33 replies to this topic

[Surfer4329]

This is my first season doing mono imaging during galaxy season.

 

What is preferable for collecting luminance data for your L channel; Ha data or using a luminance filter like an Optolong L-Pro? Or is HaLRGB the ultimate way to image galaxies?

 

I’m attaching a photo I took a couple weeks ago and used Ha data in my luminance channel. I’m happy with the outcome, but wondering if maybe I’m missing something by not collecting data through a luminance filter.

Attached Thumbnails

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[sharkmelley]

If Ha is your luminance channel then surely everywhere where Ha=0, the image should be black?

[Dan_I]

 

What is preferable for collecting luminance data for your L channel; Ha data or using a luminance filter like an Optolong L-Pro? Or is HaLRGB the ultimate way to image galaxies?

 

I’m attaching a photo I took a couple weeks ago and used Ha data in my luminance channel. I’m happy with the outcome, but wondering if maybe I’m missing something by not collecting data through a luminance filter.

The best is a true luminance filter (i.e. UV/IR cut) rather than an L-pro or any light-pollution filter.

 

The default option for imaging galaxies is LRGB. 

 

Adding Halpha  can be more or less useful depending on the target, so better to be decided on a case by case basis.

[Scott Badger]

For a galaxy, Ha as the luminance will provide far less detail than a real or synthetic luminance, or any of the color channels for that matter, but for an emission nebula it’s often the reverse. But as Dan said, adding Ha to galaxies can bring out an additional facet of the target, but it depends on the galaxy….and hard to know sometimes until you’ve spent a lot of clear sky time gathering data that might not be useful……

Cheers,
Scott

Edited by Scott Badger, 27 February 2025 - 07:16 AM.

[LPA]

Ha is useful to bring out those filaments in M82 as well as star-forming areas in the spiral arms of M81. You might try using pixelmath to combine R and Ha:

 

max(R,Ha)

 

on the non-linear masters instead of using Ha as L.

 

Larry

[f430]

Here is what you get in Ha only.

Blending this with RGB could bring out a lot of highlights.

 

Attached Thumbnails

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[Drothgeb]

I’m not a huge fan of luminance. I would display the Ha data for what it is. 
 

Edited by Drothgeb, 27 February 2025 - 06:10 PM.

[Spaceman 56]

I’m not a huge fan of luminance. 

 

Droth a question about luminance.

 

I shoot in OSC, and I don't use any filters except a UV/IR Cut.

 

in this context is my OSC sub a luminance sub ?

[Drothgeb]

Your OSC camera already has RGB filters in the bayer layer. So the UV/IR filter you’re using is in addition to those. It’s for filtering out the wavelengths (CA) that most refractors can’t properly focus. Did you know that you don’t need to use a UV/IR filter with your RC? The only case is if you’re using a reducer or flattener that has some CA.

 

You can create a synthetic luminance layer from your data. I’ve tried it, but never had any luck with it improving my image. Works much better to use a mono camera. Since you have so many scopes and mounts now, you should think about getting one. Using it to supplement your OSC camera with L or Ha data is an easy way to get started with it. The image above I shot with a 2600mc on one scope, while another scope was shooting Ha with a mono camera.
 

[Scott Badger]

Synthetic luminance's were more of a thing back when deconvolution was done manually, and usually on the luminance (shot or synthetic) only. They're not used as much now, and even shot luminance (with a mono camera) seems to be falling out of favor vs more R, G, & B time. I continue to shoot luminance because my seeing is generally poor and a lot of variability and shooting luminance when it's best improves the final image resolution. The resolution of the color channels is less critical.

 

Cheers,
Scott

[unimatrix0]

People don't want to add their Luminance, for various reasons, but mostly because they think it dilutes / fades out the color. 

 

That's because the L is applied wrong.  L always have a higher SNR than the rest of the RGB, it has more data.  As long as it's not over exposed. 

 

Having said that, the L needs to be HDR processed. It needs to have all the light data compressed without clipping or cutting the signal out. 

 

Once you do that, the LRGB image will be significantly better than just RGB or any other variation. 

https://youtu.be/Q3V...5aN_rACdyjX3iz8

[Drothgeb]

People don't want to add their Luminance, for various reasons, but mostly because they think it dilutes / fades out the color. 

