Can I use Ha as luminance ?

[Daniel-K]

Say I imaged  a said object through a HA filter could I use that data as luminance instead of capturing L data instead? 

[Oddsocks]

Yes, if the object is an emission nebula then Ha can replace the luminance channel, if the object contains a broad range of emitted wavelengths then not really since you will be missing most of transmitted light from the object.

[Daniel-K]

Thanks oddsocks that makes sense.

[ollypenrice]

Personally I try to avoid using Ha as luminance because it imposes the brightness patterns of red onto the entire image, including all those parts which are not red. In particular the effect on star colour is detrimental. In the case of targets which are Ha dominated, and there is no blue reflection nebulosity to worry about, then I will use Ha as luminance but only up to an opacity of about 15%.

I feel the best way to use your Ha layer is as an addition to red in blend mode lighten. If you do this the Ha brightens the red where Ha is brighter than red and leaves it alone elsewhere. It has almost no effect on star colour either. 

We used to see lots of 'Ha as full on luminance' images and they tended to be mainly pink with blue star halos.

Olly

Edit: BTW Ha can be applied to red in blend mode lighten to any  image, even one with very little Ha. Galaxies come to mind.

[swag72]

I always use Ha as luminance in narrowband work, but on the odd occassion when I do LRGB then I would do as Olly says and put the ha into the red channel and gather proper luminance data for the L channel

 

[ollypenrice]

1 minute ago, swag72 said:

I always use Ha as luminance in narrowband work, but on the odd occassion when I do LRGB then I would do as Olly says and put the ha into the red channel and gather proper luminance data for the L channel

 

Good point. I was talking only about using Ha as luminance for broadband, not narrowband, where the whole situation is different.

Olly

[Daniel-K]

my targets will mostly be galaxies as I've bought a RC6 and will be imaging at F9 to keep the FL.  

I may do some up close details inside nebulae at some point that was why I was asking. 

cause my chip is a 414ex if image a part of the wall in the North American nebula would using HA as luminance  be okay ?

[ollypenrice]

I prefer the method I describe. This is my N America (mosaic) using that method - so Ha mostly blended to red in blend mode Lighten and very sparingly applied as just a hint in luminance.

In galaxies you have to apply Ha to red or you'll kill the rest of the target. Your Ha may need to be given a big stretch while it's sitting on top of the red channel in blend mode lighten before it does anything you can see. Stretch away till it does appear then flatten Ha onto red and recombine the channels.

Olly

 

[Daniel-K]

Cheers Olly.  

For galaxies am I best keeping all the exposure lengths for each channel the same? 

[ollypenrice]

Just now, Daniel-K said:

Cheers Olly.  

For galaxies am I best keeping all the exposure lengths for each channel the same? 

It makes processing easier if you have equal weightings in all channels. However, if you're chasing faint tidal tails or outer glows then you might want to get a monster dose of luminance. If you do this you can't just apply a heavy lum straight onto a lighter RGB or it will wash out the colour. Briefly, the way to apply heavy lum to light RGB is to apply it a bit at a time. Boost the saturation and add a bit more. Repaeat till you have the full luminance applied. For starters I'd advise you just to shoot equal sets of LRG and B.

Olly

[Daniel-K]

2 hours ago, ollypenrice said:

It makes processing easier if you have equal weightings in all channels. However, if you're chasing faint tidal tails or outer glows then you might want to get a monster dose of luminance. If you do this you can't just apply a heavy lum straight onto a lighter RGB or it will wash out the colour. Briefly, the way to apply heavy lum to light RGB is to apply it a bit at a time. Boost the saturation and add a bit more. Repaeat till you have the full luminance applied. For starters I'd advise you just to shoot equal sets of LRG and B.

Olly

do you know of any websites that explains adding RGB to L ?

[Scott]

8 minutes ago, Daniel-K said:

do you know of any websites that explains adding RGB to L ?

I'll go over it with you at sgl11 if you want

[ollypenrice]

I don't know of a website but the process is explained in the book Lessons From The Masters edited by Rob Gendler. I was lucky enough to get a copy because I'm one of the book reviewers for Astronomy Now. It really is a helpful book with plenty of useful techniques which have become part of my workflow.

Olly

[opticalpath]

15 hours ago, Daniel-K said:

do you know of any websites that explains adding RGB to L ?

Robert Gendler has a series of good articles on his website covering much of this, including:

- basic process of combining L with RGB  http://www.robgendlerastropics.com/LRGB.html
- the more advance 'multiple luminance layering' method (adding the luminace in stages as Olly described)  http://www.robgendlerastropics.com/LLRGB.html
- adding in Ha to enhance images of nebulae.  http://www.robgendlerastropics.com/HARGB.html

Adrian

 

 

 

[ollypenrice]

8 hours ago, opticalpath said:

Robert Gendler has a series of good articles on his website covering much of this, including:

- basic process of combining L with RGB  http://www.robgendlerastropics.com/LRGB.html
- the more advance 'multiple luminance layering' method (adding the luminace in stages as Olly described)  http://www.robgendlerastropics.com/LLRGB.html
- adding in Ha to enhance images of nebulae.  http://www.robgendlerastropics.com/HARGB.html

Adrian

 

 

 

Great links. 

Olly

[betelgeuse91]

On 03/02/2016 at 11:20, ollypenrice said:

I prefer the method I describe. This is my N America (mosaic) using that method - so Ha mostly blended to red in blend mode Lighten and very sparingly applied as just a hint in luminance.

In galaxies you have to apply Ha to red or you'll kill the rest of the target. Your Ha may need to be given a big stretch while it's sitting on top of the red channel in blend mode lighten before it does anything you can see. Stretch away till it does appear then flatten Ha onto red and recombine the channels.

Olly

 

1

This is one of the most beautiful NGC7000 I have seen! Thanks for the inspiration, I am convinced to try your method for HaRGB.