Narrow Band Filter question

[ian_bird]

Hi

I already have a set of 2 inch Astronomik 12nm NB filters - HaII, OIII and SiII.

I have just bought an Astrodon 3nm HaII.

I saved a small fortune buying a 31mm filter and an adapter from TS, rather than the 2 inch Astrodon.

I saved so much - I can afford to buy another two filters from Astrodon.

So what do I go for?

My first thought is 5nm HaII. Less contrast - but less pain - especially if the moon is out of the equation. Use the 3nm when the moon is around, 5nm when it's not.

(Here I should explain I am battling horrible neighbour induced light pollution, and most of the time, the moon.)

Second thought is - does having 3nm or 5nm OII or SiII really help - or are my 12nm ones OK. Is it like LRGB where Luminance gets the detail - and RGB just provides the colour?

Anyone have any thoughts?

Olly - thanks for your original advice. I didn't want to bug you personally again - hence posting this here.

Cheers

Ian

[ollypenrice]

I think the 3-5 distinction will be subtle. I also think that 12 Nm is far too broad for contrast creation and, perhaps, LP rejection - though I know nowt about that. OIII is not very moon proof whatever bandpass you go for.

Olly

[swag72]

I went for 3nm across the board - I'm glad that I did and would recommend that way to anyone.

[ian_bird]

So maybe go for the OIII?

Is it not like LRGB? Do you need your OIII to have the same contrast as your HaII?

I guess maybe so. After all - you are combining them in a way different from L and RGB.

Not sure though.

Cheers Olly.

Ian

PS - Interesting that the 3nm OIII is not moon proof. I wonder why? Green cheese reflecting in the OIII wave length?

[swag72]

With the OIII and Ha you will be able to create most pleasing bi colour images. My SII is the least used for sure. I would say that you want your OIII star sizes to match your Ha as much as possible otherwise you will end up with halos in your final processing.  

[ollypenrice]

Yup, Sara has it. It's the star sizes that need to match between filters and the tight bandpasses hold down the stars to an incredible extent. I need to resort to all kinds of Photoshop thuggery when combining an not-very-good OIII filter with Astrodon Ha. I can only get away with it in enhancing colour images. It wouldn't do at all for the kind of NB imaging that Sara does.

Olly

[ian_bird]

Thanks Sara and Olly

That makes perfect sense now you come to mention it! I had not considered star sizes.

Thanks ever so much. Really appreciate the advice.

Cheers

Ian

[PatrickGilliland]

Just to put a different view on it - if cash permits OIII and SII 3nm all the way.  Ha is a little more tricky and having both 3 & 5 nm if an option could be considered.  But note at 5nm Ha also includes a little of the NII band, this typically provides a slightly more crisp, straight from the scope the 3nm i found, and only from personal observations was a little softer than 5nm especially when the LP/moon was in play.  At first that sounds counterintuitive but thinking it through it makes sense as you are on a tighter pass, without the reinforcing NII data and the LP will kill some of the signal.  

All that said we are talking fractions here - i think given that you have 3nm already stick with it and if you want something different you can add an NII which can provide some interesting data especially on some PN's.

Paddy 

[ian_bird]

7 hours ago, PatrickGilliland said:

But note at 5nm Ha also includes a little of the NII band, this typically provides a slightly more crisp, straight from the scope the 3nm i found, and only from personal observations was a little softer than 5nm especially when the LP/moon was in play.

Hi Paddy

Thanks for the feedback. Not 100% sure I followed the bit above - but I think you are saying that 5nm can do better than 3nm when there is LP/moon about. And will produce a crisper image under those conditions due to the inclusion of NII.

Pretty sure that was the gist of it. In which case - food for thought indeed!

Maybe 3nm OIII and 5nm HaII in addition to the 3nm HaII already purchased.

Thanks again Paddy (and Olly and Sara).

Cheers

Ian

[DaveS]

I went 3nm across the board. I've also found the [NII] to be more use so far than [SII], YMMV.

[ian_bird]

Thanks Dave. I'm going to have to look into this NII a bit more. ;-)

Cheers

Ian

[DaveS]

To avoid posting it again, have a look in the DSO Imaging Showcase, where I posted an image of the Rosette in HNO, with HII mapped to red, [NII] mapped to green and [OIII] mapped to blue.

[ian_bird]

Will do Dave. Tea time beckons - but will take a look ASAP.

Cheers.

[PatrickGilliland]

1 hour ago, ian_bird said:

Hi Paddy

Thanks for the feedback. Not 100% sure I followed the bit above - but I think you are saying that 5nm can do better than 3nm when there is LP/moon about. And will produce a crisper image under those conditions due to the inclusion of NII.

Pretty sure that was the gist of it. In which case - food for thought indeed!

Maybe 3nm OIII and 5nm HaII in addition to the 3nm HaII already purchased.

Thanks again Paddy (and Olly and Sara).

