Pelican with strange artefacts

[Padraic M]

Hi all, I took some luminance frames of the Pelican Nebula last weekend while waiting for Pacman to come into view. Got 1.5 hours mono with a Thousand Oaks UHC filter, stacked in DSS and processed simply in Gimp.

SW Esprit 80 w/ff; ASI1600MM 1x1 @-20C, gain 139; HEQ5 Pro unmodded, guiding with PHD2 and achieving 1" total RMS (imaging scale is 1.9"/px).
18x300s lights with darks, flats and dark flats calibration frames. The result is #1 below - not bad for my current stage of development, but the nebula itself is a bit noisy - possibly I've over-stretched what's there.

Some questions on exhibit #2 below - including two artefacts that I've masked out roughly in the first version:
- The 'tapioca' stars to the Pelican's left and right (56 and 57 Cygni I believe). The circular halos are present in the raw lights and become apparent early in the stretching process. Any idea what's causing them? All of the rally big stars have them, but they're not obvious on the smaller stars. They also don't look like the usual star bloat that comes from over-stretching. I have a dew heater on the imaging scope but not on the camera/filter wheel.
- The sun-beam coming in from the edge at 1o'clock. I am assuming that this is stray light from Deneb which is just out of frame in that direction. Any suggestions as to how to avoid this? I am using the stock dew shield on the Esprit 80.

 

[assouptro]

Hi Padraic 

I have had halos on bright stars for several  reasons:

1. Poor quality filters resulting in internal reflections 
 

2. internal reflections caused by badly coated reducers/flatteners

3. High thin cloud.

4. Dew, but you appear have cancelled this out.

5. Expired desiccant tablets in my cooled camera. 
I hope you get to the bottom of it, and well done for processing it out in image #1! 
I think you are right about the “sunbeam” 

Good luck resolving this! 
 

Bryan 

[kirkster501]

^^^All that Bryan says.  You need to eliminate this stuff.  Skies have been dire of late, even in the few "clear" nights that we have had and I had some subs like this and had to throw them out.  You have to be ruthless with subs ruined by cloud and maybe you haven't been?  The filaments of detail are extrenely fine in these nebulae and any loss of clarity can wipe it out. I also think your focus is slightly off, exacerbating any issues aforementioned.  There are many plates to spin and master in AP!!!  Not easy because to eliminate problems or work around them requires precious and rare clear sky time, that we'd rather be imaging/observing in, and not resolving problems!

Also, though I am not sure it applies here, the ASI1600 is well known for bright star artefacts.  Search on here for this.

 

Edited September 30, 2020 by kirkster501

[Padraic M]

Thanks Bryan @assouptro and @kirkster501. Report card says 'Must try harder'. There are so many factors to get absolutely right in this game. I'll check each of the subs for anomalies. DSS scored them all fairly equally; there didn't seem to be any cloud/fog on that particular night, but just because it was the best night for weeks at the moment doesn't say much. 

I've been considering a set of narrowband filters, or at least a good quality Ha, but it would be nice to find a problem that I can solve without spending lots of money (again) on kit. Maybe focus is an area to spend some more time on, in the next clear spell. 

 

[ollypenrice]

I think those hard edged halos are from internal reflection. I know that some CMOS cameras have been prone to them but I don't know which ones. It might be worth Googling your camera model to find out. I find high haze and dew give soft halos. (Edit, I see Steve has identified your camera as one that's known for it.)

The light house beam is from Deneb, as you suggest. I've had it as well! It is possible to mitigate this kind of thing by careful use of manual repairs in Ps but that is never more than a bodge. It was actually on Deneb that I came across the real way to solve the problem. A guest and I were working on a large North America mosaic and a panel corresponding to yours had the beam. However, the adjacent panel in which Deneb was in shot did not have it. Such beams are often created by out-of-shot stars so what you can try is a shot in which you've slewed as closely to Deneb as you can while still covering the part of your image with the beam. You don't need hours of data, just enough to layer in so as to tame the beam. This worked perfectly for us in the NAN mosaic and in repairing a horrible beam from Rigel in my Witch Head image.