 

That's because the L is applied wrong.  L always have a higher SNR than the rest of the RGB, it has more data.  As long as it's not over exposed. 

 

Having said that, the L needs to be HDR processed. It needs to have all the light data compressed without clipping or cutting the signal out. 

 

Once you do that, the LRGB image will be significantly better than just RGB or any other variation. 

https://youtu.be/Q3V...5aN_rACdyjX3iz8

Looks like the script works OK, but is still pretty limited as compared to Photoshop or Affinity. It’s hard to beat them for combining multiple images/layers. 

[Scott Badger]

Well.....more recently, Adam Block seems to be leaning more towards RGB. So long as a shot luminance is more than a third of total R, G, & B time, it can improve SNR and potentially show fainter detail, but at the expense of color information, so not necessarily a better final image.

 

Cheers,
Scott

[AstroVagabond]

I don't collect Luminance data, I just collect more R,G, & B data. After 4 year of imaging I've just started to collect Ha data this galaxy season.

[jml79]

RGB or LRGB is the best way to shoot galaxies but in many cases Ha can add some pop but you need to perform a continuum extraction between Ha and Red and then blend the Ha into Red. Luckily the SETI suite, either stand alone or in PI has some nice easy tools to make this process quick and simple. I am still an infant with LRGB and HaLRGB processing. I understand the draw to just image RGB and there is nothing wrong with that at all.

[AstroFromHome]

Galaxies in LRGB. If the galaxy is known for visible Ha regions then you compose an HaLRGB image.

I have also already seen LHaGB images. In that case not Continuum subtraction needed as you need the red for all the rest of the image too.

[auroraTDunn]

Well.....more recently, Adam Block seems to be leaning more towards RGB. So long as a shot luminance is more than a third of total R, G, & B time, it can improve SNR and potentially show fainter detail, but at the expense of color information, so not necessarily a better final image.

 

Cheers,
Scott

This is what I'm experimenting with this past year myself. Neglecting L almost completely and doing a lot more R,G,B and then creating a synthetic Lum. 

So far I like the results but dang with the skies being so crappy so often its frustrating trying to get all the time I want for each channel. 

True my color with 16hrs on each R,G,B and no lum looks so much better then 16hrs Lum and only 2-3 hours R,G,B. But again the time issue is difficult to accomplish.

 

The best cure, for me, would actually be a light switch on the moon! Seems the only really good nights I get comes with a full or near full moon which makes broadband filters a no go.

 

As for Ha, there are a few galaxies where Ha and even Oiii become a glorious thing but I use Continuum Subtraction for those and not for syn lums.

[peterc]

My last attempt was on M81, 82, NGC 3077 in LRGBHa. It seemed to work out well. Still consider myself a work in progress for processing and this was challenging. The weather certainly didn't help. I did do a HDR combo on lum and that seemed to help a good bit.

https://app.astrobin...?r=0#fullscreen

Edited by peterc, 28 February 2025 - 01:18 PM.

[Forward Scatter]

LRGBHa!

[Spaceman 56]

Your OSC camera already has RGB filters in the bayer layer. So the UV/IR filter you’re using is in addition to those. It’s for filtering out the wavelengths (CA) that most refractors can’t properly focus. Did you know that you don’t need to use a UV/IR filter with your RC? The only case is if you’re using a reducer or flattener that has some CA.

 

You can create a synthetic luminance layer from your data. I’ve tried it, but never had any luck with it improving my image. Works much better to use a mono camera. Since you have so many scopes and mounts now, you should think about getting one. Using it to supplement your OSC camera with L or Ha data is an easy way to get started with it. The image above I shot with a 2600mc on one scope, while another scope was shooting Ha with a mono camera.
 

Thanks Droth.

 

My RC10 has an Astrophysics 0.67 reducer thats made of glass, so I thought a UV/IR cut was still required ? unsure about this.

 

Just thinking about your suggestion of buying a mono camera to collect Ha Data . 

to be honest I never have a shortage of Red (Ha) in any of my images, so I have never thought that getting more red would be an improvement.

