Great Orion Nebula - 1st attempt

[R1k]

Very much enjoyed shooting this for the first time ever last night, keen to receive feedback as always

 

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Technical details:

 

Equipment:

- Skywatcher HEQ5-pro (Rowan Belt Mod)

- Canon 800d (modded)

- Skywatcher Evostar 80ED

- Altair Lightwave 0.8x focal reducer/field flattener

- ZWO ASI-120MM-mini guide camera - SW 9x50 finderscope

- 2 inch mounted Optolong L-eNhance

 

Acquisition:

- Sharpcap polar alignment, ST4 autoguiding with PHD2

- Manual acquisition using intervalometer

- Lights – 15 x 180s (45 minutes)

- Darks – 25

- Bias – 30

- Flats - 30

 

Processing:

- Stacked and calibrated in APP using HA and OIII extract algorithms

- Monochrome images combined in PS CS6 (HOO Palette)

- Crop to area of interest

- Levels/curve stretch

- Unstretched core blended carefully onto stretched image so that it was less blown-out

- Contrast enhancement and denoise

- Slight desaturation of brightest stars (they appear too blue with the L-eNhance filter)

 

[Rustang]

You have some lovely detail there, the cores fairly well handled. To me though the colors a bit to much on the red/pink front, its making it a little difficult to look at! but that's my own personal view. There's some noise/texture that's really present, might be slightly over stretched!? Cracking though mate, you must be pleased, Orion's always a winner. 👍

Edited September 26, 2020 by Rustang

[ollypenrice]

It's good, but I'll make constructive comments.

To control the core on M42 you really will need short subs. It's one of very few objects for which this is essential. The whole Trapezium region is saturated here.

For me there is green where there ought to be blue. What's showing as green here is not OIII emission but reflection nebulosity. Your OSC camera without the filter would have shown this. What is your filter bringing to the table?

Olly

[R1k]

1 hour ago, Rustang said:

You have some lovely detail there, the cores fairly well handled. To me though the colors a bit to much on the red/pink front, its making it a little difficult to look at! but that's my own personal view. There's some noise/texture that's really present, might be slightly over stretched!? Cracking though mate, you must be pleased, Orion's always a winner. 👍

 

23 minutes ago, ollypenrice said:

It's good, but I'll make constructive comments.

To control the core on M42 you really will need short subs. It's one of very few objects for which this is essential. The whole Trapezium region is saturated here.

For me there is green where there ought to be blue. What's showing as green here is not OIII emission but reflection nebulosity. Your OSC camera without the filter would have shown this. What is your filter bringing to the table?

Olly

thanks both for the very helpful comments, I agree it is overstretched and probably a bit oversaturated.

 

Olly - Many thanks again, this type of feedback is exactly what I am after. how short should the subs be for the core? We talking 30s and less? As for the filter, I’m fairly new to the hobby, so assumed that any object with emission nebulosity would benefit from a NB filter. I will have a bash without a filter and see how it compares. 

 

thanks again both!

[Rustang]

Pretty sure I've read this somewhere, and it's something I may try myself but I think it might be worth combining two sets of subs. Take a set of shorter subs to control the core then some longer subs for fainter details then blend the two stacked images later in post. 

Edited September 26, 2020 by Rustang

[ollypenrice]

11 hours ago, R1k said:

 

thanks both for the very helpful comments, I agree it is overstretched and probably a bit oversaturated.

 

Olly - Many thanks again, this type of feedback is exactly what I am after. how short should the subs be for the core? We talking 30s and less? As for the filter, I’m fairly new to the hobby, so assumed that any object with emission nebulosity would benefit from a NB filter. I will have a bash without a filter and see how it compares. 

 

thanks again both!

 

11 hours ago, Rustang said:

Pretty sure I've read this somewhere, and it's something I may try myself but I think it might be worth combining two sets of subs. Take a set of shorter subs to control the core then some longer subs for fainter details then blend the two stacked images later in post. 