Olly

Edited September 30, 2020 by ollypenrice

[alacant]

12 hours ago, Padraic M said:

circular halos

Hi

Why not just cheat?!

Cheers

[ollypenrice]

6 minutes ago, alacant said:

Hi

Why not just cheat?!

Cheers

Did you pull down hard-edged halos there, or soft ones? If they were hard-edged you did a darned good job!

Olly

Edited September 30, 2020 by ollypenrice
Typo

[kirkster501]

2 hours ago, Padraic M said:

Thanks Bryan @assouptro and @kirkster501. Report card says 'Must try harder'. There are so many factors to get absolutely right in this game. I'll check each of the subs for anomalies. DSS scored them all fairly equally; there didn't seem to be any cloud/fog on that particular night, but just because it was the best night for weeks at the moment doesn't say much. 

I've been considering a set of narrowband filters, or at least a good quality Ha, but it would be nice to find a problem that I can solve without spending lots of money (again) on kit. Maybe focus is an area to spend some more time on, in the next clear spell. 

 

Don't be discouraged - that is a good Pelican.  Think of all the things you got right!  You found it, framed it, tracked it.  A couple more pieces of the puzzle in place and you'll be firing on all four cylinders!  But focus.... that one is critical, all is lost without good focus.  Get a Bahtinov mask or make one.  Maybe your sky *was* ok?  I'm just saying that if you have fuzzy subs you need to bin them or grade them accordingly so they contribute less to the integrated image stack.

[Padraic M]

@ollypenrice thanks for that insight - the camera is the camera (just invested so I'm not going to change!) so if it's an issue there, I'll just have to work with it! There are lots of folk on here taking mighty fine pictures with that model so I'll research how they've dealt with it. It looks like the hard-edge halos are indeed a result of the microlensing 'feature' of this camera, so nothing to be done about that. I also notice that this particular UHC filter is VERY reflective on the camera side so that may be exacerbating the problem. I might try without the filter, but I'm in the city for the next few months with lots of light pollution so not too hopeful there. 

I love your solution for the Deneb beam. I'll get some frames the next clear night to use for patching. Clone/curves/smudge are only so good, but when you know where the beam was, you can never un-see it.

Possibly worth adding that there's very little else in the light path - Esprit 80 (quality a given?); Esprit field flattener (ditto); filter and camera. Nothing else. So if the scope, FF and camera won't change in the medium term, the filter is the only point in the light path open to experimentation.

Which brings me on to @alacant's suggestion - cheat! That's a great impression of the Pelican/NAN but you may have obliterated the home-worlds of countless civilisations! Two whole stars just gone. I'm going to save that away and use as a reference for future processing.

 

[Padraic M]

6 minutes ago, kirkster501 said:

that is a good Pelican

Thanks! Not discouraged at all, just pondering what best to attend to next, of all the various aspects of AP. Lesson #1 learned already: you feel under pressure to start capturing as soon as possible, to make the best use of the limited clear skies time; but better to spend an extra hour on getting the basics of alignment, tracking, focus etc. spot-on than get an extra hour of so-so lights.

But I am surprised about the focus. I used a mask and the APT Bahtinov aid and the figures seemed good. I need to tune up my own eyes to assess what is actually good focus in the image.

[ollypenrice]

34 minutes ago, Padraic M said:

Thanks! Not discouraged at all, just pondering what best to attend to next, of all the various aspects of AP. Lesson #1 learned already: you feel under pressure to start capturing as soon as possible, to make the best use of the limited clear skies time; but better to spend an extra hour on getting the basics of alignment, tracking, focus etc. spot-on than get an extra hour of so-so lights.

But I am surprised about the focus. I used a mask and the APT Bahtinov aid and the figures seemed good. I need to tune up my own eyes to assess what is actually good focus in the image.

I don't think you'll beat the figures by eye. However, focus can change quickly with temperature.

Olly