Teasing out that hydrogen redness

[Mark2022]

Hi Guys,

Processing drives me nuts! I have zero idea what I'm doing, how to properly use photo processing tools, masks, curves, channels etc. I've  watched a ton of YT videos related to it and yet still, when it comes to my own pics (of which, I only have a couple since I am very new to the whole thing since giving up Astronomy in my 20s, getting married and, at that time, there was no such equipment and processing capability there is now - I'm now 60) I spend hours and hours just playing with all the processing elements with no idea what comes first, what to do next and how to tease out the nebula. In fact, I just took exposures last night of Deneb, Sadr and their general region, hoping to get the North America nebula and Sadr region gas and I achieved it (to an extent) but I tried to improve on my processing today and couldn't remember the steps I took the night before to bring out all that red. It's not a great pic but it's the best I've achieved thus far.

As a background, I used a standard, unmodified Nikon D5500 with a Samyang 85mm F1.4 lens (stopped down to F4) on a StarAdventurer 2i with 30, 90 second subs and 5 darks. No filters. I live in a bortle 4 but with street lights around (although they didn't directly disturb things).

I appreciate I've over-processed the image and that's part of my issue - to tease out the nebula without over-processing - plus I went too far in star reduction. I used Affinity Photo for stacking and processing - no other software used.

I always seem to have an image that ends up too blue and it is a real struggle to get the reds - again, how I managed this in this photo, I cannot even repeat myself! There was zero nebula to be seen in the subs and even when stacked.

So my question is (to anyone who is competent with processing and especially if you've used Affinity Photo but even Photoshop): What are the prime steps to teasing out the emission nebulae in stacked photos? And how to do it without the image ending up looking over-processed, too blue and reducing that purple/blue 'glare'?

[WolfieGlos]

Three. things jump out. Firstly, you mention lights and darks, did you take any flats and bias frames?

Secondly, the unmodified camera will be a problem.

The red in nebulae ( typically known as emission nebula) is in the Hydrogen Alpha wavelength of light, which is beyond the visible spectrum of light and which our DSLR cameras are designed to block out. Otherwise photos would have a red cast to them.

Saying that, they don’t block all of the Ha wavelength, typically with Canons circa 80% of Ha is blocked by a filter. By removing that filter it allows around 95% of that light through to the sensor. You can either get your camera modded or buy a second camera that is modded, which is what I did from astronomiser (or elsewhere). His website gives a good explanation: http://www.astronomiser.co.uk/intro.htm http://www.astronomiser.co.uk/filters.htm .

That’s not to say that unmodded is useless, it will work well for galaxies and reflection nebula (typically blue, I.e. The Pleiades). Unmodded will also work for brighter emission nebula but it will require a lot more exposure time than a modded camera. 

Third, total exposure time. 45 minutes isn’t a lot. Generally images have hours of subs to generate that final image, getting more signal and less noise, and allowing fainter details to come through.

Heres an example of a work in progress I’m currently imaging. It’s 15 x 180 frames (45mins) , iso 800 in bortle 4 taken at f5.6. Canon 800d, modded with an lenhance filter to isolate specific wavelengths of light. It’s by no means finished needing more time for the outer shell, but this shows the difference a modded camera will make with the same amount of integration time. Stacked and processed in Siril and gimp. 

[Elp]

OSC narrowband filters also work like magic for ha and o3 emission nebulae, especially in light polluted environments.

Edited June 21, 2023 by Elp

[Mark2022]

9 hours ago, WolfieGlos said:

Three. things jump out. Firstly, you mention lights and darks, did you take any flats and bias frames?

Secondly, the unmodified camera will be a problem.

The red in nebulae ( typically known as emission nebula) is in the Hydrogen Alpha wavelength of light, which is beyond the visible spectrum of light and which our DSLR cameras are designed to block out. Otherwise photos would have a red cast to them.