How long your short subs should be is very kit-dependent. For my own M42 efforts ( https://www.astrobin.com/380941/?nc=user and https://www.astrobin.com/321869/?image_list_page=2&nc=&nce= )  I used 11 seconds for the Trapezium stars and 50 seconds for the Trapezium region, then 15 minutes for the outlying parts. That's using cooled monochrome CCD.

When assessing a sub length look at what is saturated (burned to white) in the linear sub. Anything saturated is saturated for good. You can do nothing with it.

For how to blend different exposure lengths you cannot beat this method: https://www.astropix.com/html/j_digit/laymask.html

Regarding the filter (which I've never used) my understanding is this: it will block wavelengths other than Ha, OIII and H Beta. In order, those wavelengths lie roughly in the red, the green and the blue. So will they approximate to RGB? No.  Although H Beta is blue, it is emitted by much the same gasses as are shining in Ha so it will only add rather faint blue signal to what is already there in the Ha. The OIII line lies right on the blue-green border so that, too, will pass a small amount of the longer wavelength blue. But neither the H Beta nor the OIII will pass the bulk of the signal from blue reflection nebulosity. Quite a lot of the Running Man feature is made up of broadband blue, so the filter is stopping it.

I'd try the filter thus: Shoot and process a full spectrum RGB without it. Shoot and process a version with the filter, such as you already have. Apply the NB version over the full spectrum one in Photoshop's Blend Mode Lighten. That way the NB image will only brighten those parts where it has allowed you to find more signal. Where the RGB image has more blue, it should be unaffected by the top layer. (Warning, I haven't tried this. Normally I split my RGB channels and add Ha to red and OIII to green and blue in blend mode lighten. You might have to split channels in both your RGB and NB images and do it as I do but it might work done 'all in one.' I don't know.)

Olly

 

[R1k]

54 minutes ago, ollypenrice said:

 

How long your short subs should be is very kit-dependent. For my own M42 efforts ( https://www.astrobin.com/380941/?nc=user and https://www.astrobin.com/321869/?image_list_page=2&nc=&nce= )  I used 11 seconds for the Trapezium stars and 50 seconds for the Trapezium region, then 15 minutes for the outlying parts. That's using cooled monochrome CCD.

When assessing a sub length look at what is saturated (burned to white) in the linear sub. Anything saturated is saturated for good. You can do nothing with it.

For how to blend different exposure lengths you cannot beat this method: https://www.astropix.com/html/j_digit/laymask.html

Regarding the filter (which I've never used) my understanding is this: it will block wavelengths other than Ha, OIII and H Beta. In order, those wavelengths lie roughly in the red, the green and the blue. So will they approximate to RGB? No.  Although H Beta is blue, it is emitted by much the same gasses as are shining in Ha so it will only add rather faint blue signal to what is already there in the Ha. The OIII line lies right on the blue-green border so that, too, will pass a small amount of the longer wavelength blue. But neither the H Beta nor the OIII will pass the bulk of the signal from blue reflection nebulosity. Quite a lot of the Running Man feature is made up of broadband blue, so the filter is stopping it.

I'd try the filter thus: Shoot and process a full spectrum RGB without it. Shoot and process a version with the filter, such as you already have. Apply the NB version over the full spectrum one in Photoshop's Blend Mode Lighten. That way the NB image will only brighten those parts where it has allowed you to find more signal. Where the RGB image has more blue, it should be unaffected by the top layer. (Warning, I haven't tried this. Normally I split my RGB channels and add Ha to red and OIII to green and blue in blend mode lighten. You might have to split channels in both your RGB and NB images and do it as I do but it might work done 'all in one.' I don't know.)

Olly

 

Thanks for this Olly, totally makes sense. I will try this entire technique (RGB with various sub lengths, blended and the NB layer on top) in the coming months when I get to have a bit more time on the nebula. Very much appreciate you making the effort to explain this in great detail, have certainly learned a few things that I’ll be able to move to other projects/targets too.

 

By the way, your M42 on Astrobin has totally blown my socks off, wow! 🤯