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Plan of action for AP?

catadioptric dso SCT
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#1 Kinguin

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Posted 28 November 2020 - 01:43 PM

Hello everyone,

 

So i am currently thinking of buying an SCT 8' and i have as a final goal to take photos of DSOs. I know the saying "SCTs are no good to start AP" but i think i have a plan.

 

Currently i am mostly going to use it for visual purposes only. Then when i believe i am ready i'll move on to planetery AP in order to get used to the whole tracking,imaging and processing thing. Once i am getting acceptable images i'll get a 0.7 focal reducer and move on to the deep sky AP. The reason for that 0.7 focal reducer is to get as much forgiveness as i can from tracking errors etc. Then after (i suspect) quite some time i'll remove the focal reducer and start to utilize the max power of the SCT. 

 

What i want your opinions on is the following:

 

1) Will this help me to flatten the curve of learning deep sky AP?

2) Is this a good plan? Any other suggestions?

 

Thanks in advance.

 

 



#2 gatsbyiv

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Posted 28 November 2020 - 01:55 PM

Deep-sky processing is completely different from planetary processing, so I don't think your processing skills will carry over much.  You'll definitely get used to your equipment, though.  

 

Even with the 0.7x reducer, it's not an ideal beginner's setup for deep-sky AP.  You can certainly do it (and probably produce some nice images), it's just that your deep-sky imaging experience might be less frustrating with a small refractor.  



#3 dhaval

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Posted 28 November 2020 - 01:56 PM

I have nothing against people starting with long FL scopes, in fact, I would encourage it assuming you know what you're getting in to. If that is the case, the 8in can serve as a multi-purpose scope. 

 

That being said, an 8in isn't exactly great for planetary AP, for planetary, you should really think 11" and above. That obviously will mean that you should have a decent mount if you go with a GEM (you can get decent planetary done with a DOB as well).

 

Where I am going with this is, you ought to think about two scopes - one for visual/planetary and one for DSO. If you do down that path, then you may be able to get a lot of DSO work done using a smaller, less forgiving scope (it does seem from your post that you are worried about a long FL scope - it is a genuine concern, but if that is bothering you, you should not venture there, unless you like the challenges of imaging with a long FL scope and a 0.7x reducer is not going to change a whole lot in that regard). 

 

Think through it - from a cost standpoint, assuming you do it right, you might not be that different from a cost standpoint. 

 

CS!



#4 idclimber

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Posted 28 November 2020 - 02:10 PM

If you also eventually plan AP at least get a good mount.



#5 Kinguin

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Posted 28 November 2020 - 02:18 PM

I have nothing against people starting with long FL scopes, in fact, I would encourage it assuming you know what you're getting in to. If that is the case, the 8in can serve as a multi-purpose scope. 

 

That being said, an 8in isn't exactly great for planetary AP, for planetary, you should really think 11" and above. That obviously will mean that you should have a decent mount if you go with a GEM (you can get decent planetary done with a DOB as well).

 

Where I am going with this is, you ought to think about two scopes - one for visual/planetary and one for DSO. If you do down that path, then you may be able to get a lot of DSO work done using a smaller, less forgiving scope (it does seem from your post that you are worried about a long FL scope - it is a genuine concern, but if that is bothering you, you should not venture there, unless you like the challenges of imaging with a long FL scope and a 0.7x reducer is not going to change a whole lot in that regard). 

 

Think through it - from a cost standpoint, assuming you do it right, you might not be that different from a cost standpoint. 

 

CS!

 

 

I believe i am aware where i am getting into with SCTs and i already have realised that at first i'll probably be happy if i manage to get any signa at all. I don't expect to plug in a camera and take those breathtaking images so overall i have my expectations low. I see you use a rig with an Edge HD scope. What if i invest in one of them and use them in the RASA configuration. I know that if i go that route i'll need a dedicated CCD and not a DSLR but even then price wise i think it'll come again pretty much the same with the overall price from bying a decent APO refractor together with a SCT.



