LRGB or Narrowband?

[vertigo262]

I am still figuring things out. And my next step is going to be going mono

And I will need to purchase filters. The question that is going through my mind is when to use LRGB and when to use Narrowband.

From what I gathered, Narrowband takes longer, but is much better in getting data, especially with light pollution. So my first thought is to get narrowband filters.

But I'm not sure if there are times you want to use narrowband, and times you want to go LRGB. 

any info on this would be helpful

[johnrt]

The type of filters depends on the target you're shooting. Narrowband filters are for emission and planetary nebula. LRGB covers everything else, galaxy, reflection nebula, molecular dust and dark nebula, integrated flux nebula, globular and open clusters, you can even cover the emission and planetary nebula too, but without the dramatic results of narrowband.

[swag72]

I consider myself a bit of a self confessed narrowband junkie really - Well over 90% of my images are narrowband I would say. Many nebulas perform well in narrowband (but I do always search the net before I start just to make sure). John has listed the types above to give you some ideas of what will and won't work with NB filters. With NB filters you have the total versatility and creativity to be able to create any colour you like!! There's also a case that you can use them while the moon would normally prohibit LRGB imaging, but I have come to the conclusion that the claims that NB can be done during a full moon is guff. If you want good, noise free data then you are better placed sitting on the sofa!

Sadly for me at least, there is a period in the season when there are precious little by way of narrowband targets and it's coming now. Generally known as galaxy season, this can be a bare time for me as well as those with short focal length scopes. So, when this cloud clears I will be embarking on LRGB in various galaxies and other bits I find along the way.

I find the processing of such very difficult indeed - The galaxies are generally colour x and that's it! There's often some Ha located within the galaxies that you can get and boost the colours a little, but whether you decide that's worth it depends.

So in answer to your questions - What could I do without if I had to? It would probably be LRGB if I'm honest. But LRGB filters are much cheaper than NB ones, so you could get LRGB as well as an Ha filter. This would enable you to use the Ha data as luminance on targets as well as give you the opportunity to grab some great mono images...... Massively underrated in my opinion.

[vertigo262]

very helpful !! ...

[ollypenrice]

I consider myself a bit of a self confessed narrowband junkie really - Well over 90% of my images are narrowband I would say. Many nebulas perform well in narrowband (but I do always search the net before I start just to make sure). John has listed the types above to give you some ideas of what will and won't work with NB filters. With NB filters you have the total versatility and creativity to be able to create any colour you like!! There's also a case that you can use them while the moon would normally prohibit LRGB imaging, but I have come to the conclusion that the claims that NB can be done during a full moon is guff. If you want good, noise free data then you are better placed sitting on the sofa!

Sadly for me at least, there is a period in the season when there are precious little by way of narrowband targets and it's coming now. Generally known as galaxy season, this can be a bare time for me as well as those with short focal length scopes. So, when this cloud clears I will be embarking on LRGB in various galaxies and other bits I find along the way.

I find the processing of such very difficult indeed - The galaxies are generally colour x and that's it! There's often some Ha located within the galaxies that you can get and boost the colours a little, but whether you decide that's worth it depends.

So in answer to your questions - What could I do without if I had to? It would probably be LRGB if I'm honest. But LRGB filters are much cheaper than NB ones, so you could get LRGB as well as an Ha filter. This would enable you to use the Ha data as luminance on targets as well as give you the opportunity to grab some great mono images...... Massively underrated in my opinion.

I agree with everything except the red bit. I would urge you not to use Ha as luminance because luminance is red plus green plus blue and Ha is deep red, not green or blue.  I would add Ha to red, where it belongs, and add it so that it brightens red where the red is less strong than the Ha.

But, grosso modo, I agree with my dear friend Sara!    (I never said I was brave...)

NB and natural colour imaging are really quite different disciplines (or sports or games or art forms or whatever.) I think Sara's right that there are more rules in natural colour. However, in NB you can, indeed, beat light pollution and you can find structures in emission nebulae that broadband will, sadly, just turn into semi-mush. As a natural colour imager my fantasy is to find a way to defeat this! But, yes, it's a fantasy. Sob.

Olly

[swag72]

I agree with everything except the red bit. I would urge you not to use Ha as luminance because luminance is red plus green plus blue and Ha is deep red, not green or blue.  I would add Ha to red, where it belongs, and add it so that it brightens red where the red is less strong than the Ha.

I suppose that I am basing this comment on my experience thus far, where I have done virtually zero by way of LRGB imaging. To date with my NB imaging I always use the Ha as a luminance layer. I certainly never add it to the red channel - It always gets blended as some sort of HOO channel and then used as luminance as well.

That's what I LOVE about NB imaging - You can do what you like

[johnrt]

Another Ha as luminance secret imager here, but only ever when I'm putting together a 100% narrowband image.

[vertigo262]

What about filter brands? are they all comparable, or any specif ones I should be looking at?

[swag72]

Baader are decent ones for the price - The more expensive Astrodons are certainly worth it for narrowband in my opinion.

[ollypenrice]

I suppose that I am basing this comment on my experience thus far, where I have done virtually zero by way of LRGB imaging. To date with my NB imaging I always use the Ha as a luminance layer. I certainly never add it to the red channel - It always gets blended as some sort of HOO channel and then used as luminance as well.

That's what I LOVE about NB imaging - You can do what you like

That's fine because in NB the colours are arbitrary anyway, but in LRGB the L is just the other colours taken all at once and not distinguished.

Olly

[vertigo262]

what about the thickness? I noticed people using different nm sizes

[Physopto]

The nm (nano metre) refers to the central wavelength of the filter not its thickness. Each narrowband filter has a central wavelength associated with it. There is a certain spread each side of this central wavelength. Some narrow band filters say 12nm and others 6 nm. It means that the 12nm filter is 6nm each side of the central wavelength and the 6nm filter is 3nm each side of the central wavelength. This spread is measure (normally) at FWHM. FWHM is the width measured across the filter graph at  half the maximum height  of the graphed wavelength. Think of a classic bell shape. The graph resembles this shape. So half way up the bell measure the width of the bell.

Using narrowband filters makes sure that no other wavelengths of light intrude in your images.

So you can cut out interference from the moon when it is affecting the normal use of LRGB.

Derek

[Physopto]

Hi here is a link to the Astronomik website. Have a look at the frequency responses of the different filters.

http://www.astronomik.com/en/photographic-filters/h-beta-ccd-filter.html

LRGB filters are not the classic bell shapes, but if you look at the narrow band graphs you will see what I mean.

Different manufacturers have slightly different spectral responses. But all aim to do the same thing. 

Derek

[ollypenrice]

The expensive tight bandpass NB filters have three advantages. They deliver higher contrasts, defeat LP and the moon better and they hold down the stars. The small stars are much nicer to behold but sometimes you need to slew away to find one on which to focus. This can be a pain (especially with a dual rig when you have to wait twenty minutes for the other scope to finish its sub! Grrrr.)

Olly