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SlimPaling

Sh2-155 ... first attempt at narrow band imaging .. a lot to learn !!!

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My first attempt at narrow band imaging .... and I realise that I have a lot to learn !!!!  I almost didn't upload my efforts but I am interested in what folks might say about it.

I knew that Sh2-155 was going to be quite faint and didn't know how much detail was going to show up in my stacked images. I had to really over stretch the 3 sets of stacked files to find any details ... hence a very "grainy" final image .... but at least I could see something!

I only did 7 x 300sec Ha/Oiii/Sii sets of images.

I could see quite a bit of detail in my Ha set .... a VERY faint smudge of detail in the Sii set ... and absolutely  nothing in the Oiii set. I have tried to use the Hubble Pallet but  can see that the Ha channel totally dominates.

 

774872165_FinalJPEG02Dec2020.thumb.jpg.87462434cf9d5cd1276301b879106b4e.jpg

Obviously I need to increase imaging times from 300sec .... my mount is capable of 1200 sec and beyond. .... and I need a lot more images stack.

I will be adding more to my initial set of images as time and weather allows in the hope that I can improve my final image.

Mike

Edited by SlimPaling
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Mike, it looks like you are on track.  You have't chosen an easy target though!    As you say, you need much more exposure time and longer exposures.  I see you are using a CCD camera so you need to be aiming for at least 1200 seconds for Ha to overcome the read noise.  You can always bin the signal poor channels and then 5mins should be ok.  I think the main difficulty with NB imaging is getting over the notion that a clean, Hubble palette image can be completed in a single night.  Think of this as a winter project.  The processing sets a whole new collection of challenges.  The main issue is harmonising the channels given the huge difference in image stretches between Ha, OIII and SII.  Your image is very green so you probably need to push the OIII and SII a lot harder.  This then creates issues such as horrible star halos, odd colour casts and colour noise.  There are techniques to address all these issues in PS and PixInsight.  Keep working on gathering more data.  I would be very interested to see how you get on.  If you post again and don't get much of a response (the reply rate on this board can be a bit random!) send me a pm.

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57 minutes ago, MartinB said:

Mike, it looks like you are on track.  You have't chosen an easy target though!    As you say, you need much more exposure time and longer exposures.  I see you are using a CCD camera so you need to be aiming for at least 1200 seconds for Ha to overcome the read noise.  You can always bin the signal poor channels and then 5mins should be ok.  I think the main difficulty with NB imaging is getting over the notion that a clean, Hubble palette image can be completed in a single night.  Think of this as a winter project.  The processing sets a whole new collection of challenges.  The main issue is harmonising the channels given the huge difference in image stretches between Ha, OIII and SII.  Your image is very green so you probably need to push the OIII and SII a lot harder.  This then creates issues such as horrible star halos, odd colour casts and colour noise.  There are techniques to address all these issues in PS and PixInsight.  Keep working on gathering more data.  I would be very interested to see how you get on.  If you post again and don't get much of a response (the reply rate on this board can be a bit random!) send me a pm.

Hi Martin ...

Many thanks for taking the time to send me your thoughts .... much appreciated 🙂

I am intending to add more data if the weather allows using longer exposures ... I  prepared my 1200 sec Darks last night in anticipation.

There are a couple of things that I would like to ask about in your message ... I have highlighted them in the your quote above.

(1) I don't understand what you mean by "bin the signal".   I have only ever used " 1 binning" as I do not understand how to use other binning settings once I have got them!

(2) At the minute I can't cope with PI ( as I find it mind blowing despite me trying to understand it when I get a few spare minutes ) ... I only use PS for my processing. I use Noel Carboni's actions extensively and also Annies actions occasionally .... are these the techniques the "techniques" that you are hinting at? ... or are there more techniques that I don't know about?

Thanks for offering to take pm's from me if I need a few more bits of advice 🙂

Cheers Mike

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Your capture software should allow you to configure your camera to group pixels together.  Binning x2 means that 4 pixels (2x2) are used in unison.  For a given exposure a binned pixel collects 4 times the amount of light.  4 pixels are read as one which means that read noise is quartered.  The optimal minimum exposure is that which is long enough for the signal from background sky brightness to swamp the read noise.  This time is quartered when pixels are binned x2.  The downside is that your resolution is also quartered.  This is unlikely to be a major issue for OIII and SII unless the target has lots of fine detail in these channels e.g. The Veil Nebula.  So it can be quite a good strategy to use unbinned for Ha and binned for SII and possibly OIII.  This can be a real time saver and allow you to get more precious Ha.

