Narrowband filters

[don4l]

Are there any NB filters apart from the usual Ha, SII and OIII that people find useful?

I'm asking because I hope to have two rigs running soon, and I will need a second set of filters.  I find the SII very disappointing.  As far as I can see it does nothing apart from add a different colour to the brighter bits of the Ha data.  The structures revealed in the SII data always appear to be present in the Ha data.  So I am left with the feeling that some clever curves applied to the Ha would provide a similar result.  On the other hand, the OIII data often reveals different structures.

 

I've seen some references to He and N(e??) filters.  Are these any good?

[Davey-T]

Some folk use N11 but IIRC it overlaps other filters so depends on the band spread of your filters maybe with 3nm HA filters the N11will catch a different bit of the spectrum.

Could be talking nonsense as memory isn't what it used to be 

Some targets have more S11 than O111 

Dave

[Demonperformer]

I have added NeIII to my stable of filters. Have a look at this.

[carastro]

I only use H, O, S and agree that often Sii reveals little data, but on occasions, it is the Oiii that reveals little and Sii reveals more, but also in some targets there is signal in all 3 filters.

Carole 

[Hallingskies]

Wouldn’t it be good if there was a list of deep sky objects, tabulated against their degree of response in (say) Ha, Sll, Olll, H beta?  Does such a thing exist?  If not, I’m sure folk on this forum could use their collective experience to help put one together - if such a thing was thought to be of use...

[Demonperformer]

Something like this, you mean?

[Hallingskies]

2 hours ago, Demonperformer said:

Something like this, you mean?

Exactly like that, but for emission nebulae rather than just planetaries.  Though I suppose much will depend on your conditions and exposure time, it would be good to know in advance if a particular target offered good options in a bandwidth other than H alpha.  

[don4l]

15 hours ago, Demonperformer said:

I have added NeIII to my stable of filters. Have a look at this.

Do you have any images taken with it yet?   How do you feel that it performs?

My current camera's QE is only about 25% at the NEiii wavelength, so I also have to take that into consideration.

My problem is that I image from a terribly light polluted area, so most RG or B data is fairly rough, and requires endless processing.

If I get a second telescope going, it will be a long focal length (2000mm)

I've just got myself a 3nm Chroma filter, and I love it!  However, I cannot possibly afford another 5 of these filters.  To make matters even worse, I've just read that it is more important to have 3nm with OIII than with Ha.  The reason being that you can also use it when the moon is about! 

So, I'm wondering if I can share the filters between the two scopes.  This isn't very practical for two reasons.  The first is simple.  I do a lot of Ha imaging, so both systems would need a Ha filter.

The second reason is that moving filters around can be quite awkward.  My RGB filters are effectively within the body of the STL6303.  You cannot change these without disassembling the system.  My OIII and SII filters are in a Trutek screwed onto the front.  Another Trutek 5 position 2" wheel with two carousels would mean that I could move things about easily, but I don't think that Trutek are still in production, and the Chroma filter is too thick to fit in it anyway.

I hope that all this makes sense!

[don4l]

13 hours ago, carastro said:

I only use H, O, S and agree that often Sii reveals little data, but on occasions, it is the Oiii that reveals little and Sii reveals more, but also in some targets there is signal in all 3 filters.

Carole 

My problem with the SII is not the strength of the signal, it is that it doesn't appear to add much to the images.  The OIII can be used to create clearly differentiated colours in an image (usually blue).  The SII data just seems to change the shade of the Ha data.

 

I've played about with different combinations HSO, SHO, HOO, HSS etc.

The HSS just creates an image with different shades of the Ha data, whereas the OIII adds distinctly coloured areas.  If I "blink" the H, S and O stacks, then the S just looks like a dimmer version of the Ha, whereas the O  data looks completely different.  I could, of course be wrong about this.  I don't have a huge amount of data to play with.

I think that I am saying that the strength of the SII always bears a direct relationship with the Ha and the OIII gives something different.  If I am going to have two sets of filters, then perhaps I could do with an SII in one set and "something else" in the other.

[Demonperformer]

PM sent.

[DaveS]

I have a [NII] Astrodon in my filter wheel, and often image in NHO rather than SHO. I'll see if I can find anything to post.

[DaveS]

OK, let's see if this will work

I also posted individual stacks.

[glowingturnip]

in my limited exposure to narrowband so far, the way I'm thinking is that Ha is pretty much everywhere in the target, OIII is heavier, tends to hang around the centre of action of the target and tends to be less defined, and SII gets battered into all the wave fronts  - so has the same overall structure as Ha without maybe the prevalence across the blank bits, but adds to the contrast, both in lum and in colour, in the areas of interest.

I too wish there was a reference of which targets are strong in which wavelength

[don4l]

6 hours ago, DaveS said:

OK, let's see if this will work

I also posted individual stacks.

 

Thanks very much for that.  I'll have a good look at those stacks when I get home.

 

 

[don4l]

Hi Dave.

Well....

I've had a little play with your data.  I completely agree with the comment that the result has a 3d effect.  I've looked closely, but I cannot see why this is!  The result was very good, but I don't understand why.

I hadn't really considered NII, it is definitely a contender.

I stated above that I couldn't see a lot of difference between the structures revealed by Ha and SII.  I was wrong about this.  I've had a look at some of my images and noticed  that some of my "blue" bits are actually magenta caused by the absence of SII.

 

[DaveS]

Hi, yes the hydrogen and nitrogen are very close, perhaps just enough to create a 3D effect. There is a slight overlap, even with 3nm filters, so I don't know well separated the two data sets are.

I may have a go at this with [SII] if I get my rig up and running in time. It might be an interesting comparison.

[Demonperformer]

On 24/11/2018 at 12:32, Hallingskies said:

Exactly like that, but for emission nebulae rather than just planetaries.  Though I suppose much will depend on your conditions and exposure time, it would be good to know in advance if a particular target offered good options in a bandwidth other than H alpha.  

I've spent some time searching, but there does not seem to be a lot of info around for emission nebulae.

Burnham quotes some figures for relative abundance of elements in M42, but I'm not sure that would equate directly to experience with particular filters - if it did, then Hα & Hβ would both equate to the hydrogen abundance and they would always be directly proportional to each other.

I wonder if it would be possible to use something like the star analyser to do a test shot of the nebula to determine where the strongest signal is. I know it is usually used on point-sources, so might not work on extended sources. I've asked the question on the spectroscopy board as I am really ignorant on the subject. My gut-feeling is that it probably requires the point source or all the points would produce their own spectrograms resulting in a messy splodge, but we'll see.

[Merlin66]

Richard Walker's excellent "Spectra Atlas has some good data.

Francois' atlas is a good reference.

http://www.astronomie-amateur.fr/Documents Spectro/SpectroscopieBasseResolution.pdf

[Demonperformer]

Just goes to prove how little I know ...