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LRGB or Narrowband ?


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Hi All,

Long time member, but don't post much.

I'm moving to a Mono CCD where I was previously using a modified DSLR.

What with the cost of the camera & filter wheel,  I'm not in a position to purchase both an LRGB and HOS set of filters at the same time, so wondered what peoples thoughts were ?

Should I just go HOS? or are LRGB more forgiving?

Processing isn't an issue - I've done some narrowband processing from a remote site, and part of my processing workflow is to split, re-align and recombine the RGB channels on my DSLR data.

I'll be using 31mm un-mounted filters, and my pockets are not deep enough to spring fort the Astrodons, so it'll be Astronomiks that I'll be using.

The filter wheel with have space aplenty for the additional filters once I get around to buying them.



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If you image in light pollution, then narrowband will be the better investment in my opinion. You could go HA first to gather some nice mono images and then add OIII at a later date to turn them into Bicolour images. The benefit of narrowband is also that you can image with the moon around. The results wont be as good as with no moon but I hardly ever get a clear sky with no moon :sad:

LRGB I haven't been able to get as good results from, it really suffers in my light pollution. as a consequence even though I have everything minus SII, don't use the LRGB set very often.

If your in dark skies then your first choice may be one of taste instead?

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Thanks Rob,

Like you, I seem to only get clear skies when the Moon is up.

LP is always an issue, so it may be that HOS is the way to go.

Intrigued by the Ha only option.... maybe just get the Astrodon Ha and save for the others, instead of getting a set of Astronomiks.......

Needs a bit more thought I guess.

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It really depends on what you want to get out of the images and how long you can wait for finished products.

I've had my CCD almost a year now and a lot of targets at the start I have only gathered HA on (as I could only afford the HA filter). Now there all coming back around again so I can add OIII to last years HA for a bicolour image and increase the amount of HA I gathered as well.

Have a look in the Deep sky imaging section for HA only images and see if they take your fancy? You could always get the cheaper filters and get the whole narrowband set at once.

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LRGB is more difficult than NB at the processing stage for various reasons. (There a rules for the colour. Nature laid them down! The stars will require a lot more input to keep them down to size. Fine structure and local contrast won't just pop out of the filter. LP will get you. And more.) But you'll need more exposure.

I wouldn't try to mix ultra narrow bandpass Astrodon data with broader bandpass data from another source. The stars in our 3 Nm Astrodon are a fraction the size of those in our broader bandpass filters. You'd have a battle to avoid dodgy stars in false colour NB images if mixing Astrodon with Baader or Astronomik. (I think. I don't do false colour NB imaging personally.)


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Thanks Olly,

I wasn't thinking of mixing the narrowband filter manufacturers, just maybe getting the  Ha filter, and then saving for the others.

Is it not a good idea to mix (for example) 6nm Ha with 12nm OIII, and 12nm SII ?

I'm afraid I don't know. Perhap^s a narrowband imager will come along. Maybe post a specific thread on this question?


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It is perfectly reasonable to mix FWHM filter widths but not the way round you've got them.

Some imagers actually prefer to use smaller FWHM width OIII and SII. The main problem encountered is that there's normally loads of Ha in the usual nebula suspects and much less OIII and SII. What tends to happen is that many imagers want a sea of blue OIII all round their Ha for instance. To do that you'd have to stretch the OIII very hard. What then happens is that the stars begin to stretch along with the signal. Starting with smaller stars gets round this to some extent. Star masks don't always work for every one.

Another way round it would be to try and reduce the stars in the OIII layer/s. This can be done in PS, PI etc. or maybe using deconvolution.

A consideration can also be given to light pollution. Smaller OIII FWHM widths will help defeat the moon and so OIII and Ha can be collected with an early or late moon. ( They say :) )

I chose to stick with one width ( 5nm )and use the processing methods, as do most people.

So - Why do Baader make wider OIII and SII than their 7nm Ha ? Not a clue.


Edit - I've just noticed you said 31 unmounted filters ( QSI or Moravian camera ? ). Astronomik do them as do Astrodon. If I was starting out again with a restricted budget, I'd buy a 5nm Ha Astrodon first and then wait until I had the cash for an OIII. 

Edited by davew
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