M42 and Immediate Vicinity - First LRGB Project!

[eshy76]

Hi everyone,

I've been lurking around this place and CN for about a year, ever since finding this incredible hobby and have picked up so much from the global astrophotography community. I'm ready to engage!

As I am sure with many others, M42 was the DSO that captured my heart and started my obsession with astrophotography; my heart still soars when Orion is in the sky!

So after having initially captured it in March with an unmodded DSLR, wide angle camera lens and startracker, I've been impatiently waiting to have a crack at it with a telescope...and other upgrades.

Here is my first completed LRGB project, including some Ha in red and lum. Shot in my back garden (I also now have a back garden, which I didn't do in March!) in Sutton a week ago. 3.9 hours total integration. Shot with William Optics Z73 + ZWO ASI1600MM-Pro + iOptron CEM25P + Astrodon filters. Processed in PI.

Blown core (rookie error) and residual noise issues after sharpening, but I'm happy for now.

Thanks for looking!

[PhotoGav]

Well, that is a mighty fine entrance! Congratulations on a lovely image and for finding your voice on the forum. As you know already, the depth of knowledge on here and the willingness to share is incredible and will be the main reason for your descent into total Astro-obsession over 2019!!! Enjoy your journey.

[eshy76]

Thank you Gav!  The obsession is already strong...I'm checking the 7-day forecast every day...met office cloud cover tab never too far away. Quite apart from the physical capturing techniques, which I love....gear upgrade options are always there and even though I should be spending the next clear night collecting more M42 photons, there are just so many amazing targets up there...

...I've got it bad. Long may it continue!

 

[SamAndrew]

Welcome, Great start  very surprising what can be done under chronic levels of light pollution; I'm not far from you over in Kingston with a similar setup.

[vlaiv]

Welcome!

Lovely image.

Core might be a bit blown, but it is not out of place - it is nicely processed and it does not detract from the image in my opinion. It is very bright after all.

[eshy76]

Thank you Sam and vlaiv for the warm welcome and compliments!

The light pollution is what made me go down the mono route - and I have the 3 main narrowband filters which will be put to good use! However, I was skeptical about LRGB (well mainly the L) due to the LP, but thought, just give it a go. I think it was the bright nature of M42 that was more of an issue than LP in the end - I used quite short exposures. 

The RGB subs at 15 seconds (unity gain and 30 secs for R) did not seem to blown out and the ADU was coming in at around 1400-1500 per sub, which seemed about right for efficient sky glow smothering subs for the ASI1600. The Ha subs at 250 secs (unity gain) were also coming in at 1400-1500 ADU, which again seemed correct, though the Ha stack was very bright in the end. 

However the L subs at 15 secs each were coming in ADU 3300-3500 and I could see the core would blow out...I think going much lower in sub length raises practicality issues (willing to give it a go though!), or I could lower gain for the L subs to 0. I do also have an IDAS D2 filter, but there seems to be an opinion that stacked filters (the IDAS would go in front of the L, not replacing it in the wheel) may lead to a softer image...

...so yes I do have angles for attacking the core...but as you say vlaiv, ultimately M42 IS bright. Decisions, decisions...

 

[vlaiv]

The simplest way to do it is by combining two sets of exposures. If you utilize this approach, then you can use "regular" exposure length for most of the image, and short exposures for only over exposed bits. You don't need many short "filler" subs since signal is already strong (strong enough to saturate) so SNR will be good on just a few filler subs.

Principle would be: regular image and let's say 5 minutes total of 10s subs (so 30 short subs, this depends on target brightness, but you can easily judge it). Both stacked to separate stacks and mixed in post processing - just create mask based on saturation and mix two layers based on this mask. It is easier for me to explain it in math terms on linear data than it is with this layer technique, but I know that many people prefer second approach. In math terms you need to multiply short exposure to compensate signal level for given exposure length and then replace pixels in main sub with filler sub if they are over certain threshold - like 80% of max value.

[michael.h.f.wilkinson]

Very nice start indeed

[eshy76]

Vlaiv - thank you for that! Capturing a few very short subs of M42 shouldn't be too taxing...

I tend to agree that the image currently is "consistent" the core IS bright and hence why the whole nebula is bright, so I would look to make only a subtle change - but I really appreciate the technique you've opened my eyes to - I use both masks and PixelMath, so appreciate the two-sided explanation!

[eshy76]

Thank you Michael! ?