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Astrophotography with a Sky-Watcher Flextube 400P

Astrophotography Dob
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#1 rsliva

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Posted 09 December 2023 - 12:09 PM

I've been doing astrophotography for about 15 months using either an ES ED127 or a Celestron C11 on an EQ6-R Pro mount. Everything is run from a Beelink mini PC including N.I.N.A. to manage the session, PHD2 to guide, and ASTAP to solve. I've had good success and post my photos on Mastodon https://astrodon.social/@rsliva. After watching the video "Deep Sky Astrophotography with a Goto Dobsonian" (https://www.youtube....h?v=ypheEr4Vv-8) I was inspired to try astrophotography with a large 16" scope. So last month I acquired an SW Flextube 400P as a new astrophotography challenge and I wanted to share a little about my experience so far. None of this is new information.

 

My camera is an ASI2400MC-P and is fairly heavy. I also have attached a ZWO Duo-Band filter. I removed the focuser knob assembly, turned it around, and attached a ZWO EAF auto focuser. And I use a light shroud. With the tube now well out of balance (!) I have twist-tied a 2.5lb weight on to the mirror cell in back. It could use another pound, and magnetic weights would probably be better, but funds.... I am still using the Beelink mini PC, and it sits on the base next to the AZ motor. The motor controller on the side of the mount has a port for the Synscan handheld, but instead I use a Sky-Watcher serial-USB adapter that plugs into that port and the Beelink. And of course the camera and EAF also plug into the mini PC.

 

The Beelink is headless and I access it through Windows RDP (remote desktop). The key for me to automating the mount for astrophotography is the Synscan Pro App and the ASCOM driver that are both available for download from the Sky-Watcher website. The Synscan App drives the mount, and N.I.N.A. controls the app through the ASCOM driver. Note that I also use Cartes du Ciel to manage my targets and it also connects to the ASCOM driver. So once I RDP into the mini PC I start the Synscan App first and do a North Level alignment. I have found that the more accurately I level the mount, point it to true north, and center the stars during the alignment process the better the scope tracks. And to be honest, it tracks AMAZINGLY well.

 

I do not have a guide scope and do not try to guide, but instead I setup the task in N.I.N.A. to take short exposure (4s-15s) and to check for drift every few minutes and re-center if needed. It appears that the re-center will fail (nothing happens) unless the target is at least 5 arc-minutes from center. The short exposures are also needed to avoid field rotation. I use ASTAP to stack since there are often 200-600 exposures per target to stack with such short times, and ASTAP is fairly fast.

 

I am having good success so far and continue to learn more after each session, but one challenge has really stumped me. I have a power strip on the base that the mount, camera, and Beelink are plugged into, and that power strip is connected to an extension cord into the garage. But as the mount turns in the AZ direction the power cord is pulled around one way or the other and I have to monitor it carefully to avoid tension that affects tracking. A portable battery pack would solve that problem but I'm not sure about the added weight to the system.

 

Please check out the Mastodon link above for some of my other photos. Thanks for listening and let me know if you have any questions.


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#2 smiller

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Posted 09 December 2023 - 01:06 PM

Hi Roger,

 

I’m glad you are having success.   I did the presentation in that video by the way, so I’ll feel responsible if you weren’t successful!  Lol…

 

Anyway, to your question on managing cables.   I do two things:

 

1) I have a battery on the base that I use for some of the connections (fan, scope power), but I still have three cables to the scope that I need to manage:   Camera to computer, power strip to camera (as my battery isn’t very large), and scope hand controller to computer (as I’m not using Wifi).   In all three cases, I bought cable extensions so the cables can be longer.  I also have Velcro stations on the scope so I can attach the cables at key locations to minimize the chance of a snag.   Finally, I then lay enough cable in front of the scope that it can safely slew the required amount.

 

2) One other note that I found:  Sometimes my scope goes crazy and tries to do a near 360 when slewing.  I don’t know the reason why so I implemented a “kill switch” on the base and have two limiters that I place on the plywood my scope sits on.  If it tries to slew outside of my defined arc, it will shut off the scope.  It’s triggered twice in about 60 outings.  I documented how I made this in the latest “how to” guide I uploaded here:

 

https://drive.google...4r0IP6PbxA/view

 

Finally, I’m curious about your experiences in using the USB to Serial connector as others have tried.  I’ve read mixed stories, some love it, some found it unreliable.   I may want to give that a try as I know the app provides more options than the hand controller and I’ve read people were successful using N.I.N.A. and platesolving to do a “two star alignment” on two arbitrary regions of the sky, but I haven’t tried that myself and may not until summer when it’s warm out and I’m more comfortable fiddling with new procedures.  Perhaps if you documented your exact procedures and configuration steps, it would help others to replicate it… as it’s so easy to get one step wrong connecting together several systems like we often do in AP.

