Narrowband filters Question; what's what??

[davedownsouth]

So, I have got a set of Baader Narrow band filters; the ones FLO sell (Ha(7nm), OIII(8.5), SII(8.0) & Hb(8.5)).  I have used the Ha one quite a bit (works well when the moon is out), but the others hardly at all and I have never touched the Hb one.  So, I want to try using the other filters over the next two clear nights , with the Western Veil Nebula as my target (already got Ha).  So, should I go for all of the other three filters, and if I do, how do I combine them?  I.e., what is red, what is green, what is blue, what would the fourth colour be if I used all four Narrowband filters .  Hope someone has got an answer.........

[steppenwolf]

For the Veil, I'd be tempted to just collect Ha and OIII and map Ha to Red with the OIII mapped to both Green and Blue to produce a bi-colour image - you'll be surprised at how well this works to produce realistic colours. The OIII is right on the cusp between Green and Blue so can be used for both channels.

The Hb filter is a controversial one but I have found it useful for certain objects and the Rosette Nebula (but not this time of year!) is a good candidate for its use.

You could, of course have a go at the Veil in the Hubble palette mapping SII to red, Ha to green and OIII to blue. This will give you a very green image as the Veil is rich in Ha but you can manipulate the colours using the 'Selective Colour' tool in PhotoShop to generate a palette known as 'gold and turquoise' which gives a very pleasant interpretation.

Here are a couple of examples of the Veil in bi-colour with different interpretations to give you an idea of what to expect:-

[davedownsouth]

Thanks a lot Steve, really useful post and I will definitely go for OIII tonight . 

[steppenwolf]

Excellent, take plenty of OIII subframes to extract as much detail as possible to try and match the relatively high intensity of the Ha. That nearly full Moon (a blue Moon last night!) will be fun to contend with but it can be done with the filters that you have.

[davedownsouth]

Been up and running with the OIII for 20 minutes now, but the moon is so bright I can hardly see any stars, so not really expecting anything great .  Will leave it running till 1:15 and then pack up just before it does the meridian flip.  

[Uranium235]

Try to avoid shooting OIII when then Moon is about or your target is low (wait for it to rise a bit) - otherwise you will have gradients galore and its going to be hard to process.

[davedownsouth]

Try to avoid shooting OIII when then Moon is about or your target is low (wait for it to rise a bit) - otherwise you will have gradients galore and its going to be hard to process.

I took 20 x 6 minute shots in OIII (binned 2x2) on with my Atik One 6 attached to my 80/480 Altair Wave scope.  I processed this in PI and added it to my Ha 20 x 5 minute shots (binned 2x2) as describe by Steve; used Ha as Red and OIII as Green and Blue (never would have thought that doing this was possible ).  Processing finished in PI.  Considering the moon was very bright and my tracking last night was not the best I have seen, I was very please with the results .

[Scott]

well well, I am really surprised and impressed with this concidering the moon last night. And I've never binned ha or oiii before either. So much to learn oh learned one .

Thanks for sharing this Dave 

[davedownsouth]

 I've never binned ha or oiii before either. 

I have no idea if this is the right thing to do or not.  I am just treating them like RGB filters which need longer exposures.  Is this the wrong way to think of them 

I was also assuming that OIII and SII filters work better in moonlight like the Ha filter does?

[Scott]

I have no idea if this is the right thing to do or not.  I am just treating them like RGB filters which need longer exposures.  Is this the wrong way to think of them 

I was also assuming that OIII and SII filters work better in moonlight like the Ha filter does?

I've no idea mate but looking at your image, it certainly seems to have worked

[Uranium235]

Looks like you might have gotten away with it, maybe because the FOV is small(ish), the target was high, and the Moon fairly low. Im surprised you binned the OIII since it carries quite a lot of structure separate from the Ha (on that target anyway!).

[davedownsouth]

I binned mainly because I only really had a two hour window (11 - 1am), and as I wanted ~20 shots, this means 6 minutes max and at 1x1 binning I thought would not give enough.  Still not completely sure about the binning area of imaging, but I tend to alway do colours binned 2x2 and save the 1x1 for Luminance; which I might still go for on this target once the moon has died down a bit next weekend .

EDIT.  To me, if I had not binned, the picture would have been twice the size, but would have taken half as long again to take, is this statement kind of correct or am I missing something

[ollypenrice]

I binned mainly because I only really had a two hour window (11 - 1am), and as I wanted ~20 shots, this means 6 minutes max and at 1x1 binning I thought would not give enough.  Still not completely sure about the binning area of imaging, but I tend to alway do colours binned 2x2 and save the 1x1 for Luminance; which I might still go for on this target once the moon has died down a bit next weekend .

EDIT.  To me, if I had not binned, the picture would have been twice the size, but would have taken half as long again to take, is this statement kind of correct or am I missing something

Yes, pretty correct. However, the difference between multiple channel NB imaging and LRGB is that the colour layers in LRGB (that's to say the RGB) don't carry the detail. That comes from the L. However in multi channel NB imaging all the channels carry fine structural detail if the object is emitting in all three. So binning will compromise that detail badly, and there will be no equivalent of an L channel to replace that lost detail. By all means bin to produce a smaller (less resolved) NB image but remember that you should get the same result by not binning and then downsizing the unbinned image in software. If you do that you can go back another time and collect more unbinned data.

Nutshell, I wouldn't bin narrowband.

H beta is an oddball because it's blue, when Ha is red, but it traces the same gasses most of the time, only with a fraction of the signal. You can cheat by giving a whiff of Ha to the blue channel as a substitute H beta.

I've never used SII.

Olly

[davedownsouth]

Yes, pretty correct. However, the difference between multiple channel NB imaging and LRGB is that the colour layers in LRGB (that's to say the RGB) don't carry the detail. That comes from the L. However in multi channel NB imaging all the channels carry fine structural detail if the object is emitting in all three. So binning will compromise that detail badly, and there will be no equivalent of an L channel to replace that lost detail. By all means bin to produce a smaller (less resolved) NB image but remember that you should get the same result by not binning and then downsizing the unbinned image in software. If you do that you can go back another time and collect more unbinned data.

Nutshell, I wouldn't bin narrowband.

H beta is an oddball because it's blue, when Ha is red, but it traces the same gasses most of the time, only with a fraction of the signal. You can cheat by giving a whiff of Ha to the blue channel as a substitute H beta.

I've never used SII.

Olly

Okay, that is the piece of information I was missing .