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Hi,

A few nights ago I tried imaging the Soul Nebula. As this is only my first year I'm still thrilled just being able to locate an object etc. so this one was just for fun as I realise it was an imaging session of a faint nebula, with not that much exposure time for it - and with an 80 percent full moon, although half of the exposures, probably more than half actually were taken with the Moon below the horizon - whether that makes any discernible difference I don't know. As well as this I have no light pollution filters, or any filters for that matter and I'm using an unmodded DSLR. Therefore great expectations weren't in mind! However, I thought I'd have a go anyway, and every night imaging is another night of practicing everything else; Polaris, finding objects, setting up, etc. so it's not a total waste of time.

Anyway with that said, onto the image - I'm wondering why I have so much red in the image. Is it because some of it is from the effects of light pollution? Is there really that much red nebulosity there ? (I doubt it!) although I can make out the Soul Nebula, if I pull back on the red it affects not only all of the red around the edge of the frame but also in the Soul Nebula itself.

Am I doing something totally wrong with my processing ?  Or is it just that the data isn't that good anyway? I expect it's both but more so the latter but if anyone has any idea as to why there is so much of the red I'd be grateful to hear it.

 

 

Soul-Nebula.jpg

SC.thumb.png.4eefc15cc2fdaab49d8e5d23e0797e05.png

Edited by smr

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It would help if you can give people your camera settings - iso, exposure length, number of exposures etc. Also uploading your stacked image would let people have a go themselves at processing it.

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Thanks, good idea.

Camera settings - around 2 hours of mostly ISO 400 and some 1600 1 minute subs - mostly ISO 400 because apparently the Canon 80D is "ISOless" and there's no point in going past ISO 200 (even though I put it on 400 as I don't know exactly how accurate this is).

I took some exposures, not many, at 1600 as well just in case 400 wasn't pulling out enough data. I'm just reading up on which light pollution filter to get at the moment and I think this will help a lot. 

Anyway, the calibrated and stacked data is here. From reading my camera settings I'm guessing no one is going to bother !

 

Soul Nebula calibrated and stacked.TIF

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I had a look at the stacked image, and i don't think the image is too red. The colors were just not aligned well.
As far as ISO you're correct, the 80D is a bit special there. It's actually OK even at ISO100 for astro use it seems. However, i still think it's important to increase the ISO to get the signal above the noise floor if you're unable to do so by increasing exposure (correct me if i'm wrong).

I had a quick go at your pic trying to separate the soul. Far from perfect processing, but the soul is for sure there! :)
Did you check if your scope/camera/filter had dew on it? If not, then it looks like something might have gone wrong with your flat frames, causing processing to be more difficult. If both flats look fine and no dew on the scope, then i hope someone else can explain the uneven color and brightness.

Attempted to just align colors:
soul-raw.thumb.jpg.617ba23280cab8ba18fc8fd8e6212f70.jpg

Tried to correct the surrounding colors somewhat and pull out the soul:
soul.thumb.jpg.7d9b36adf167154668347306051c0825.jpg

 

 

 

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There seems to be quite a bit of light pollution, so a filter for that should help, but there's also a circular effect akin to vignetting but with darker and lighter rings around the centre, which may need some diagnosing.   

But there's data there.  

Out of interest, did you stack the different length subs together?  This can sometimes cause problems and for those targets where it's useful, layering them together after stacking can produce better results.

Quick'n dirty process in StarTools of the central area:

Soul Nebula cropped.jpg

Edited by almcl
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What scope do you use for imaging? I have been doing DSLR astroimaging for about two years, and in my opinion both DSLR and OSC cameras do not handle well light polluted (also with Moon) sky. Especially in the red emission nebulae subject. I was able to get some decent results under suburban sky (NELM about 5mag) but without Moon, and when the atmosphere was transparent. If conditions were far from good, then all red emissions were very noisy and bad quality. If you have bad LP or Moon in the sky you may try with something else, like open clusters. You will then have much background to sample and remove gradient, and processing should be easier. 

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9 hours ago, Jannis said:

I had a look at the stacked image, and i don't think the image is too red. The colors were just not aligned well.
As far as ISO you're correct, the 80D is a bit special there. It's actually OK even at ISO100 for astro use it seems. However, i still think it's important to increase the ISO to get the signal above the noise floor if you're unable to do so by increasing exposure (correct me if i'm wrong).

I had a quick go at your pic trying to separate the soul. Far from perfect processing, but the soul is for sure there! :)
Did you check if your scope/camera/filter had dew on it? If not, then it looks like something might have gone wrong with your flat frames, causing processing to be more difficult. If both flats look fine and no dew on the scope, then i hope someone else can explain the uneven color and brightness.

