Is it me, or is it [SII]? - Forums

Topic starter

Oct 24, 2023

In my last few images I have noticed that, despite a measureable signal in [SII], including in the final image actually reduces the appeal of the image.

I have tried everything I can think of

multiple attempts at different GHS/STF stretches before channel combination
NoiseXterminator before/after stretching
using Bill Blanchard's excellent narrowband normalisation process
messing around in the PixelMath expressions with the otherwise excellent Foraxx SHO palette

All to no avial. The closest I have come to is to swap the factors for Ha and [SII] in the red channel expression in the Foraxx expression, so that [OIII] rich areas favour Ha and [OIII]-poor regions favour [SII]. [Otherwise the Foraxx palette just looks too blue - but stil better the than gold/cyan of the SHO palette]. However, in all the objects I have tried to date even this palette is - in my view - almost identical or slightly inferior to the HOO Foraxx palette.

So the questions then becomes, would I be better getting 50% more time [25% in SNR] just doing Ha and [OIII]. When it comes to buying new filters, I could save $$$ on no [SII].

For a bit of fun I recently created a montage of the Tarantula, with a variety of palettes, and the standout winner for me was the Foraxx HOO.

It this just me? Are my NB combination skills just inept? Am I just too tired of the gold/cyan [HST SHO] or blue/red [Foraxx SHO] palette? Am I choosing the wrong targets?

Or it is [SII]?

Any thoughts or advice gratefully received. I suspect this topic has been debated significantly in the past, but there are a fantastic array of new tools out there which may help this issue.

Brian

Engaging

Gary Seven

Oct 24, 2023

Being an intermediate imager, here are my observations on narrowband:

1) H-a is always the dominant player. The only thing we can count on.

2) Oiii might be there. It might be usable. It often appears spatially independent of H-a.

3) Sii might be there. It might be usable. It is often spatially overlayed with H-a. You might get some interesting sharp tendrils, but often it adds little “new” detail.

Given the large H-a/Sii overlap the resulting color is a mix.

And given the H-a strength, given a good Sii signal the “effectiveness” of Sii can be preserved by taking down the saturation of H-a and making its color assignment somewhere closer to primary Red as opposed to primary Green.

Helpful Insightful Concise

Josh

Oct 25, 2023

I find the SII signal often seems concentrated at the edge of the Ha signal, kind of like an edge highlight. I usually find that it can add a new dimension to my images, and i always get excited to see a strong SII signal.

Concise

Gary Seven

Oct 25, 2023

Josh:
I find the SII signal often seems concentrated at the edge of the Ha signal, kind of like an edge highlight. I usually find that it can add a new dimension to my images, and i always get excited to see a strong SII signal.

Targets can vary greatly and sometimes it works that way. I processed my IC63 image as HSS and I realized the edge highlights you mentioned.

Brian Boyle

Topic starter

Oct 25, 2023

Thanks Josh and Gary [cool name - and I even remember seeing the original episode]. From what you say [SII] can be valuable, but may be lost on the non-AP community.

Joe Linington

Oct 25, 2023

Sii doesn't give detail but gives you an extra channel to make some colour variation with. I find it adds to the 3D effect and some of my images without much Sii can feel flat.

Michael Ring

Oct 25, 2023

Perhaps have a look at the Utah Desert Remote Observatory YouTube Channel, the way of combining channels that they do allows for interesting color experiments….
For me Sii can sometimes add depth and allows for more color, but it a real pain to get as it is usually weak and noise is usually much worse than in Ha and Oiii, partially because I take Sii around the full moon.

https://youtube.com/@utahdesertremoteobservator8328

Michael

Gary Seven

Oct 25, 2023

Michael Ring:
Perhaps have a look at the Utah Desert Remote Observatory YouTube Channel, the way of combining channels that they do allows for interesting color experiments….
For me Sii can sometimes add depth and allows for more color, but it a real pain to get as it is usually weak and noise is usually much worse than in Ha and Oiii, partially because I take Sii around the full moon.

https://youtube.com/@utahdesertremoteobservator8328

Michael

I was also shooting Sii when the moon was above the horizon. However NSG was flagging much of it for low quality.

So I have switched from shooting Sii while the moon is below the horizon. So far, virtually no NSG rejects.

For now, when the moon is above the horizon I am either shooting H-a or RGB star fields to use in narrowband imaging.