Saying that, they don’t block all of the Ha wavelength, typically with Canons circa 80% of Ha is blocked by a filter. By removing that filter it allows around 95% of that light through to the sensor. You can either get your camera modded or buy a second camera that is modded, which is what I did from astronomiser (or elsewhere). His website gives a good explanation: http://www.astronomiser.co.uk/intro.htm http://www.astronomiser.co.uk/filters.htm .

That’s not to say that unmodded is useless, it will work well for galaxies and reflection nebula (typically blue, I.e. The Pleiades). Unmodded will also work for brighter emission nebula but it will require a lot more exposure time than a modded camera. 

Third, total exposure time. 45 minutes isn’t a lot. Generally images have hours of subs to generate that final image, getting more signal and less noise, and allowing fainter details to come through.

Heres an example of a work in progress I’m currently imaging. It’s 15 x 180 frames (45mins) , iso 800 in bortle 4 taken at f5.6. Canon 800d, modded with an lenhance filter to isolate specific wavelengths of light. It’s by no means finished needing more time for the outer shell, but this shows the difference a modded camera will make with the same amount of integration time. Stacked and processed in Siril and gimp. 

Hi Chris,

Thanks for the reply. No bias or flats taken.

I'm not interested in going down the astro mod route. I'm not looking for perfection and the amount of Ha the camera captured in 45 mins satisfies me. It's the processing aspect which interests me (although I take onboard that perhaps the lack of flats and biases haven't helped that blue gradient). My main issue is I don't know how I actually teased out the Ha red that I did and I would like it to be repeatable.

[Mark2022]

8 hours ago, Elp said:

OSC narrowband filters also work like magic for ha and o3 emission nebulae, especially in light polluted environments.

Hi Elp - I think "Yes and probably increase the needed exposure by a factor of at least 2"?

[vlaiv]

11 hours ago, Mark2022 said:

So my question is (to anyone who is competent with processing and especially if you've used Affinity Photo but even Photoshop): What are the prime steps to teasing out the emission nebulae in stacked photos? And how to do it without the image ending up looking over-processed, too blue and reducing that purple/blue 'glare'?

Maybe post raw unprocessed stack to see what other people can make of it?

I'm guessing that you'll be surprised by results, but that also means that various pieces of software will be used - not necessarily what you have available.

In any case - there is a learning curve for processing, and seeing what is possible with your data will give you incentive to hone your skills and maybe even try different approaches.

[Elp]

53 minutes ago, Mark2022 said:

Hi Elp - I think "Yes and probably increase the needed exposure by a factor of at least 2"?

Not really. This is a different setup as aperture helps with speed of signal capture but this is an example of 30 minutes (see post 16th June 2023):

https://stargazerslounge.com/topic/401548-i-feel-the-need-the-need-for-speed-hyperstar-rasa-any-fast-f-ratio-telescope-imaging-thread/?do=findComment&comment=438

 

Edited June 21, 2023 by Elp

[AstroMuni]

On 21/06/2023 at 00:15, Mark2022 said:

I appreciate I've over-processed the image and that's part of my issue - to tease out the nebula without over-processing

In your image there is a gradient, hence why some parts are looking bluer than others. I use Siril in which you can remove gradients as the first step and then you can slowly stretch the image to bring out the nebula. It also integrates with Starnet so you can stretch stars and nebula independently. I am sure Affinity photo also allows most of these.

[Mark2022]

On 04/07/2023 at 16:01, AstroMuni said:

In your image there is a gradient, hence why some parts are looking bluer than others. I use Siril in which you can remove gradients as the first step and then you can slowly stretch the image to bring out the nebula. It also integrates with Starnet so you can stretch stars and nebula independently. I am sure Affinity photo also allows most of these.

Hi Astromuni, Yes, I've since used Siril and I guess you mean the background extraction for the gradient?Yes, it's good though I note you need to experiment with it and it doesn't always get it 100% right. Also using Starnet now so yes, again, that is a fantastic tool. Thanks.

[windjammer]

I recommend GraXpert as a vg gradient removal tool - its a free download, runs as a standalone program.

Simon