NarrowBand - Lack of OIII and SII data

[DMouse]

Hi, I am fairly new at Narrowband imaging and I am having trouble with my OIII and SII subs. The last 2 nights I have been shooting IC1396 - The Elephant Trunk Nebula in Cepheus. I pushed my subs for the HA to 10 minutes (600sec) each and the HA was looking great. So I switched to OIII, but even binning a 10min subs 2x2 there was almost  nothing there. Yes the stars are there but only the slightest hint of any OIII data. The SII was even worse.

I am wondering if I am doing something wrong or am I expecting too much from the narrowband side of things? I know this sounds silly but can you put filters in the wrong side up? Finally if its a question of really long subs and a better target, what length of subs do I realistically need and whats a good target for a good Hubble Palette shot?

I am getting fed up of monochrome Ha even though it looks great. I NEED SOME COLOR

Thanks and Clear Skies

[Nocturnal]

Hi,

you've discovered that you can't capture what isn't there, congratulations

My advise is to scour the internet for NB images you like and see if they have exposure information with them. You'll probably see that planetary nebulae are a more reliable source of non-Ha radiation. There is a reason everyone likes Ha, it's everywhere!

There are probably catalogs that show the relative flux of different frequencies. I'd google that topic.

[mschuster]

+1. I have wasted many nights trying to capture what is not there.

Check out Rogelio's narrowband cygnus APOD. Hints where to find some signal.

http://apod.nasa.gov/apod/ap121130.html

Also maybe try longer exposures? I use 40 mins always binned 2x2 at f/5. More signal, less resolution IMO helps.

Mike

[Nocturnal]

More signal, less resolution IMO helps.

There is no need to quantify that with IMO Mike It's all about signal so yes, 'more signal helps' is a truth like a cow as we say in Holland. There is nothing special about O3 or S3, you need high SNR just like you do for L, Ha, RGB or whatever. If the photon flux is low you need to either expose longer, get more aperture or concentrate more angular sky on each pixel (lower F/ratio). It's the same same same as any other time where you want higher SNR. Naturally if you decrease the F/ratio through binning or reducers you loose resolution (as you said) and that's a tradeoff that may not be worth it.

So the best we can do is understand what's going on and decide which tradeoffs are the right ones.

[DMouse]

Thanks guys, I guess I am only just starting to scratch the surface with narrowband. I have seen images with 15min and higher exposures. I guess a bigger aperture would help as well. I am using a ED 110m with focal reducer, so about F5.6. I have a 200m Newt which is F5. So really I need to upgrade to more aperture and a lower F ratio, to really do decent narrowband.
Guess I am gonna be stuck with Mono Ha images mostly for now 

Clear Skies

Paul

[pfile]

well, in the case of IC1396 you can find many narrowband images, so OIII and SII should be possible.

but generally speaking the signal *is* weak so you will need long subs and lots of integration time. it is a surprise compared to Ha, this is true.

[Nocturnal]

Considering H is the most abundant element in the universe by far (neglecting dark matter for now) it isn't a big surprise Ha is most abundant too. Well, not to me anyway

[georg.viehoever]

...(neglecting dark matter for now)...

Imaging the most abundant material in the universe is even more difficult than OIII ?
Georg

[Nocturnal]

Ding ding! 

[DMouse]

Someone pointed me in the direction of the website http://www.sharplesscatalogue.com It has many narrowband images and details about them. Just looking at the integration times tells me I need lots more data, lots and lots more

Thanks for the input guys

[mschuster]

Be careful with the high-galactic latitude Sharpless regions. There are 8 of them, 2 are now considered planetary and the others dust reflection nebulae or photoluminescence of carbon in the clouds. Sh 2-24, 33, 36, 73, 122, 245, 290, 313. Hard to get Ha signal from these. IMO not much Ha in the Spring sky and Sharpless was over-trying to find something. I was overconfident on Sh 2-33, figuring I could get something in 3nm Ha. What got in 5 nights and 18 hours was mostly noise. A big waste of time. IMO luminance would have been more worthwhile.

https://dl.dropboxusercontent.com/u/109232477/PixInsight/serpens_2013_05_p.tif

Mike

[Nocturnal]

L is only worthwhile for targets that emit broadband radiation. Stars and therefore clusters and galaxies. L frames also contain all the light pollution and background radiation. Generally not desirable. Maybe I misunderstood what you meant though

[mschuster]

I think Sh2-33 is one of those broadband emitters. Dean Salman (sharplesscatalog.com) got a better result in less time with a clear filter. Sh2-33 is not a bona-fide HII region. I agree normally wideband gives more noise but at least for this object more signal too, and signal won. James Janusz (astroimage.net) also got a better result also in less time using a wider 8nm Ha filter. Optic and sensor differences are factors also of course.

Mike

[pfile]

Considering H is the most abundant element in the universe by far (neglecting dark matter for now) it isn't a big surprise Ha is most abundant too. Well, not to me anyway

thanks for sharing.

[jerryyyyy]

Thanks for this interesting discussion.  Have been out of town for a week and wish I could have had my scope on autopilot while I was gone to collect more H-alpha and O-III of M57... there is a lot of discussion of this object on CloudyNights currently.  Trying to image the outer halo.... quite challenging