Finally, my first proper imaging session, would like some capture/GiMP pointers

[blameTECHIE]

After what feels like an age, I've now finally managed to figure out my steps to getting consistent polar alignment and guiding.

Not the best time of year to be trying with the short UK nights, but here's the result of my first imaging session.

C12 Fireworks Galaxy 30th May 2021 2345BST (ish) start

EQ6R with SW ED80DS Pro; PHD2 guided, SharpCapAltair HyperCam 183C via SharpCap 12bit FITS 1x1 binning for 16x 600s, 400 gain
Stacked in DSS with Darks (not 180s though) & Flats taken via NINA.
Noticed there's some AMP glow from the HyperCam which is known about for these, better (longer) darks should hopefully take care of that.
Will probably stick with the same target on my next session but try to remember to use the 2x Barlow I have  
It's all a bit of overload for me right now with having finally captured something that a)guided correctly b)stacked correctly and c)actually has a DSO in it.

But I'm stuck with GiMP, so am keen for any comments on post-processing or changes to initial capture, for now I've just applied 'Auto Input Levels'

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The problems; well Stellarium/EQ6R sync is off, but that's another issue temporarily solved by platesolving and then adjusting the stellarium target accordingly guess where the object will be. 

Edited May 31, 2021 by blameTECHIE

[geeklee]

Great start @blameTECHIE Very challenging time of year to be going after these sorts of targets but you've got some great detail and structure in the galaxy.

Sorry I can't help with GIMP, but for the darks, as you've hinted at, once you get exposure and temperature matched versions it should remove that amp glow fine.

 

 

[blameTECHIE]

Thanks @geeklee - just setting up now to run the darks, think I've a good couple of hours before any imaging tonight - one advantage of a cooled camera I guess

[geeklee]

10 minutes ago, blameTECHIE said:

one advantage of a cooled camera I guess

Absolutely.  A job for a cloudy day/night and one you don't need to do that often.  If you're grabbing 180s darks today, you just re-use them - I think it's typical to keep using them for 6-12 months.

For tonight, I would stick with this FOV and just add more data of the same area (if possible to get the same framing with your current toolset).  I don't think the barlow is going to do everything you want - it may increase the focal length, but at the serious detriment to speed, more challenging guiding and maybe more.  I have to admit, I haven't seen anyone use a barlow for DSO imaging (it sounds too good to be true if you could!) but I'm sure there are exceptions... and if you like to experiment of course!  

Edited May 31, 2021 by geeklee

[blameTECHIE]

thanks again - and fully understood.
I'll get these 10min darks done and will revisit the same framing if I can.

Was thinking of dropping down to 5min exposures so I wouldn't lose so many frames tonight to satellite trails, but probably best I just stick with what has worked for now.

[geeklee]

1 minute ago, blameTECHIE said:

Was thinking of dropping down to 5min exposures so I wouldn't lose so many frames tonight to satellite trails, but probably best I just stick with what has worked for now.

I wasn't sure if you meant 180s or 600s in the first post as you mentioned both but was going to say 600s on a CMOS camera in broadband is high.  I think it's worth reducing it - there is some concrete calculations to work out the best exposure for your sky conditions, target and camera.  Starting out, I'd just bring it down a bit - 5 minutes if you're happy with that, but even 1, 2 or 3 minutes in our non-astro dark skies should be fine.  The satellite trails should get removed in stacking if you have enough subs - another reason to reduce the exposure + less reliance on perfect guiding over that whole exposure (although you have a solid mount).

If you've not already seen it, one to watch over the summer / cloudy nights. https://www.youtube.com/watch?v=ub1HjvlCJ5Y&ab_channel=SharpCap

 

 

[blameTECHIE]

to be honest, I'd been messing about with profiles in SharpCap and not realised until I was a couple of images in and just thought I'd leave it as an experiment and reduce next time if necessary.

Also thought it might be a good test to see how well I'd finally got PHD2 guiding and, at least for last night, I think I managed a reasonable alignment.

Thanks yet again for the pointers - I thought I'd watched all the yt vids and read bits and pieces over the last six months but it all went to pot when I actually had something that was working .... will drop down to 5mins tonight and get those darks taken before I start for a change  and think about actually planning things for a change rather than dealing with poor focus or lack of PA etc.

And thanks for the link - added a new bookmark for that vid and will pay close attention.

Kev

 

[blameTECHIE]

Thanks again @geeklee for the support.

