific Amateur Astronomy sub forum as this is off topic here.



#14 Nicole Sharp

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Posted 23 September 2021 - 04:30 AM

You do not need a guide scope for Planetary, Solar, or Lunar.

 

You need to research "Lucky Imaging".  Unlike deep sky imaging where autoguiding in a must, because the objects are so faint it requires multiple minute sub frames.  The Solar System objects listed above are so bright you will have exposures in the single millisecond range, guide scopes cannot guide at this rate.  

 

And if you want to know about spectroscopy you will need to go the Scientific Amateur Astronomy sub forum as this is off topic here.

Planetary autoguiding would specifically be for long-exposure photography, not short-exposure lucky imaging.  Specific examples would be for faint moons, narrowband imaging, spectroscopy, and infrared imaging of Venus' dark side.  Imaging the surface of Venus is the most difficult, and would require very long exposure times (likely minutes), especially with an MCT.  Less than 1/100,000 of the infrared light emitted by the Venusian surface is visible at 1050 nm.

 

If FireCapture supports planetary autoguiding while imaging using a single camera, without needing a guidescope, the main question is whether it can autoguide on the partial phases of Venus and Mercury.  For long exposures in infrared light on the dark side of Venus, the illuminated part of Venus will be severely overexposed.

 

Likewise, any long-exposure photography of planets to capture faint moons will overexpose the planet.

 

It sounds like any exposures of over 30 seconds for an AVX 700 will require autoguiding.


Edited by Nicole Sharp, 23 September 2021 - 04:37 AM.


#15 Jkaiser3000

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Posted 23 September 2021 - 05:58 AM

It is my understanding firecapture uses the video stream to measure how the planet is drifting and send corrections to the mount directly. This is due to the short exposures during video capture so you can use two consecutive frames, measure drift and react accordingly. That process would likely not work for long exposures as you require. You will need two different cameras. Your mc90 would likely make a nice guidescope, provided you find a way to mate it to your main, imaging scope. The benefit with this approach is you can use the mc90 with a planetary camera and firecapture to guide and image the planet at the same time you use your main scope and long exposure camera to capture the intended target. Sort of a comparison if you will, or maybe an overlay or double exposure of sorts. 
 

can’t wait to see what you get out of it. Planetary spectroscopy and narrow band imaging sound quite interesting to me.


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#16 Nicole Sharp

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Posted 23 September 2021 - 09:27 AM

It is my understanding firecapture uses the video stream to measure how the planet is drifting and send corrections to the mount directly. This is due to the short exposures during video capture so you can use two consecutive frames, measure drift and react accordingly. That process would likely not work for long exposures as you require. You will need two different cameras. Your mc90 would likely make a nice guidescope, provided you find a way to mate it to your main, imaging scope. The benefit with this approach is you can use the mc90 with a planetary camera and firecapture to guide and image the planet at the same time you use your main scope and long exposure camera to capture the intended target. Sort of a comparison if you will, or maybe an overlay or double exposure of sorts. 
 

can’t wait to see what you get out of it. Planetary spectroscopy and narrow band imaging sound quite interesting to me.

 

Thank you very much for this explanation.  I couldn't figure out how they could autoguide and image using a single camera.  I figured if that was possible, no one would buy autoguiders or guidescopes.  It only works for short exposures then, since it uses alternating frames for imaging versus guiding.  Very clever to be able to do that, but since I want autoguiding for long-exposure planetary and Solar imaging, it won't work and I still need a guidescope.

 

I already own a 1000/90 MCT, but I need a portable tracking mount for eclipses, so was thinking to get the 90SLT plus AVX 700.  However, with both a 1000/90 MCT and a 2700/180 MCT, I am concerned that the 1250/90 MCT might end up being redundant and perhaps useless if I can get the 127SLT instead of the 90SLT (1500/127 would be more useful as an intermediate MCT between 1000/90 and 2700/180).  But if I can use the 1250/90 MCT as a guidescope for the 2700/180 MCT, then that would make purchasing a 90SLT plus AVX 700 more cost-effective, since I don't want to remove the dovetail bar from the 1000/90 MCT if I don't have to (this is my preferred 'scope for full-disc Solar and Lunar imaging with APS-C).

 

My primary concerns are mechanical, i.e. a) weight and b) length.  I am thinking that the 2700/180 MCT plus the 1250/90 MCT on guide rings might end up being about 25 pounds (out of 30 pounds for the AVX), but not sure how well that will work for long exposures at 2700 mm of focal length.  The other concern is that the guide rings would have to be clamped onto the MC180 dovetail bar, and I'm not sure if there is enough length on the dovetail bar for that.  Otherwise a piggyback or side by side would be needed instead, which could increase the weight and/or flexure.

 

The alternatives I figure would be using a more traditional guidescope on the finder shoe, or a small refractor on guide rings, but I don't know if that would need to be Barlowed for planetary autoguiding at 2700 mm of focal length.  For a native focal length longer than a small refractor but a smaller weight than an MC90, there is also a 700/60 MCT available from Omegon (only 1.3 pounds).  Traditional guidescopes want a wide field of view and a fast focal ratio to find guide stars, but that shouldn't be necessary for on-axis planetary autoguiding (only one bright object in the center of the field of view).

 

I am assuming that the MC90 has to be on-axis with the MC180 for planetary autoguiding?  I think the 90SLT dovetail bar is 1/4-20 threaded, so it could be piggybacked but without guide rings or a guidescope mounting, it won't be on-axis with the MC180.

 

My question about FireCapture though still stands: does planetary autoguiding with FireCapture work for the phases of Venus and Mercury?  A shorter focal length would make them appear more pointlike, but might not be as accurate for guiding.


Edited by Nicole Sharp, 23 September 2021 - 09:41 AM.



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