Most of my processing is done in PS.  I am becoming more au fait with PI and can see its merits but many many APOD images have been processed in PS!  Some good info on colour balancing here http://bf-astro.com/hubbleP.htm  The best method of reducing magenta halos is to install a free plug in called HLVG http://www.deepskycolors.com/archive/2010/04/26/hasta-La-Vista-Green.html  This can be used to eliminate or reduce green but also, if you invert your image ctrl-i to give a negative, apply HLVG and reinvert the magenta halos magically disappear!

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Hi again Martin .... thanks for your quick reply to mt two questions. Yes my capture software is capable of doing different binning levels.

I use MaximDL to calibrate, align and stack my DSO images before taking these into Photoshop.

So am I correct in thinking that MaximDL can align and stack images that have different binning levels? .... or do I have to do something to the x2 binned images before I align & stack them?

Cheers Mike

 

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I'm not sure whether Maxim will automatically rescale during alignment or not, I suspect it does.  I use Maxim as well.  There are different ways to get everything lined up properly.  The simplest way  is to stack and combine the binned and unbinned seperately and then get Maxim to double the size of the binned image.  Then use the align tool to match up the two images using the unbinned image as a reference.  I used to bin SII but more often than not, these days, I just don't bother with SII and create a synthetic channel to replace it.

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On 04/12/2019 at 15:49, MartinB said:

I'm not sure whether Maxim will automatically rescale during alignment or not, I suspect it does.  I use Maxim as well.  There are different ways to get everything lined up properly.  The simplest way  is to stack and combine the binned and unbinned seperately and then get Maxim to double the size of the binned image.  Then use the align tool to match up the two images using the unbinned image as a reference.  I used to bin SII but more often than not, these days, I just don't bother with SII and create a synthetic channel to replace it.

Hi again Martin ...

I have managed to get a few x2 binned Sii and Oiii images now ( more to be added when the weather allows ) .... but haven't even tried to process them or stack them with my single binned 1200 sec Ha files yet.

Can I ask a question ...? 'cos this is quite new to me 😞

Re: the these x2 binned images ... because 1 pixel is turned into 4 pixels ... isn't the resulting image a quarter size of the single binned images? Therefore I will need to carry out Maxim's "Double the size" process twice to get it the matching size to my single binned Ha images?

Cheers Mike

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The image is half the size - don't ask me how cos I don;t know why Lol.

Yes you will need re-sizing software.

Carole 

 

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1 hour ago, SlimPaling said:

Hi again Martin ...

I have managed to get a few x2 binned Sii and Oiii images now ( more to be added when the weather allows ) .... but haven't even tried to process them or stack them with my single binned 1200 sec Ha files yet.

Can I ask a question ...? 'cos this is quite new to me 😞

Re: the these x2 binned images ... because 1 pixel is turned into 4 pixels ... isn't the resulting image a quarter size of the single binned images? Therefore I will need to carry out Maxim's "Double the size" process twice to get it the matching size to my single binned Ha images?

Cheers Mike

The binned images are 1/4 the area but the dimensions are halved.  The doubling relates to the dimensions rather than the area.

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1 hour ago, carastro said:

The image is half the size - don't ask me how cos I don;t know why Lol.

Yes you will need re-sizing software.

Carole 

 

Thanks Carole for you thoughts 🙂

Actually I have been "playing" with MaximDL a bit earlier and I tried to align a single binned Ha tiff with a x2 binned Sii tiff ( without any resizing) too see what happened.

It worked in a wink ... no problems ! Both files aligned and the Sii tiff was automatically resized without me doing anything extra 🙂

Things are looking up!

Mike

 

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47 minutes ago, MartinB said:

The binned images are 1/4 the area but the dimensions are halved.  The doubling relates to the dimensions rather than the area.

Thanks Martin .... my maths wasn't too good was it!

I need to re-do my 11plus exam!

Mike

PS: did you see my comment to Carole, just now, saying I have discovered that Maxim does do automatic resizing when stacking with single binned images?

 

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I thought it probably would.  Maxim's stacking routine is very user friendly. 

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