m42 - Orion's Nebula - first attempt at multiple exposures + stacking. Please critique

[pie_in_the_sky]

Hi all,

Pretty sure this is a thing (asking for critique), if this should go somewhere else please let me know.

As the title says. Brand new to astro photography, this was my 6th session but 1st 'proper' session with tracking and multiple exposures (and an actual target vs. poining the scope at random parts of the sky). I was lucky enough to have 3 nights of clear skies so was actually 3 sessions combined:

Context:

• Bortle class 4 location (according to https://www.lightpollutionmap.info/)
• Approx. 60% moon
• Camera: Unmodified Canon 700D / T5i
• Scope: RedCat 51
• No filters
• No guiding
• Mount: Sky Watcher Star Adventurer GTi
• Camera settings: manual mode | manual focus | RAW | white balance: daylight | ISO 800 | Shutter: 30 seconds | total lights: 350 | Overkill calibration darks, flats and biases - about 300
• Photos stacked in Siril - some processing of the background to level out light pollution. More complete processing in Photoshop - separation of stars and nebula. Stars slightly subdued. Nebula darks and midtones adjusted with colour vibrancy added (more was done but these are the broadstrokes). I had to reaquaint myself with mask layers but it really helped bring the core back.

Perhaps an obvious one but two star alignment really improved the initial goto and tracking (although goto is still some way out and needs manual adjustment).

Really keen to hear your thoughts, tips for improving (tech or process). I'm keen to know - based on what I've put in the detail above, what change do you think would have the biggest impact?

Ta

[Elp]

I'd say that's pretty good.

The one thing I'd say, focus seems ever so slightly off unless if you've blurred the star layer in post.

You don't really need that many calibration files (more is better) but I typically only do sets of ten to twenty, never had a problem with this many. Usually with Canon you don't use bias, you subtract a fixed value when you do your calibration in Siril but your image has turned out fine.

 

Edited January 27 by Elp

[pie_in_the_sky]

Thanks Elp.

Yes, I feathered the star layer - from memory I think I also made them smaller too. I'm not happy with the large stars just below the nebula - although I do like the apparent depth they provide.

With a week of cloud forecast I might re-run processing and try some different approaches.

Ha - I thought it might be overkill. It was more to get muscle memory and get the process down. Will bear that in mind later though thanks.

[ONIKKINEN]

First proper image, stacked from 3 nights, new to the hobby, did i read that right? 😲. I think i should ask you some advice on how to do all this! Seriously, you've skipped like a year or two of an average imagers learning path - quite impressive.

The image is spectacular for a first shot like this (and actually its a good image even if it were your 50th one), i really cant find anything specific to critique about it.

Couple of small things that could be improved, but no big deal. The core is blown, like it is often in M42, you could try to take some shorter exposures just for the core and mix them in with this one to recover the saturated parts. If your raw lights are not saturated then you can recover the core by simply not stretching so hard, but you'll likely still need to play around with layers to blend the core to the rest of the image.

And maybe the nebulosity could use a touch of sharpening, but this is often a matter of taste so up to you.

[pie_in_the_sky]

Cheers Onikken, really appreciate that feedback - yep brand new but lucky that I had a pretty open December and January so lots of time for reading and just practicing getting polar alignment. I had basic understanding of cameras and photoshop which was a huge help too.

I also tested the patience of the team at First Light Optics to the limit with a ton of questions

I completely messed everything up to begin with. I didn't realise the scope was only for deep sky, my camera couldn't attach to the redcat, my tripod was wrong etc etc. The folk at FLO helped so much.

Good point on the core - I thought I'd cracked it with a darker exposure and a layer mask. Do you have a good example of a non-blown core? I'll give it another go. I also have the picture below where I took the vibrancy much higher. This feels a bit over processed to me though.

[pie_in_the_sky]

Oh - when you say nebulosity, does this mean sharpening up the nebula itself. I.e. adding clarity in photoshop or similar?

[ONIKKINEN]

26 minutes ago, pie_in_the_sky said:

Oh - when you say nebulosity, does this mean sharpening up the nebula itself. I.e. adding clarity in photoshop or similar?

Smart sharpen or unsharp mask in Photoshop would be my first choices, applied with masks on the starless layer where you want them, so you can ignore the background that has nothing to sharpen and will only gain noise from this. You may also want to try that for the star layer, if you would like your stars to be more hard (matter of taste i think, although i like yours). Something like 1.5-->2 px width for the filter and then dial it in with the percentage

Texture and clarity in camera raw or lightroom is more of a contrast tool, not exactly the same as sharpening but you might want to try that too and see how it changes the image.

27 minutes ago, pie_in_the_sky said:

Good point on the core - I thought I'd cracked it with a darker exposure and a layer mask. Do you have a good example of a non-blown core?

There should be some detail to the very bright core if done right - but it is tricky to do right i will say and most images have the core saturated. I have shot M42 only twice, and i think both times the images sucked and yours is better but this is what the core might look like if it were not blown:

As for how to blend that with the main image you'll need to get creative. You could use the blend mode darken for example, and tweak the core layer in a way that it blends nicely to the surroundings. Another way would be with layer masks - or by simply deleting the core with the color range tool and having the unblown layer below. Many ways to skin the cat, but all will need some experimentation.