 

Also, have you tried the wifi option to the base?

 

A 16” scope with a full frame camera… that is a light bucket, if you continue to have success you will have incredible imaging productivity on the small to medium sized targets.  

 

Do you have a coma corrector yet?  (The nexus will turn that into a beast, but you will have some significant vignetting)

 

Cheers,

 

Steven


Edited by smiller, 09 December 2023 - 02:35 PM.


#3 rsliva

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Posted 09 December 2023 - 01:46 PM

Hi Roger,

 

I’m glad you are having success.   I did the presentation in that video by the way, so I’ll feel responsible if you weren’t successful!  Lol…

 

Anyway, to your question on managing cables.   I do two things:

 

1) I have a battery on the base that I use for some of the connections (fan, scope power), but I still have three cables to the scope that I need to manage:   Camera to computer, power strip to camera (as my batter isn’t very large), and scope to computer (as I’m not using Wifi).   In all three cases, I bought cable extensions so the cables can be longer.  I also have Velcro stations on the scope so I can attach the cables at key locations to minimize the chance of a snag.   Finally, I then lay enough cable in front of the scope that it can safely slew the required amount.

 

2) One other note that I found:  Sometimes my scope goes crazy and tries to do a near 360 when slewing.  I don’t know the reason why so I implemented a “kill switch” on the base and have two limiters that I place on the plywood my scope sits on.  If it tries to slew outside of my defined arc, it will shut off the scope.  It’s triggered twice in about 60 outings.  I documented how I made this in the latest “how to” guide I uploaded here:

 

https://drive.google...4r0IP6PbxA/view

 

Finally, I’m curious about your experiences in using the USB to Serial connector as others have tried.  I’ve read mixed stories, some love it, some found it unreliable.   I may want to give that a try as I know the app provides more options than the hand controller and I’ve read people were successful using N.I.N.A. and platesolving to do a “two star alignment” on two arbitrary regions of the sky, but I haven’t tried that myself and may not until summer when it’s warm out and I’m more comfortable fiddling with new procedures.  Perhaps if you documented your exact procedures and configuration steps, it would help others to replicate it… as it’s so easy to get one step wrong connecting together several systems like we often do in AP.

 

Also, have tried the wifi option to the base?

 

A 16” scope with a full frame camera… that is a light bucket, if you continue to have success you will have incredible imaging productivity on the small to medium sized targets.  

 

Do you have a coma corrector yet?  (The nexus will turn that into a beast, but you will have some significant vignetting)

 

Cheers,

 

Steven

Hi Steven - great video and the associated guide!

 

I started with WiFi but I was getting periodic issues where the Synscan App just refused to see the mount until I turned in on and off multiple times. And then later would lose it again. The serial cable setup just works. Also, I've had the "run away" scenario you are talking about, but it hasn't happened yet since I stopped using WiFi. Maybe a coincidence. I like the kill switch idea.

 

As for using the two star alignment with N.I.N.A., I've read that also, and also a multiple slew out and solve back scenario that seems to build a successful alignment model. I will try these at some point (and document if I succeed). Right now it's just manually slewing in the Syncan App while the camera is looping - meh.

 

I would like to get the corrector. And it sounds like I could go with a battery pack - worth a try. The other cables are managed okay.

 

Thanks again.



#4 smiller

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Posted 09 December 2023 - 02:53 PM

As you progress, I would also be interested how you compare and contrast using your three setups:

 

1) EQ6-R Pro with the ES ED127

2) EQ6-R Pro with the C11

3) 16" Goto Dob

 

Those are three very different setups and as you can expect, that 16" Dob being Alt/Az is radically different than either of the two equatorial systems.  Since I don't have an EQ system I can't compare and contrast the total end to end experience:  Setup time, ease of capture, imaging productivity, stacking and editing differences, final results.

 

Once you feel you have similar levels of experience amongst them, I would be interested in your comparison as right now I only recommend Dob imaging if you already have one, don't have an EQ system and just want to try to see what it does for you.  In other words, "I already have one or I'm going to get one for visual use and/or planetary/lunar AP anyway, so why not try some deep sky with it just for fun."

 

Oh, and I haven't used ASTAP as I've kind of settled on SIRIL as my primary go-to solution for stacking as it's so fast and there are some configuration options I put in the OSC scripts that reduce intermediate disk space requirements it needs while stacking.  But I'm curious about ASTAP, perhaps I should give it a spin?

 

For editing, I use a mix of PixInsight/APP/Affinity with the Xterminator plug-ins although I know SIRIL also has a few decent tools but there is only so much I can learn, or need to learn.

 

Cheers,

 

Steven




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