Managed 88x 3min frames last night with a really close alignment.  DSS using 80% of frames produced this:

which, with a little bit of GiMP (no idea what I was doing, but know I need to do something to bring out C12 from the starfield), produced this:

and, for my first DSO with a proper rig (i.e. not my one attempt at Andromeda with a DSWR/Star Adventurer) quite chuffed with how the 100% image compares with Stellarium's DSO image.

Got loads to learn still I know but already looking forward to another clear night and a new target.

(please excuse the screengrabs, but produced nice small filesizes for sharing)

[geeklee]

28 minutes ago, blameTECHIE said:

Managed 88x 3min frames last night with a really close alignment. 

Great stuff 👍 You have every reason to be pleased with the outcome!

Be careful of clipping the black point - it was marginally done in the first image, but seems more severe on this one looking at the histogram (primarily in the blue).

Keep an eye on dew and/or flat calibration - I only mention this as there's a slight gradient and a brighter area in the middle.  One more thing to add to the thousand other things we need to think about / learn about for each following session 😅

 

[blameTECHIE]

only a thousand other things?! 🤣 

I checked my imaging settings and had changed the black level (I think this is offset) from 3 to 30 somehow, that's been put back, for now, set to 0.  I was hoping to not have dew issues, but then my heater band is a cheap amazon one with very little control, but thank you, something I can look for an upgrade to over the summer - I'd been staring at the image for so long I was doubting myself as to whether I was seeing it or not.

And when I've got all this lot working I've still got all the other things hidden in the garage to play with (ZWO OAG, AutoFocuser, Filter Drawer and of course the C9.25 OTA) - should keep me busy for years, much to the other half's relief no doubt 🤭

[iapa]

On 31/05/2021 at 20:07, blameTECHIE said:

Thanks @geeklee - just setting up now to run the darks, think I've a good couple of hours before any imaging tonight - one advantage of a cooled camera I guess

I tend to cool my camera to the temperature I intend to use, then put my camera in the fridge - it reduces the strain on the camera cooling - and then take a couple of hours of c40 frames at different exposures; usually 600, 300, 240,120, 60 and 30 seconds.

These are used for about 6 months, then I take another set.

I also do a set of BIAS frames at the same time.

Flats and flat darks I do at the end of a session with a light panel.

There are different recommendations for use of calibration frames for CCD/CMOS cameras, so I just take every thing then try the combinations.

[geeklee]

37 minutes ago, blameTECHIE said:

And when I've got all this lot working I've still got all the other things hidden in the garage to play with (ZWO OAG, AutoFocuser, Filter Drawer and of course the C9.25 OTA) - should keep me busy for years, much to the other half's relief no doubt 🤭

Better multiply those 1000 up a bit more with all that 😅  That's a good idea adding a new step/piece of equipment each time.  You'll notice the difference and be able to concentrate on the new stuff, while understanding what's gone before.

If the lens of the scope looks clear, the dew strap could be doing its job - just wanted to raise it as a check point next time.

37 minutes ago, blameTECHIE said:

I checked my imaging settings and had changed the black level (I think this is offset) from 3 to 30 somehow, that's been put back, for now, set to 0.

Apologies, I should have gone into a bit more detail with the black point.  Offset is a setting within the camera - if you can leave this at it's default then it's probably best when starting out - it's usually a number above 0.  I'm not familiar with the Altair cameras regarding gain and offset, but any defaults offered - especially around "unity gain" are a good starting place.

The black point I mentioned is found within the post processing and refers to the histogram of the image.  At the left of the histogram is where all the data is, as it's stretched it can be tempting to pull the black level in to make the image dark and maybe hide some gradients we don't like.  The cost of this is potentially lost, faint data that's "clipped" and gone forever.

Here's an example histogram, with a gap to the left, giving some breathing room:

Here's the same histogram, but I've pulled the black point in.  New histogram at the top (clipped), the black point pulled in at the bottom but look at the number near "Shadows:" - That's the clipped pixel count, gone!  

 

You'll be able to see the histogram in GIMP too (this is PixInsight), but here's a quick example on the image above:

The blue looks clipped, the red and green just on the edge.  The colours in the image look OK, but the histogram suggests the channels aren't aligned.  

Of course, how dark we make the image is personal preference but if you can avoid losing that critical, faint data then try not to go too far.

Hope this helps.

 

Edited June 1, 2021 by geeklee

[Padraic M]

Hi @blameTECHIE not a bad shot at all for your first 'real' astrophoto! AP is a crazy hobby with so many parallel learning curves, and you really need to get some proficiency in them all to produce a result you might be happy to share!