Attempted to just align colors:
soul-raw.thumb.jpg.617ba23280cab8ba18fc8fd8e6212f70.jpg

Tried to correct the surrounding colors somewhat and pull out the soul:
soul.thumb.jpg.7d9b36adf167154668347306051c0825.jpg

 

 

 

That looks much better than my effort. I managed to achieve what you did in the first image you posted by aligning the channels properly but as you can see it doesn't look good with all that discolouration. There was dew on some of the subs but how many I'm not sure, certainly many of them without dew. I noticed the dew not realising that it had built up and used a hair dryer  to get rid of it and then carried on shooting. I don't suppose there's a way to see which subs were effected by the dew is there? If there is I suppose I'd have to go through each of them manually and increase the exposure to see which ones had dew on and get rid of them?

The second image looks much better, basically what I was trying to achieve with just the Soul Nebula showing. Thank you. I didn't take any bias, dark or flat frames as I went (rightly or wrongly I'm not sure) with Roger Clarke's ideology of not using them as lens calibration in the raw conversion stage would mean they're not necessary? I'm interested in whether or not I should have used them though?

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2 hours ago, almcl said:

There seems to be quite a bit of light pollution, so a filter for that should help, but there's also a circular effect akin to vignetting but with darker and lighter rings around the centre, which may need some diagnosing.   

But there's data there.  

Out of interest, did you stack the different length subs together?  This can sometimes cause problems and for those targets where it's useful, layering them together after stacking can produce better results.

Quick'n dirty process in StarTools of the central area:

Soul Nebula cropped.jpg

Hi yes I'm not sure what's caused the vignetting either, lens profile corrections were used before stacking. I did stack the different sub lengths together, most subs were 1 minute at ISO 400. Some subs were ISO 1600 at 1 minute but some ISO 1600 2 minutes I was hoping these would pull out the nebulosity. 

 

Would I be better off just stacking all the 1 minute subs and disregarding the others then? Thanks for the processing, you can clearly see there is some data there.

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1 hour ago, drjolo said:

What scope do you use for imaging? I have been doing DSLR astroimaging for about two years, and in my opinion both DSLR and OSC cameras do not handle well light polluted (also with Moon) sky. Especially in the red emission nebulae subject. I was able to get some decent results under suburban sky (NELM about 5mag) but without Moon, and when the atmosphere was transparent. If conditions were far from good, then all red emissions were very noisy and bad quality. If you have bad LP or Moon in the sky you may try with something else, like open clusters. You will then have much background to sample and remove gradient, and processing should be easier. 

Hi, I use a camera lens for imaging at the moment - a 55-250 STM lens @ 250mm f/5.6.

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Just had a look at the subs - all sorts of different exposure lengths - thought I'd got mostly just 1 minute and 2 minute subs... but they are actually:

5 x 120s

105 x 60s

25 x 30s

and then 20 x 22/10//9/4/3/2 second exposures.

Would I possibly see better results getting rid of all except the 60s subs then?

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Why not stack all three separately and then examine them to see what sort of detail is there? 

If you are using DSS (although from the fact that you were able to stack multiple, different length exposures, you probably aren't) to stack, the scoring system can be used to pick out the dew affected lights and eliminate them from the final result.

I think the 30s might be good for small, tight stars but lacking in nebulosity, while the 120s might be better for nebula details.

If you aren't using flats (and regardless of the advice on the Clarkvision website) you may find that they will improve matters.  Bias could be helpful too.  Darks are less certain although they might help with the amp glow at the bottom corners, should you ever need the entire frame area.

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15 minutes ago, almcl said:

Why not stack all three separately and then examine them to see what sort of detail is there? 

If you are using DSS (although from the fact that you were able to stack multiple, different length exposures, you probably aren't) to stack, the scoring system can be used to pick out the dew affected lights and eliminate them from the final result.

I think the 30s might be good for small, tight stars but lacking in nebulosity, while the 120s might be better for nebula details.

If you aren't using flats (and regardless of the advice on the Clarkvision website) you may find that they will improve matters.  Bias could be helpful too.  Darks are less certain although they might help with the amp glow at the bottom corners, should you ever need the entire frame area.

I could do, I am using DSS to stack them all though and it stacked all the frames, I set it to register the best 95 percent of frames - maybe I should try a lower value?

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8 minutes ago, smr said:

I could do, I am using DSS to stack them all though and it stacked all the frames, I set it to register the best 95 percent of frames - maybe I should try a lower value?

Did you have DSS also set to align channels too?

Alan

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1 minute ago, Alien 13 said:

Did you have DSS also set to align channels too?

Alan

I can't be sure on that one as I've tried with and without recently but not sure on this particular stack whether it was on or off, I guess the colours can always be aligned in post anyway?

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As for dew; add all images of identical exposures in DSS and register them. Sort them by date and time, and you should usually be able to see quickly which of them to discard.