Cheers

Ian

Easiest thing to do will be to have a look at the bandwidths for each channel and then add the filter pass, you will see at 5 you include a little Nii which i found under UK skies gave me better detail - trade of more noise and stars not quite so tight, yes, noise in Ha not an issue generally.  Sor me me in UK 5 is fine.  If under dark skies go 3 as less light to remove fine signal so more likely to pick up the detail still.

 

Paddy

[DaveS]

I've put these up before, but just as a comparison, here are two Rosettes from the same HII, [NII] and [OIII] data.

For the first I've combined the HII and [NII] data into the red channel, then duplicated the [OIII] into the green and blue for a bicolour.

For the second I've kept the data separate, with the HII as red, [NII] as green and [OIII] as blue

The data can also be re-mapped to an analogue of HST, with [NII} to red, replacing [SII], HII to green and [OIII] as before to blue.

So having [NII] gives you many more options, and I haven't even added the [SII] wavelengths yet (Something for next year!).

[ollypenrice]

12 hours ago, PatrickGilliland said:

Just to put a different view on it - if cash permits OIII and SII 3nm all the way.  Ha is a little more tricky and having both 3 & 5 nm if an option could be considered.  But note at 5nm Ha also includes a little of the NII band, this typically provides a slightly more crisp, straight from the scope the 3nm i found, and only from personal observations was a little softer than 5nm especially when the LP/moon was in play.  At first that sounds counterintuitive but thinking it through it makes sense as you are on a tighter pass, without the reinforcing NII data and the LP will kill some of the signal.  

All that said we are talking fractions here - i think given that you have 3nm already stick with it and if you want something different you can add an NII which can provide some interesting data especially on some PN's.

Paddy 

Paddy, I have liked every post of yours I have ever read, and so I have always liked you. Now that I understand that you have both 3 and 5 Nm Astrodons I'm not so sure. Jealousy is a terrible thing!!!!

lly

[ian_bird]

Now, now. Steady on gentlemen! ;-)

Thanks for all the very informative replies. I feel honoured!

A quick question before I gallop off down this course (OK - gallop even further). I have an Atik 4000 and an SX Filter wheel with the 2" carousel (I used to have an H18). I have bought a 31mm unmounted HaII and an adapter from TS that allows me to use it as if it was a 2". Apart - obviously - from the fact that it is not 2" - it's 31mm.

Now I remember using Olly's Atik 4000 with 1.25" filters on that M31 picture. So I am assuming that 31mm will also work.

Am I right? Or is it suck it and see? ;-)

Thanks once again for all the helpful information.

And Dave - those are stonking Rosettes. I got one down at Olly's using HaII and RGB. I never dreamed I could get a decent one in the UK, but you have inspired me to try. Thanks!

Cheers

Ian

[ollypenrice]

8 minutes ago, ian_bird said:

Now, now. Steady on gentlemen! ;-)

Thanks for all the very informative replies. I feel honoured!

A quick question before I gallop off down this course (OK - gallop even further). I have an Atik 4000 and an SX Filter wheel with the 2" carousel (I used to have an H18). I have bought a 31mm unmounted HaII and an adapter from TS that allows me to use it as if it was a 2". Apart - obviously - from the fact that it is not 2" - it's 31mm.

Now I remember using Olly's Atik 4000 with 1.25" filters on that M31 picture. So I am assuming that 31mm will also work.

Am I right? Or is it suck it and see? ;-)

Thanks once again for all the helpful information.

And Dave - those are stonking Rosettes. I got one down at Olly's using HaII and RGB. I never dreamed I could get a decent one in the UK, but you have inspired me to try. Thanks!

Cheers

Ian

1.25 is fine for the Atik 4000. Being square the chip makes the most of any light cone. (OK OK, a round chip would do better... )

Olly

[ian_bird]

LOL!

Thanks Olly.

Ian

PS - Gap in the market?

[ollypenrice]

8 minutes ago, ian_bird said:

LOL!

Thanks Olly.

Ian

PS - Gap in the market?

Well, nobody sells square eyepieces...

Olly

[ian_bird]

Good point. A bit unfair on those of us who have square pupils I always thought.

;-)

[ollypenrice]

2 minutes ago, ian_bird said:

Good point. A bit unfair on those of us who have square pupils I always thought.

;-)

Most of my pupils were far from square and, if they were, I tried to bring a little jazz into their lives...

[PatrickGilliland]

56 minutes ago, ollypenrice said:

Paddy, I have liked every post of yours I have ever read, and so I have always liked you. Now that I understand that you have both 3 and 5 Nm Astrodons I'm not so sure. Jealousy is a terrible thing!!!!

lly

Did i forget to add also have some nice 6nm Astronomiks too (other brands may be available)  

On a serious note trying to figure them out, yes wider bandpass but they seem to allow more data through quicker somehow, whilst keeping stars tight and noise low - hoping to get an image out using these and the RH200/16803 (though the 8300 goes on after that) point being there are other alternatives that are not so costly and perform very well.

Paddy

[ian_bird]

We are going to get censured by the Mods at this rate. On the grounds of appallingly bad jokes.  

[Stu]

I'm saying nothin'