[WolfieGlos]

Agree with everyone else, that’s a great first image. Well done 👏

Onikkinen posted an example before I found mine to link, but here’s an example I did without the blown core. Although it is a bit brighter, I can’t recall if I used masks for this, but it’s just about getting a natural look to it. The aim is to try and show the trapezium cluster of stars at its core - which will only really be visible if the core isn’t blown.

Look forward to more of your work 🙂 

[pie_in_the_sky]

Yep - camera raw were the settings I was thinking about but unsharp makes more sense. I will have another go.

Ah, right so the core definitely is blown out - they are actually individual stars and not just a bright cloud...right ok, that makes sense. I'm definitely going to experiment with stacking or blending in some lower exposure images. I think all of the images I currently have are blown out so will wait for the next clear sky.

Seems obvious now but I didn't realise how obsessed I'd become with weather reports

Can I sneak in a quick follow up question. During processing in Siril, I looked at the histogram preview and saw the image below. Is the white glow from bottom right light pollution or did I make a mistake somewhere?

[pie_in_the_sky]

Thanks Chris.

Ah yep - I mentioned in the other post that I thought the core was just a bright glowing cloud (I've got a lot to learn!) so this is really helpful. This is going to be tricky to get right. I'll see what I can do and hopefully post a follow up.

[ONIKKINEN]

9 minutes ago, pie_in_the_sky said:

Can I sneak in a quick follow up question. During processing in Siril, I looked at the histogram preview and saw the image below. Is the white glow from bottom right light pollution or did I make a mistake somewhere?

Gradient from the sky, from both light pollution and Moonlight but in your case at bortle 4 the 60% Moon is a larger contributor to this than the light pollution

Background extraction will get rid of it, but i think you already got that since the gradient is gone in the processed image.

[pie_in_the_sky]

Thanks Onikkinen

[geeklee]

What a great start @pie_in_the_sky !  Nicely balanced, good background, nothing pushed too hard (core aside) and some of that faint dust showing through all over in the first image.  Some great feedback from the other posters already 👍

[pie_in_the_sky]

Cheers Lee. Blown away by the comments. I liked the pic myself but had thought there would have been lots of issues pointed out. Chuffed overall.

I'm going to revisit the core and see if I can improve - itching to capture something else though.

[pie_in_the_sky]

@geeklee Hijacking my own thread to ask - I've just been looking at your Astrobin. Some fantastic pictures in there! I really like the mono pics.

How do you end up with colour pics with a mono camera. Is this done when the picture is taken - wondering if you use RGB filters with the scope / camera or is it done in post-pic processing? Do Ha filters dual purpose boost light from nebulau and filter light pollution - or does this depend on the particular Ha filter?

[geeklee]

4 minutes ago, pie_in_the_sky said:

How do you end up with colour pics with a mono camera.

It's as you describe - particular filters with a mono camera but combined in software afterwards.  From a traditional R, G & B filter perhaps, adding Luminance, or using narrowband filters.  Narrowband filters are typically Ha, OIII & SII then adding these in the R, G or B channels of your choice (like the common Hubble SHO palette - SII into R, Ha into G and OIII into B).

6 minutes ago, pie_in_the_sky said:

Do Ha filters dual purpose boost light from nebulau and filter light pollution - or does this depend on the particular Ha filter?

They don't boost anything as such but block all other wavelengths of light, thus giving you just the wavelength of the filter.  Definitely one reason why some shoot narrowband only in light polluted locations.  You also get multi-narrowband filters that can be used on OSC (One Shot Colour) cameras to help capture certain objects.

8 minutes ago, pie_in_the_sky said:

I really like the mono pics.

I really like Ha images.  Ha is usually the filter that gives me the biggest smile when a sub comes in   It never fails to do this for me.

Apologies if I glossed over some of the above - I didn't want to info dump.

[pie_in_the_sky]

Ok, this is interesting. A great rabbit hole for me to go down.

Is 'one shot colour' what you call a colour camera that captures all colours in a single frame?

The Ha filter can be used in one shot colour cameras too right (assuming my definition of one shot colour is correct)? I mean it's not just for mono.

It looks like you can capture more fine detail with mono - I assume some overhead related to colour capture is avoided. Perhaps it's just a perception thing due to contrast levels.

Last question (not a guarantee ) - does using a mono cam mean that your photo count is tripled (when using 3 filters)? I.e. you have to take the same pic with each filter.

Mono kit is definitely something I will look into when it comes time to upgrade. I can't put my finger on it but there's something about those pictures...

[ollypenrice]

As others have said, this is a great start. You picked a popular but very difficult target, the only one on which I've found multiple exposure lengths to be unavoidable. Combining them is quite a complex process but can be done.

