Ok maybe Narrowband is just TOO hard for me

[Notty]

Hello learned people!  Now, I knew from reading that Ha was easy compared to OIII and SII but I don't think I quite realised how hard the others were and I'm mulling over selling my Narrowband filters and sticking to vanilla RGB.  Like many of us, I don't get much time to play especially as in the last 4 sessions out over 3 months I've moved from DSLR to mono CCD, FW's, SG Pro, autofocus etc etc so in many ways I'm pleased I've captured anything, but last night I was hoping for a breakthrough... but just got another disaster.  I've got strange flat behaviour as evidenced in my cry for help in the other thread, (https://stargazerslounge.com/topic/290171-asi1600mm-narrowband-flat-strangeness/) but I'd really like to know what I should have been able to capture last night in OIII, based on my equipment and the conditions.  Target was the Soul Nebula, which was pretty low on an urban horizon, and maybe I should have taken the OIII subs before the Ha, and yes there was a bit of moon glow, but really is this what I should expect from 40x90s ASI1600MM-Cool with Baader filters?  I've only given it a very basic tweak of levels but there's not much point polishing this much more, it's pretty much ALL noise.  That's 40 stacks calibrated with Darks Flats and Bias.  Compare it to the Ha in the next pic, same stats - in fact DSS even threw 10 subs out for some reason, maybe a cloud or something, not great but at least I'm in the ballpark.  So I'd love to know anyone's opinion of maybe some fundamental problem in my imaging rig, or is this likely what you get under these conditions for this band, and I just need much, much more of it?  Thank you for any input.

OIII:

Ha:

[carastro]

Very often there isn't a lot of data in Oiii and Sii, but normally there is some in at least one of them, but it does add to the colour palette.  Sometimes it is only one small area of the target that is in Oiii or Sii, but it does really enhance the finished image.  

I live in a heavily LP location, and whilst Ha will normally work, often Oiii and Sii is rubbish and noisy and needs a dark site.  

Having said that your sub length is very short only 90 secs.  I normally do either 600secs or 300 sec binned x 2, or the very least 150 secs binned x 2 (presume you know with binning you can capture data in half the time).

Carole 

 

[Notty]

Thanks Carole, the reason for the short subs is im going with the prevailing dogma for this CMOS camera i.e. many short subs, but if you're using this camera too and take long ones maybe that's something I need to look at. The trouble is i can't see anyone else's OIII subsets to compare too so I don't know what I should be shooting  for! I reckon trying to integrate this with the Ha would pretty much destroy the rest of it!

[ollypenrice]

On large nebulae the OIII often just delivers a generalized and fairly structureless glow. And OIII is not at all moon proof, unlike Ha. You may have more fun doing bicolour Ha/OIII than going for SII as well.

Olly

[Notty]

32 minutes ago, ollypenrice said:

On large nebulae the OIII often just delivers a generalized and fairly structureless glow. And OIII is not at all moon proof, unlike Ha. You may have more fun doing bicolour Ha/OIII than going for SII as well.

Olly

Thanks Olly, that makes sense but as I've seen literally hundreds of beautiful tricolour narrowband images of this target out there, I was thinking there must be enough of each ingredient to at least capture something;  I seem to be struggling.  I suppose it would be good to blame it on the moon last night even if it was only a slither!  

[ollypenrice]

2 hours ago, Notty said:

Thanks Olly, that makes sense but as I've seen literally hundreds of beautiful tricolour narrowband images of this target out there, I was thinking there must be enough of each ingredient to at least capture something;  I seem to be struggling.  I suppose it would be good to blame it on the moon last night even if it was only a slither!  

More than a slither, I'd say. We're imaging tonight but the moon is very bright. No need for head torches.

Olly

[RichLD]

I find that I have to approach OIII in particular the same way as I approach RGB i.e. dark site no moon.