#6 Stelios

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Posted 28 November 2020 - 02:19 PM

For visual, an 8" SCT is a great scope.

 

For planetary AP, an 8" SCT is an adequate but not great scope, you want ideally more focal length than that. 

 

For DSO AP, there are several things you need to consider:

 

First and foremost, there are the regular SCT's and then there are the Edge HD's. It is the Edge HD's that offer flat fields and take the 0.7x reducer, also are Hyperstar capable. Those additional capabilities don't come cheap though. 

 

Second (but first, really, in importance) is the mount required. For visual or planetary AP, a lowly AVX will be quite adequate, not only for an 8" but even larger SCT's. But for DSO AP, you want an EQ6R-Pro at a minimum (CGEM is not of the same quality).

 

Third--even with the proper mount and the reducer, you will need to guide with an OAG (off-axis-guider), and still it will be very, very hard. 

 

Fourth--unless you get a $1,000+ Hyperstar add-on, you will be limited to smaller objects. No Andromeda, Heart Nebula, California nebula, etc. for you.

 

So overall, the plan is great as far as visual and planetary AP is concerned, but breaks down when it comes to DSO AP. It breaks down even worse because nothing you will have learned in planetary AP will be useful--neither acquisition nor processing. Perhaps finding targets and focusing. 



#7 Kinguin

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Posted 28 November 2020 - 02:27 PM

For visual, an 8" SCT is a great scope.

 

For planetary AP, an 8" SCT is an adequate but not great scope, you want ideally more focal length than that. 

 

For DSO AP, there are several things you need to consider:

 

First and foremost, there are the regular SCT's and then there are the Edge HD's. It is the Edge HD's that offer flat fields and take the 0.7x reducer, also are Hyperstar capable. Those additional capabilities don't come cheap though. 

 

Second (but first, really, in importance) is the mount required. For visual or planetary AP, a lowly AVX will be quite adequate, not only for an 8" but even larger SCT's. But for DSO AP, you want an EQ6R-Pro at a minimum (CGEM is not of the same quality).

 

Third--even with the proper mount and the reducer, you will need to guide with an OAG (off-axis-guider), and still it will be very, very hard. 

 

Fourth--unless you get a $1,000+ Hyperstar add-on, you will be limited to smaller objects. No Andromeda, Heart Nebula, California nebula, etc. for you.

 

So overall, the plan is great as far as visual and planetary AP is concerned, but breaks down when it comes to DSO AP. It breaks down even worse because nothing you will have learned in planetary AP will be useful--neither acquisition nor processing. Perhaps finding targets and focusing. 

I see what you mean. Overall as i mentioned i have my expectations low but thanks for the analysis. I apreciate it 



#8 idclimber

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Posted 28 November 2020 - 02:36 PM

I started AP with a 12" SCT I already had at the beginning of this year. I quickly added a refractor based on advice here. I greatly prefer imaging with the refractor even though my SCT is extremely well fitted for AP on an extremely capable mount. It has noting to do with one being suitable for a beginner or being easier. It simply takes better images. 



#9 dhaval

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Posted 28 November 2020 - 03:44 PM

I believe i am aware where i am getting into with SCTs and i already have realised that at first i'll probably be happy if i manage to get any signa at all. I don't expect to plug in a camera and take those breathtaking images so overall i have my expectations low. I see you use a rig with an Edge HD scope. What if i invest in one of them and use them in the RASA configuration. I know that if i go that route i'll need a dedicated CCD and not a DSLR but even then price wise i think it'll come again pretty much the same with the overall price from bying a decent APO refractor together with a SCT.

RASA or an EdgeHD at F2 are specialized imaging instruments. I would not recommend those to people who are not experienced. Using these instruments, you run in to a lot of more challenges around collimation, tilt, etc. - on top of things like guiding, calibration, etc. 

 

CS!


Edited by dhaval, 28 November 2020 - 03:47 PM.