You'll see that most of then have roughly the same score, stars detected, and sky background %, - then suddenly stars detected will drop together with sky background % and probably also score. This is usually where dew or clouds are causing problems for you.
Discard ALL frames that stands out as significantly worse, or they will cause both a worse stacked image, and with uneven color and brightness.

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1 hour ago, Jannis said:

As for dew; add all images of identical exposures in DSS and register them. Sort them by date and time, and you should usually be able to see quickly which of them to discard.

You'll see that most of then have roughly the same score, stars detected, and sky background %, - then suddenly stars detected will drop together with sky background % and probably also score. This is usually where dew or clouds are causing problems for you.
Discard ALL frames that stands out as significantly worse, or they will cause both a worse stacked image, and with uneven color and brightness.

Thanks for this. In the 60 second exposures there were 5 frames with 0 score and 0 stars so I deleted them. 

Now the best frame is 306 stars with 21.43% sky background and score of 1590.99 which steadily decreases with the lowest frame being 111 stars, 18.94% sky background and score of 445.30

Is there a cut off point I should be looking for?

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If you're sure you sorted the list by time and not score, and it's decreasing steadily, then i guess it's possible that the dew formed slowly. It's also possible that moonlight/light pollution gradually caused more and more problems, but with that large difference (300 va 100 stars) it's less likely.

Personally i like to keep all frames except those that stand out as much worse then the average,  but in your case where DSS don't show a sudden change in the score that's not so simple to determine. I usually filter out those with significantly less stars detected, significantly higher sky background %, and significantly higher FWHM - then stack the rest.

In your case I would probably just quickly look trough the pictures and see if you can visually see any sudden changes. I would probably only keep the 105x 60s  exposures (and maybe the 5x 120s, stacked in a separate group in DSS) and discard the other 30/22/10//9/4/3/2 exposures.  

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Don't mess about with different sub lengths. Find out what works best in advance and go with that. (Some objects, and it really is very few indeed, do need subtle blending of different sub lengths but this is very, very unusual. This nebula certainly doesn't need them.)

After that, if you want to nail LP and other gradients effectively, your best best is Pixinsight and its Dynamic Background Extraction.

Olly

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13 minutes ago, ollypenrice said:

Don't mess about with different sub lengths. Find out what works best in advance and go with that. (Some objects, and it really is very few indeed, do need subtle blending of different sub lengths but this is very, very unusual. This nebula certainly doesn't need them.)

After that, if you want to nail LP and other gradients effectively, your best best is Pixinsight and its Dynamic Background Extraction.

Olly

Olly... recommending PI... what’s going on? I’m confused. 

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8 minutes ago, johnfosteruk said:

Olly... recommending PI... what’s going on? I’m confused.

...only last week he was enthusing about F-numbers ?... I’m really concerned.  ?

Seriously, though, I think that DBE has always been the weapon of choice for this.  It just seems bit churlish to buy PixInsight just for that and not use some of its other features too.

 

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7 minutes ago, AKB said:

...only last week he was enthusing about F-numbers ?... I’m really concerned.  ?

Seriously, though, I think that DBE has always been the weapon of choice for this.  It just seems bit churlish to buy PixInsight just for that and not use some of its other features too.

 

Seriously something wrong :) And you're absolutely correct of course, but gradientxterminator is a fair compromise if the OP uses Photoshop.

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I do and I do have gradientexterminator. Well worth it's price. Thanks for the replies guys. The data may not be brilliant by any stretch (I'm smiling as that pun has just come to me as I type) :D but I've learned a lot from your replies. 

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1 hour ago, Jannis said:

If you're sure you sorted the list by time and not score, and it's decreasing steadily, then i guess it's possible that the dew formed slowly. It's also possible that moonlight/light pollution gradually caused more and more problems, but with that large difference (300 va 100 stars) it's less likely.

Personally i like to keep all frames except those that stand out as much worse then the average,  but in your case where DSS don't show a sudden change in the score that's not so simple to determine. I usually filter out those with significantly less stars detected, significantly higher sky background %, and significantly higher FWHM - then stack the rest.

In your case I would probably just quickly look trough the pictures and see if you can visually see any sudden changes. I would probably only keep the 105x 60s  exposures (and maybe the 5x 120s, stacked in a separate group in DSS) and discard the other 30/22/10//9/4/3/2 exposures.  

Ah I think I was sorting them by score and then star count. I can see a column for date/time but it only lists the date and not the time, whether that's because I've calibrated them first I don't know as it also doesn't show me the values in the ISO and Exposure column. I guess sorting them by filename would be the same as the time? ie. IMG_9454, IMG_9455 etc. ? As aforementioned these subs are all 60s.

 


dss.thumb.png.98d84b4e581ddaca661737b5874d1721.pngdss2.thumb.png.a8d4a443935dc74f4ce247c89183712d.pngdss3.thumb.png.ee012014300994b58644751029f0c08a.png

Edited by smr

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