Pixinsight's ABE/DBE processes can really help to get some semblance of structure and shape to your OIII and SII stacks as well 

[swag72]

I agree about OIII and SII not being moon proof....... Also you will find that there is sometimes so little OIII and SII that you wonder why you have bothered, but when you combine them, the channels do add to the final colours. Take a look at Bill Snyders site - He often shows the separate stacks on his pages..... you can see in this link that there is negligible OIII and SII. What I can't answer is how much OIII and SII you are going to get with your CMOS at such short exposures. I know that's what the ASI1600 is all about, but perhaps even with this camera, with those filters it's just not long enough..... I really don't know, just thinking out loud here.

[carastro]

That was a good demonstration link Sara, but I agree in general with what you and Olly are saying, I find generally Oiii and Sii are not Moon proof and not LP proof in many cases, and as we have all said they are still worth doing as they add to the final image.

Carole 

 

[Notty]

Thank you everyone for the advice.  So is it fair to say, generally speaking, SII and OIII don't bring very much to the party in terms of image structure but are captured mainly for colouring?

[alexbb]

Many times they don't bring too much and they are much dimmer than the Ha, many use the Ha as the single source for the luminance for some targets, but some planetary nebulas or alike are very bright in O3 and some have a very different structure.

ie. https://apod.nasa.gov/apod/ap161027.html or http://billsnyderastrophotography.com/wp-content/uploads/2011/11/M27Ha-OIII-Sync-BiPS2-V2-4web-best_.jpg or https://apod.nasa.gov/apod/ap160610.html

[Allinthehead]

Hi Notty. I also use this camera and like any camera total integration time is what really matters. I've shot Oiii with 60 second subs but captured 5 hrs, and 6 hrs for the ha at f4.9. 1 hr is just not long enough to capture anything meaningful in Oiii and you end up stretching aggressively leading to a noisy image as above. Keep adding to that data. For a nice clean image with the 80ed at f6.5 or so you should be aiming for at least 7 hrs or so for each channel, more is better. I captured 8 with my 80ed on the soul nebula in ha with 120 second subs and still had noise.

 

This is 11 hrs total in 60 second subs at gain 399 and offset 50

 

 

6 hrs Ha

 

5 hrs Oiii

As you can see i struggled with the amp glow even with darks.

Hope this helps.

Richard.

 

 

[Ant]

A similar post to Richard above. But this is a comparison of the three main narrowband lines (Ha, O[III] and S[II]) on the Pacman nebula. 

Very strong in Ha, OIII is OK but SII is poor.

These are all 900 seconds @F7 using the Starlight H9 (cannot remember the scope).

Ant

[DaveS]

I've all but given up with [SII] as the signal is often very weak, I get much better results with [NII], but you do need stupidly expensive 3nm Astrodons for both HII and [NII] to separate them. I'm on my work computer ATM (Naughty boy!) but I have some NB images at home that may be of interest. I'll see what I can dig up tonight.

[Davey-T]

I think you need to be selective, some targets have more S11 than O111, the California Nebula for one.

Dave

As we're doing examples here's mine

HA

O111

S11

 

 

[DaveS]

I had a look at my data but they don't really add anything new to the discussion so I won't confuse things.

[Adam J]

11hours of 60min subs is exactly why I did not like the idea of this camera, how long did that take to stack and how much space on the HDD?

[Allinthehead]

On 5/17/2017 at 22:34, Adam J said:

 

11hours of 60min subs is exactly why I did not like the idea of this camera, how long did that take to stack and how much space on the HDD?

 

Hi Adam. It used about 30 gb of disc space including calibration frames, and about 2 hrs to register and stack in dss. I'm not guiding yet, so i expect to start using 3-5 minute subs for narrowband when i get that sorted. This would result in an 11hr image taking up about 10 gb and shortening the stacking times. It's not an issue for me anyway as i usually let dss do its thing while at work.

Richard.

[DaveS]

ATM I use 10 min subs with the SX694 and 5 min with the ASI. With the ASI I'm using it in max DR mode from the ASCOM set-up panel. I try to keep the histo well below clipping to allow for a Sigma Add stack in AstroArt 5