For me, the best lesson was to keep it simple. You really have an excellent rig there with that mount, camera and scope. Keep the 9.25" and the OAG in the shed for the next few years! The filter drawer might be of use if you get a light pollution filter, and if you really want to add something to your current setup, the autofocuser would be really worthwhile. Manual focus is a real pain. Pop your Barlow in the bin - it's for visual, and it has no place in AP.

I'm wondering why you're using Sharpcap for capturing when you're using NINA for darks and flats? NINA is an exceptional piece of software for capture control and can do everything that you need. You can select your target, set up your framing, goto target with plate-solving, an excellent autofocus routine, a new sequence controller that is better than anything on the market, and fully integrated with PHD2 for guiding. It's well worth getting to know how to use it, it's not that difficult, and the support on their Discord channel is really fast.

Offset is different to the black point. With Offset to >0, your camera will add the offset level to every pixel. It reduces your overall dynamic range very very slightly, but it helps prevent you clipping your black point at later stages in processing. Many people will run with offset >0. Your camera manual may give recommended levels for offset and gain. (gain 400 sounds a bit high but I'm not familiar with your camera).

With Gimp, you need to learn how to apply levels and curves. I'm sure there are many YouTube videos explaining this - there are definitely many showing the same technique in Photoshop and the technique is similar. You're trying to draw out the dynamic levels that correspond only to your DSO (which are normally close to but not at 0), without also raising your background level or blowing out your highlights. You will start with an image and histogram that looks like this:

...and you want to end with a histogram and image like this:

Do this by iteratively pulling the midpoint (the middle, gray triangle) to the left to brighten the mid-tones, and pull the black point (black triangle) to the right, just so it almost meets the left-most tail of the histogram. If you move it too far to the right, you will clip your black pixels. Geeklee explains it well above. Hit OK, then go back in and do it again. Keep doing it until you feel that you either have a good, balanced image or you have bigger problems - as you adjust your levels, you will also bring out vignetting, contours, colour imbalances, bloated stars, bad noise etc. and you might need to divert to other techniques to sort those out. 

You want your final image to have a gray background, not black. It looks better and more natural, and also you don't lose information along the way. You can get finer control using curves, but I'll leave that for the advanced lesson.

[blameTECHIE]

A lot to take in there Lee but it is making sense - an enormous amount of help you've given me here, thank you and appreciate you taking the time to look in more detail at one of the screengrabs - I'm busted, I completely forgot to try and align the channels.  No excuses, just too keen to get an image - a lack of patience and I don't see any of that for sale on FLO.

And @iapa, thank you, I'd only thought about taking the darks for the exposure I was using, not building up the library with a view to referring back (DOH!).

..... hmm, PixInsight ...... I've got a book on that ....... 😉

NO! use what I've got, learn and then progress to the next thing!
(though that might be setting up the pier that has recently turned into a bird table because I've done nothing with it yet)

[blameTECHIE]

@Padraic M thank you - guilty there as well (and the histograms from yourself and @geeklee are really helpful) - I was aiming for a black background.

I knew there'd be a lot to learn after finally understanding the mount and guiding, but it is quite a step up when you finally have images to process.

As for NINA, well I knew I needed Darks and Flats to register in DSS, SharpCap seemed to take them (I know now what I did wrong) and produce just a master file for each which DSS didn't like (I should have just taken captures, and did last night).  NINA is brand new to me and I found the wizard in there for them, so tried to use that.

So many toolsets to do the same job - I really need to work on one and stick with it.  I like the interface for NINA, so maybe that's my task for the coming days/weeks (months/years ), sticking with the same target (where I know I get some results) and I'll have something to measure against for NINA and GiMP.  Hopefully results will improve and I can then take that experience onto new targets and challenges.

So thanks to everyone who has commented, I'll keep coming back to these comments to keep me on the right path.

Kev

[Padraic M]

I would recommend NINA or APT as your main capture tool - both excellent, and very little to separate them. NINA had the better autofocus until recently but APT now has an updated routine too.  SharpCap is useful for polar alignment.

Gimp/Photoshop is the hard way to process to be honest, but it is good to start there because you learn what's involved (and appreciate all the better what the other tools can do for you). You will move on to something more sophisticated when you know what you're doing. I've moved on to AstroPixelProcessor (APP - which replaces DSS and relegates Gimp to final tweaking) and will probably also add PixInsight shortly, but I'm not ready for it yet!

Whatever you choose, you will need to practice practice practice. AP takes lots of money but also takes lots of time!