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IC 5070 Pelican Nebula

Posted: Tue Sep 11, 2018 10:25 pm
by turfpit
_IC5070-60x60s-g300-bl100.jpg (201.8 KiB) Viewed 1464 times
Altair Lightwave 66ED, Celestron AVX mount, Altair 183C
All Star Polar Align (Celestron mount), focus Bahtinov mask, unguided.

SharpCap 3.1
60 x 60s, gain=300, black level=100
60 lights, 30 darks, 50 flats

Processed in Siril + GIMP 2.10 (40 minutes total)

This target is a candidate for my new Ha filter and some longer exposures.


Re: IC 5070 Pelican Nebula

Posted: Tue Sep 11, 2018 11:49 pm
by oopfan

I say we rename it the Pterodactyl Nebula.


Re: IC 5070 Pelican Nebula

Posted: Wed Sep 12, 2018 12:27 am
by turfpit
Cheers Brian. A tricky one to dig out of the stack - some changes needed to capture settings.
Test frame below - the methodology seems to be holding up..

IC5070-FITS-image-statistics.jpg (99.61 KiB) Viewed 1456 times

Re: IC 5070 Pelican Nebula

Posted: Wed Sep 12, 2018 8:31 pm
by mAnKiNd
Very nice work Dave! Loving those textbook histograms :)
turfpit wrote:
Tue Sep 11, 2018 10:25 pm

All Star Polar Align (Celestron mount)
Just curious, do you carry out ASPS in conjunction with SC plate-solving for each alignment point? I tried that once and it builds up the model quite efficiently. However, I then started selecting Quick Align (assumes perfect PA) in the Nexremote software and simply used a planetarium like Cartes du Ciel to slew around and plate solve.


Re: IC 5070 Pelican Nebula

Posted: Thu Sep 13, 2018 9:02 am
by turfpit

At home, the Celestron AVX mount is sat on a fixed pier (bolted to a 2' x 2' x3' deep block of concrete). When at my dark site, I use the AVX tripod.

[Note: for clarification to others reading this post, All Star Polar Align (ASPA) is a facility built into the Celestron mount firmware to enable pole star alignment without having sight of the pole star. I used the function with success on my previous mount - a Celestron CG5 Advanced GT. Other manufacturers' mounts will have similar functionality I imagine.]

This is my workflow for DSO imaging:
  • Before full dark, align red dot finder and telescope with eyepiece on a distant land based object. I use a lit tower building about 1 mile away.
  • Swap the eyepiece for reducer and camera and check red dot finder and scope alignment on the laptop with reticule enabled. At this point no additional changes are necessary in the optical train except for addition of filters (I use a filter tray). This avoids those nasty optical shifts when changing the optical train.
  • Use the mount's polar scope for initial polar align. This is never far off as the pier is very fixed.
  • Carry out mount alignment as 2 alignment stars + 4 calibration stars. This is done using the red dot finder and camera capture. By the 2nd calibration star I am no longer needing the red dot finder as the target star is landing in the camera view.
  • Select suitable star (using Deneb recently) and carry out Polar Align procedure from Nexstar+ handset.
  • Focus with Bahtinov mask, selecting a star near to the object of interest.
  • Slew to object of interest.
  • Adjust capture settings (gain, offset, exposure).
  • Capture a single frame.
  • Mini histogram stretch and centre object if necessary.
  • Inspect single frame in FITS Liberator (see image in post above), looking for good histogram shape, Image Statistics Min > 0 and Max < 65535 which means no histogram clipping.
  • Repeat above step with different settings if histogram, Min, Max not acceptable.
  • Initiate capture sequence.
The Polar Align report from the handset looks like this:
PA-report.JPG (31.14 KiB) Viewed 1414 times

I am regularly hitting a last figure of 0" for both Alt and Az, with sometimes one or the other at 1". The above procedure, with persistence and practice, now takes me around 15 - 20 minutes and will define the success or failure of the imaging session.

After the ASPA, I suppose I should redo the alignment but I have been getting decent results for 60x60s unguided.

Why do I do PA this way?
  • I might be using an alternate capture program which does not have built in PA e.g AltairCapture.
  • I might be imaging mobile and in a location where the Pole Star is not visible - I have tested this.
  • I might be capturing using another operating system e.g. I have a Raspberry Pi 3 project in the pipeline, that puts me on Debian Linux.
  • I am getting full value and functionality from the £££s invested in the mount.
  • Until recently, I did not have a guide scope. I now have a QHY miniguider.
The two main issues I see on the forum relating to the PA procedure are:
  • Cannot solve because of finder scope limited FOV.
  • Cannot solve because of equipment flexure.
Neither of these apply when using ASPA.

Next two projects in my imaging development are guiding and planetarium software linked to handset for plate solving - PHD2 and Cartes du Ciel are candidates for this.

I have proceeded slowly in order to reduce complexity (old sysadmin habits kicking in here) and at each stage ensured that I have fully understood and am getting 'full value' from a facility before adding in another layer of complexity. I have been called pedantic in the past. I have seen too many posts where people pile on functionality, end up with a complex system that doesn't work and then spending more money on 'better' equipment - been there done that, stopped doing it.

I think my recent images posted in the Gallery Forum are leaving me feeling the above approach has been right for me, however, I would say to others YMMV.


Re: IC 5070 Pelican Nebula

Posted: Thu Sep 13, 2018 12:24 pm
by mAnKiNd
Hi Dave,

Thank you for the taking the time to explain your workflow, which sounds like textbook procedure and surely leads to great results, as you've demonstrated :)

I can only add comments from my experience and hopefully I can be of help. I've followed a similar workflow as yours as well when traveling to a dark site, but found the following to help reduce setup time and also PA accuracy is more accurate (since the zero values in the Nexstar remote are theoretical based on your input - but can still be very accurate. To really get them spot on you'd need the starsense accessory, which plate solves and gives you an actual PA error readout on the controller).

Here are my steps for alignment with the AVX

1. Rough PA with Polarscope

2. Confirm PA with SC (I use the imaging scope but if your focal length is high you can use the guidescope)

3. Connect Nexstar remote to PC and fire up Nexremote (newer controllers have the USB port)

4. In Nexremote, select quick align, which assumes perfect PA to base it's go-to slews and does not perform any subsequent alignment steps. This assumption is ok, since as we'll see below, plate solving will ensure that the go-to will align correctly.

5. Connect Cartes Du Ciel (or your own choice of planetarium) to Celestron ASCOM driver and slew to any target. You can even use the Nexstar remote handset or Nextremote on your PC to slew to your target, doesn't matter as long as RA DEC coordinates are communicated by ASCOM

6. Plate solve target in SC and enable sync mount

7. Begin adjustments to initiate maging that target and then start imaging

8. When finished with the target, slew to another, plate solve and repeat.

I find this approach faster and more accurate, as it has me setup and up and running to step 6-7 above in about 5-10 minutes, so about half the time.

I've adapted to this workflow whenever I have a PC irregardless of whether I'm in the backyard or at a dark site. The closest I got to the above without a PC was using the Starsense accessory with my AVX, but because I've yet to find a faster more accurate workflow, I always make sure I have my PC with Sharpcap on it when I setup.

Hope this helps

Re: IC 5070 Pelican Nebula

Posted: Fri Sep 14, 2018 12:18 am
by turfpit

Interesting. Starsense = ~£300 :( but has a lot of functionality. I like the idea of halving the setup time - I must look into that.