#10 ryanha

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Posted 28 November 2020 - 03:48 PM

I think everyone's journey is different.  I can say that for me I did exactly the journey that you are talking about.  I got a hyperstar-capable Celestron 8" (though not the edgeHD).  I started with planetary imaging then went to DSO.  I am no expert, but have been pretty happy with my results 6 months in (link to my astrobin).  I decided against using Hyperstar, but that is a different thread/discussion.

 

That said, there were many, many challenges along the way that I spent way, way, more time (and $$) solving than I had expected to do smile.gif  I don't regret for a second going this path, but I think "eyes wide open" is important.

 

Couple things to go through:
 

 

Learning on planetary: Processing and tracking are completely different than DSO.  Planetary you do not use a guide scope, you track using software like FireCapture that looks at the image and nudges the mount to keep it in frame.  Also processing for planetary is all about "lucky imaging" where you take 100fps and then filter for the best then stack and sharpen.  That all said, there is a lot to learn that translates.  ASCOM, cameras, mount stuff, patience, frustration, etc. smile.gif

 

Target size:  Personally with the focal reducer I love the FL that I am at.  I love the targets and the framing that I get.  It is true I can't do wide field, but for me (personal taste) I am more excited about the smaller targets than the larger targets.  You can go to telescopius.com and enter some telescopes and sensors and do searches for the types of targets you would see based on options.  Then you can search astrobin for those targets to see good examples of them.  You definitely should understand the different types of targets just so you are not surprised by what you can (and can't) do with the gear you get.  Here is a link to my Astrobin with planetary and DSO targets on my 8" (link).

 

Scope size (8" for planetary?): Planetary imaging is mostly limited by seeing (e.g. where you live and the atmosphere).  An 11" won't make your seeing better.  That said, absolutely it is true that a larger aperture for planetary if seeing is good will produce better results.  That said, here is a great thread from the planetary forum on 8" results (link): 

 

EdgeHD:  For me, the flatness of the edge is pretty subtle and not something I personally am concerned about (personal opinion).  Here is a thread showing an example of the coma that you can see with non EdgeHD frames (link).

 

 

 

In summary, if you are the kind of person that can dig into technical details and be patient and sift through challenging diagnostic situations, AND if you like the targets you can see with the 1200 - 2200 FL scopes, by all means this is a great path.  However if you like wider field targets OR if you are not super technical or patient, then SCT to start could be a recipe for giving up.

 

Either way, this is a great community of people here who can help when you get stuck.  I am 100% sure that without CN and a couple other forums I would have given up by now for sure.

 

Thanks,

--Ryan


Edited by ryanha, 28 November 2020 - 03:51 PM.


#11 RedLionNJ

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Posted 28 November 2020 - 03:52 PM

Unless you can get an 8-inch SCT with a primary mirror lock, DSO imaging is going to be an extended lesson in frustration.  Focus is going to shift and guiding is going to be a nightmare at first. Frustration levels will run very high and you may eventually invest in an 80mm class refractor, for the wider field, faster f-ratio, ability to guide better and more static focus.

 

So many of us have been there, failed or given up on path one and now own two scopes - a large SCT for planetary and a small APO for DSO.  Anticipate joining the club.  

 

Learning from the mistakes and successes of others is what sets mankind apart from the rest of the animal kingdom.



#12 DJL

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Posted 28 November 2020 - 04:01 PM

I was looking at getting an 8" approx SCT until I actually did a virtual astrophotography tour in Stellarium and realized the magnification would be too high for a lot of objects of interest. For now I have an 81mm refractor and while I don't rule out an SCT in future there is a lot to learn and do before then.

 

Make a list of the objects you want to observe, enter your candidate cameras and optics and then click through them and see how they look. Here are M42, M45 and M31: top row is WO GT81 with 0.8x reducer, bottom row is C8, camera is APS-C in all cases. The C8 gives dramatic closeups but you can't get the whole object in the frame without mosaics.

 

 

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