Jump to content

sgl_imaging_challenge_2021_2.thumb.jpg.72789c04780d7659f5b63ea05534a956.jpg

Recommended Posts

Nice one Paul.

These days I am working on the principle that everything that comes through the Sii filter will also be evident in the Ha sub's, and that by a bit of mathsy cleverness it should be possible to get whatever signal there is in Sii in a lot shorter time. Would you agree? (And can you come up with a formula?? :D )

Cheers

Tim

Link to post
Share on other sites

Thanks all. This was my 5th version. With no clear skies up here I have taken to messing about, trying different methods and techniques. I think I am getting better even without using any photoshop. Just maxim and ImagesPlus 2.8...well behind the times now!

My normal method for NB is to stretch each channel individually and then combine and adjust. Normally I process Ha first but this leads to me maxing the HA data and in response murdering the SII and OIII. In this case I processed them first then the Ha to match. It stops the Weak channel from being blown out by the much stronger Ha.

Tim, I agree that normally there is Ha present wherever there is SII, but the can't be anyway to extract its signal. Looking through the Ha only shows the Hydrogen, there is no information present about the distribution and relative intensity of the SII. For example in the outer part of the rosette. Here, it is quite red, but the hydrogen only data could not show that. You are trying to get something for nothing. A valiant effort but the universe never allows that. When you image SII you are looking at how it is distributed. Even looking at the spectrum of the object you could scale the Ha by the ratio of the strength of the emission lines, but you will not give you the distribution of the sulphur, just it's relative brightness. You would need an pixel by pixel spectrum to properly to work out how the scaling varies across the object. In the time you have done that you could have gathered lots of data through the filter!

You could take an image in the R filter and the Ha and suppose that the R filter contains the Ha plus the SII. On subtraction then the SII remains. This would be a very odd way of doing it and will be less accurate and I'm sure noisier.

So no great equation here.

I would say that to maximise the SNR for sulphur and for anything is, as you are already aware, use as long subs as possible. Limit the number of reads the camera has to do. That along with darks and flats. One more thing that could be done is to spilt you imaging time sensibly (not implying for a second that you are not already), but as you will be aware, the OIII and SII are much fainter and so require more time. Rather than use an equal weighting of exposure time, bias it towards the OIII and SII. Perhaps in the ratio of 1:2:2. That's what the above image has, and even still the limit factor was the faint data not the Ha. And that's for an object that I think is quite bright in all 3 filters.

There's no real secret with all this. No clever mathematical post processing trickery. The secret to good images will always start with good data. Good data has a high SNR achieved by a myriad of things including image calibration and long subs.

I'm afraid I haven't said anything that wasn't already known but that's my understanding of the world.

Cheers

Paul

  • Like 1
Link to post
Share on other sites

There has to be a way!!!!!! :D

Granted it might not be the most scientifically accurate representation, but I bet that a 60second Ha sub would be hard to differentiate from a 30 min Sii. I didn't bother getting a 2" Sii filter for this camera.

One object where brief Sii sub's are awesome is M42's trapezium. Long focal length 1-2 seconds reveal amazing details.

Cheers

Link to post
Share on other sites

Even still, it would have the same spatial distribution. It wouldn't be able to highlight the compression areas. It's ok for Hbeta as it will have the same distribution as Ha only at a reduced intensity (in the absence of dust).

Agreed with Orion, the bar near the centre shows up well in the S2 image. As an experiment why not take an Ha image and make it look like the S2 image that you have for the same object. Not just the same brightness but the brightness in the same places.

I'll bet it is extraordinarily difficult to make the Ha look virtually identical to the Ha.

To get this right without knowing what the S2 should look like is impossible. You can't tell where the S2 should be and how strong it is.

It is more than just a simple scaling.....

Best of luck

Paul

Link to post
Share on other sites

Very nice Paul, this one is still stuck behind a tree for me so its going to be probably next month before I an have a serious go at it.

Interesting discussion on SII, but like you said I cant see there being any way to extract it from Ha. You may as well ask to deconstruct Luminance - still just as impossible! :)

Perhaps another way to approach it would be to bin the SII depending on focal length, and whether it adds any structure (in which case, its unavoidably 1x1). If SII present in the Ha, then you only really need to highlight those areas with a higher concentration of SII, and arent required to add any further detail (which is carried in the more abundant Ha layer).

Edited by Uranium235
Link to post
Share on other sites

I don't know if there is any benefit in making a pseudo luminance from Ha+S2+O3. Rather than a 1:1:1 weighting you could say 0.5Ha+2O3+2S2....or something like that.

Thought should help emphasize the weaker lines, but I'm not sure if it would look daft. Might give it a look.

Paul

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.