 

I also notice that many people shooting with Ha filters, or duo bands, seem to present Red dominated images, which look amateur and entirely one dimensional to me. I don't like the look at all. (I am talking about Nebula shots mostly)

 

currently i feel my OSC camera does pretty well with only the UV/IR cut. the colour balance also looks good to me.  

 

Q1. if a mono cam was used to shoot luminance only, what type of filter would be required to do this ? 

 

Q2. What would be advantages ? 

Edited by Spaceman 56, 28 February 2025 - 07:16 PM.

[jonnybravo0311]

Thanks Droth.

 

My RC10 has an Astrophysics 0.67 reducer thats made of glass, so I thought a UV/IR cut was still required ? unsure about this.

 

Just thinking about your suggestion of buying a mono camera to collect Ha Data . 

to be honest I never have a shortage of Red (Ha) in any of my images, so I have never thought that getting more red would be an improvement.

 

I also notice that many people shooting with Ha filters, or duo bands, seem to present Red dominated images, which look amateur and entirely one dimensional to me. I don't like the look at all. (I am talking about Nebula shots mostly)

 

currently i feel my OSC camera does well with only the UV/IR cut. the colour balance looks good to me.  

 

Q1. if a mono cam was used to shoot luminance only, what type of filter would be required to do this ? 

 

Q2. What would be advantages ? 

A1: Your existing UV/IR cut filter

A2: You get the entire visible spectrum of light on each pixel of the sensor, which provides a high SNR. I'm not going to get into the "is it worth it" debate

[dcbrown73]

LRGB+Ha?   (depending on the subject and the intention, as sometimes Ha isn't necessary)

 

With Mono, I wouldn't use multi band filters.  Use the filter you intend to use. (L, R, G, B, Ha, SII, or OIII)

Edited by dcbrown73, 28 February 2025 - 07:36 PM.

[Spaceman 56]

A1: Your existing UV/IR cut filter

A2: You get the entire visible spectrum of light on each pixel of the sensor, which provides a high SNR.  

Thanks JonnyBravo.  

 

1. so a UV/IR cut filter is a luminance filter when placed on a mono cam.   I always wondered about, that so thanks for the info.  

 

2. OK. so we get a higher SNR mono (black and white) image, than what we would have collected using OSC. 

 

3. from what I have read this gets superimposed on the colour data, to create a final result with more theoretical detail ?

 

is this correct ?

 

How much more detail might be expected ?

Edited by Spaceman 56, 28 February 2025 - 07:36 PM.

[Scott Badger]

Thanks JonnyBravo.  

 

1. so a UV/IR cut filter is a luminance filter when placed on a mono cam.   I always wondered about, that so thanks for the info.  

 

2. OK. so we get a higher SNR mono (black and white) image, than what we would have collected using OSC. 

 

3. from what I have read this gets superimposed on the colour data, to create a final result with more theoretical detail ?

 

is this correct ?

 

How much more detail might be expected ?

 

As has been mentioned, a 5 minute luminance equals 5 min red plus 5 min green plus 5 min blue in terms of signal, but a 1:1:1:1 ratio doesn't get you anywhere, you've only matched the luminance of the RGB. You need at least 2:1:1:1 for any appreciable gain, and some would say 3:1:1:1. So, for the same overall time budget, you can see how shooting luminance really cuts into your color data. What it gets you, in theory, is potentially more faint detail. Also, better SNR overall, but with today's noise reduction tools, I don't think that's as much of a gain. Both can be promoted further by creating a super luminance, i.e integrating all four masters together.

 

If your seeing is variable, you can also use luminance to improve resolution by shooting it during the best nights. In the final image, it's the luminance layer that carries detail/resolution, so if the color subs are shot when the seeing is poor, it doesn't really matter.

 

Cheers,

Scott

[Spaceman 56]

Thanks Scott. good answer.  

 

what I notice when I shoot Galaxies at 1484mm, and F5.9, is that its actually the colour data thats the hardest thing to bring out.

 

its very easy to get a whitish looking galaxy shot, but to get a really colourful Galaxy shot seems to be more difficult.  

 

whats your thinking on this, and how might Mono Luminance be advantageous in this context ?