If you don't have any short exposures you can use a very soft stretch to replicate them. How blown is your core in the linear image? It cannot be 'de-blown' but there is no reason for the brightest parts to get any brighter. This is a good photoshop tutorial. https://www.astropix.com/html/processing/laymask.html  This is the method I always use on M42 to produce something like this: https://www.astrobin.com/321869/B/?nc=&nce=

Exposure time in One Shot Colour and Mono? There's no free lunch.  An OSC captures red on a quarter of its pixels, green on half its pixels and blue on a quarter of its pixels. It might be better to replace the term 'one shot colour' with the rather cumbersome, 'quarter of a shot red, half a shot green, quarter of a shot blue.' When a mono shoots through a colour filter it shoots that colour onto all pixels. There's not much overall difference in that respect. On faint targets, though, a mono can shoot luminance on all pixels and this picks up faint signal very fast. You don't actually need as much colour as luminance so mono starts to pull away. It's also much faster in narrowband.

In theory there is a slight resolution advantage in mono but, in reality, you will be very unlikely to be able to see it.

Olly

[pie_in_the_sky]

Thanks Olly. I had included steps similar to that - using a layer mask and the brush tool to take down opacity on the blown out, stretched layer for the less stretched one below. The issues are that a) I didn't know what the core should look like, going back through my layers I can see that I accidentally discarded some of the detail in the core...but b) even the linear pic has the core blown out. I'll definitely combine this approach with some shorter exposed stacks to try and bring it back. Thanks for the info - your version is great!

Mono definitely seems the way to go, although I think it will be some time before I upgrade.

Now to persuade my other half that we need a family holiday in the South of France

[geeklee]

Olly has kindly picked up those queries but on the filter,

14 hours ago, pie_in_the_sky said:

The Ha filter can be used in one shot colour cameras too right (assuming my definition of one shot colour is correct)? I mean it's not just for mono.

It can, but for OSC cameras it's more popular to get a multiband filter (the most common being duoband, that have peaks in Ha and OIII).  These multi band filters at least help the challenge Olly describes by making the most of an exposure - getting Ha onto Red and OIII onto Green/Blue (depending on the pass bands of the filter) at the same time.

14 hours ago, pie_in_the_sky said:

does using a mono cam mean that your photo count is tripled (when using 3 filters)? I.e. you have to take the same pic with each filter.

That's right, each filter needs sub exposures to make a final integrated stack, per filter.  These are then combined software.  An example of a final stack of R, G & B filters:

Combined and processed.

Hope this helps.

[WolfieGlos]

1 hour ago, geeklee said:

That's right, each filter needs sub exposures to make a final integrated stack, per filter.  These are then combined software.  An example of a final stack of R, G & B filters

That’s a nice image of the coat hanger Lee, look at the colour in that background of stars!

I hope I’m not hijacking pie’s thread, but do you shoot flats for each of filters? If so, do you do it with an integrated/moveable flat panel, or do you shoot them after the session?

Im currently in a similar boat to 900SL was in his thread and the cost of mono seems to keep adding up - which may be relevant for pie in the future if he’s thinking of mono. If I went for the 533mm pro with 1.25” LRGB filters and EFW it’s currently circa £1500, but with a moveable flat panel (deep sky dad) it’s more like £2000. That’s without narrowband filters. For that money alone, a 2600mc with dual band Ha/OIII and SII/OIII filters seems more reasonable! 

Back on topic, another guide for M42 is this one on sky at night, that I used the first time I imaged M42. It may or may not be of use depending how you get on with those excellent guides Olly linked. 

[geeklee]

5 hours ago, WolfieGlos said:

but do you shoot flats for each of filters? If so, do you do it with an integrated/moveable flat panel, or do you shoot them after the session?

Yeah, I shoot flats per filter - including LRGB.  I shoot the flats another day (before or after) and try and use them for as long as possible!  This particular setup was a RedCat+294MM.  I work towards getting the whole train as free from dust as possible, then shoot flats.  While I setup and tear down for every session, the imaging rig (scope, EFW, camera, guide scope etc) are always kept together so this flats approach has worked well for me so far.

For my reflectors with dew shields I'm even more careful with mono but am more amenable to shooting flats on an OSC each session.

My process is just a flat panel I place on top after slewing to zenith - nothing fancy.

5 hours ago, WolfieGlos said:

533mm pro with 1.25” LRGB filters

While I know all the pros and cons, I still find (L)RGB imaging in the UK frustrating at times and rarely do it.  It's the narrowband filters where I find so much joy and gains on mono.  I find HaRGB images very attractive though.

5 hours ago, WolfieGlos said:

533mm pro....a 2600mc

What a choice!  I enjoy both these cameras - the FOV on the 2600MC just blows the 533MM out the water of course but I enjoy using the 533MM on longer focal lengths where I'm looking for a tighter crop anyway. 

Hopefully something in there that helps!

[pie_in_the_sky]

Hope you don't mind me resurrecting this post but I took the feedback and a) captured another set of lower exposure photos of the core; b) completely reprocessed to incorporate the overall feedback and also blend in the core.

I'll drop the original in first so a before and after is easier. I think this is the best I can do with current gear, as always though feedback more than welcome. I know there is a colour cast on the background of the new image. Background in general is a bit funky, I focused solely on the nebula plus the background artefacts are due to manually aligning the original image with the new, differently framed low exposure version and then blending them together.

Cheers

original

new version, reprocessed + core