Is SII worth the bother!

[narrowbandpaul]

i found the same thing with my O[iII] bubble...

not much there, just the bit nearest the wolf rayet...sulphur a touch better, IMHO

give it 10 of those...and youre well on the way to a good image...just add some Ha to serve.

I will visit again with my friends new astrograph...

[MartinB]

The reason you should stick with the same sub frame time is to balance the star colour better. The star signal for a "white" G2V star should be pretty similar through all 3 filters. If you mix the sub exposure length you will have varying star saturation between the filters.

As Paul says, you should go for as long exposures as you can manage or until a point where the background sky glow stars to become a factor.

[narrowbandpaul]

the one key point is that you need to get as many signal electrons in the pixels as possible.

[narrowbandpaul]

the files are going on now to UK astronomers...narrowbandpaul

[narrowbandpaul]

files up I think

UK astronomers tried to make it as hard as possible...but I won

[MartinB]

Brill, thanks Paul. I'm going to experiment!

[MartinB]

I've had a look at different combinations of the excellent data provided by Paul. I have been interested in seeing how much the SII contributes to a typical narrow band image and whether creating synthetic channel from just OIII and Ha has the potential for providing almost as good a result. I found that assigning OIII to red and blue channels (or doing the same with SII for the that matter) was unsatifactory. However, using a synthetic green channel taken from Ha in red and OIII in blue gives some nice nuances of colour without much apparent loss of detail despite no contribution from SII. To my eye the bicolour lacks the drama of the hubble palate but is a somewhat more natural looking image. On balance I think I prefer the hubble style image, I like the yellow contrasting against the green, things stand out that bit more compared with yellow against salmony orange.

However if the time had been spent capturing more OIII and Ha rather than the SII the s/n would have been that much better in the bicolour version. So for me the jury is still out.

I would be very interested in hearing what other people think. A lot of this is very subjective aesthetic preference. Lets not kid ourselves it's science!!

(click to enlarge)

(click to enlarge)

[Whippy]

As you say Martin, it's purely down to what you prefer. Someone on here did the Bubble in the same pallette as the bottom effort and I thought it looked great, other didn't so I guess it's the old 'beauty is in the eye of the beholder' argument. I've been looking at expanding my narrowband filters and whilst OIII is a bit of a no brainer, SII looks like it's more aggro than it's worth even with a fast scope. Certainly with my relatively limited time I have on clear nights, it wouldn't be worth it.

Tony..

[narrowbandpaul]

my personal preference is to not use a synthetic green channel, but i am biased toward the science

why are we so quick to rule out S[iI]. I'd rather do away with O[iII]

each to his own I guess

[MartinB]

Yes, you could do the same with SII in preference to OIII although I thought there was quite a bit more OIII than SII in the data set. It was great data to work with Paul. The signal strength of the Ha channel was fantastic, excellent resolution as well thanks to great optics and tracking

[GordonH]

Hi all

Regarding the argument about whether to bother with SII or not is more difficult than it sounds. There are a plethora of nebula, SNR and planetaries out there that are crying out for emission line imaging to show their hidden detail in all their beauty, the problem is they don't all have the same quantities of Ha, OIII and SII in fact some are virtually bereft of one if not more of the emission lines. As Martin quite rightly says using Ha and OIII and creating a synthetic channel gives a more natural appearance but lacks the drama of a HST palette. To totally ignore either the OIII or SII because they are "too much trouble" could mean the difference between a very good image and a truly spectacular image, so from this point of view I think it is better to have all of them if you are interested in emission line imaging. Now this brings me to something that I have started to do to help give me an idea of what I might be in for when deciding which target to choose for emission line imaging, first of all I do a check on the internet to get some idea as to the ratios and amount of the emission lines in a particular subject and then I check on a few sites of some of the more experienced NB imagers to get some idea as to the best exposure times and number of subframes per filter. This then gives a rough idea as to whether the subject can be imaged in one night, several nights or whether it is a long term project.

Personally I do feel that OIII and SII are worth the bother but there are a whole lot of other issues such as speed of scope, QE for different emission lines for the camera, how much time you are willing to devote, processing skills, etc. that come into the equation as well

I think this is a great thread Martin that has provoked a lot of interesting discussion as well as useful information in the replies

Best wishes

Gordon

[narrowbandpaul]

likewise gordon...I check out rdc's efforts before deciding how long, how many subs..for example crescent neb has Ha, and O[iII] in a good abundance but S[iI] is non existant...so here I would spend more time getting at S[iI]

very good reply gordon, its not as simple as saying, S[iI] is too much effort

Best Wishes

Paul

[barkis]

So is there a catalogue of objects that are known to be worthwhile doing NB imaging on, or is the list unofficial, and only known about by trial and error so to speak.

Ron.

[narrowbandpaul]

any object with compression (shock) or a central star/star cluster should be a good NB target, but there is trial and error

[RichieJarvis]

Yes - thanks to all the experts who've posted - this has been a most interesting discussion. I think that in time I will purchase an S[iI] filter, but for now, I will stick with just Ha and O[iII] until i've got the hang of it

Sounds to me like the crescent will be a good target for me to practice on. The Bubble doesn't seem to have much O[iII] emitting from what I can tell - certain with respect to the Ha emission that that particular nebula!

Thanks all,

Richie

[narrowbandpaul]

no worries richie...

crescent ought to be a good target...better get out early though.

bubble seems largely devoid, apart from the area immediately surrounding the bubble part itself.

would look good though at high res....

[MartinB]

I'm currently playing with layer sets, clipping masks and adjustment layers to see how close I can get to a hubble palate using 2 colour channels. I may be gone some time!

[Whippy]

So is there a catalogue of objects that are known to be worthwhile doing NB imaging on, or is the list unofficial, and only known about by trial and error so to speak.

Ron.

Ron, there's the sharpless catalogue which lists emission nebulae otherwise I tend to have a look at what constellations are in the right part of the sky for me and use the Deep Sky Browser to seatch out potential targets.

Tony..