Filroden

This is one area I've really struggled to get right. I've just emailed Bern at Modern Astronomy for a quote for a custom adaptor that should give me the correct back focus. This has not been helped because Skywatcher have changed the information in their manual. I used the one printed at the time I received my scope (about a year ago) which gives the distance as 61mm from the edge marking the start of the male thread on the field flattener. I've now just checked the latest manual and this has now changed to 66mm (so my email to Bern was completely wrong!). So 66mm is required. The flattener comes with an 11mm ring spacer that converts the M66 threaded flattener down to a M48 thread. So that gives a spacing distance from the back of the flattener including spacer of 55mm (close enough to the figure you've got of 54.9mm). So the way I figure it, you need to allow a little under 1mm for the filter (I think 1/3rd the filter width is the guidance but probably can be rounded to 1mm). Plus 6.5mm for the distance for the sensor inside the camera body and the 20.0mm for the EFW. (66.0mm - 11.0mm - 6.5mm - 20.0mm - 1.0mm) = 27.5 should be the space between the EFW and the M48 thread

I only image in LRGB and now in Ha. I've yet to take the next step and buy additional NB filters so I don't know if there is any SII signal.

60s was about my limit. The mount tracks well enough but anything above 60s and you can see rotation in the stars (oh, the problems of alt-az mounts). I originally captured the Rosette at 15s then went up to 30s and eventually a mix of 30s and 60s depending on filter. I can't go much higher than 30s with LRGB as the sky background becomes too bright and I lose all dynamic range. However, with the Ha, if the target was better positioned to the east I could probably have gone longer than 60s (field rotation is less a low altitudes and towards the east/west). I'd give 60s a try and you may even want to try 120s with your mount. It certainly saves pushing the gain.

This is a single 60s sub at 300 gain/50 offset and -20C on the Esprit. . And the result after I had to crop the stacking artefacts from field rotation (probably losing a good 10% around the borders which won't affect you).

I found the 400m frames the Rosette wonderfully. I have to crop mine back as I use an alt-az mount and I have to deal with field rotation, but with your set up I think it will show the nebula and capture some of the extensions that link it up to the Cone Nebula.

The Rosette is incredibly bright in red. I believe it has increasing amounts of OIII as you move towards its heart, so the colour goes from a purer red fringe, to a weaker red/orange as you move towards the centre. There are very few examples of emission/reflection nebula that show strong green/blue from OIII - the core of M42 being one of them. Given the short number of subs it's hard to tell too much about colour balance. However, my instinct tells me the colour balance is towards the cool/blue and probably needs to be be warmer/redder. As you say, 12 Mon is a K0 III star so should be yellow/orange in colour. When I enlarge your image, I can see this star does have a different colour to the other bright stars in the core but the blue cast is masking it at the moment. I'm sure once you've processed the big stack it will be much easier to process and work on the colour calibration. I find that once the basics fall into place (for me that's removing gradients and calibrating the colour) it becomes much easier to get a pleasing result.

Have you tried switching your balance for the other side of the meridian? What is causing the focus to change? Is it just chNgng temperature? As you say, your image suffers for noise because of the lack of subs but its unmistakably the Cone/Christmas Tree. The colours look so good with the modded camera! It fits the frame really well so a worthy target to try again another night without the focusing issues!

Grr, mine has done the opposite. Yesterday the forecast was for clear and winds weakening. Today it's now forecast for mist/low level clouds all day/night. I only managed 60 images last night and I think the last 30 might have been ruined by mist rising too. And I'm now in a permanent circle with my camera. I must have slightly ground one of the tablets and every time I open the chamber to blow the dust away, as soon as I close it, more dust appears. I think I will need to remove all four tablets, give the whole thing a good blowing over, dust the tablets down somewhere away from the camera and gingerly put it back together. The problem I have is any time I unscrew the EFW, it sometimes also unscrews the chamber which I think then disturbs the tablets This isn't usually a problem but I've been trying to improve my spacing so there has been lots of dismantling/rebuilding over the last few days. Good luck getting the rotation rig ready.

Sounds sensible. It also sounds like you have a plan at least, so once you've rested it should hopefully work. I'm managing to add a little data to my Rosette Nebula. My first attempt on Tuesday was ok, but I didn't get a lot of data and the Ha dominated the LRGB by some margin!

I think we're taking the "size isn't everything" to extremes! Guess we could call it the cone nebula?

Wow, those images are high contrast! I feel like someone stretched my eyes until I could see into UV and IR!!

Thanks Ian. I think it helps that there is so little background in the narrowband. It cuts through light pollution, etc like butter, so what little I have (about 40 mins) is much easier to stretch than the equivalent L data. There is a definite point on the histogram where it transitions from black into signal. When I process L data I have to cut into the data a little (possibly clipping up to 2,000 pixels or less than 0.001% of the total data) but I can get a darker background clipping no or only a handful of pixels with the Ha data. I have so little RGB (less than the Ha for each channel) and it's weaker (see comment above about having to remove backgrounds/stretch/clip). There was enough to colour the stars which I'm pleased with. The star size comes from the Ha data, which gives beautifully small stars (ignoring my eggy stars in the corners) but it's actually taken colour from the RGB data. I think I need a lot more RGB and I need to push it harder. If I get time I may reprocess the colour again and take the RGB data into Photoshop where I can boost it harder without affecting star colours. I might also try reducing the contribution of the Ha into the red channel. I think because I've used the Ha for the luminance and it dominates the colour, they have matched 1:1, giving that flat feel. My plan now is to relocate my scope to the other end of the garden so I can avoid the neighbour's steam vent and gain an extra hour or so before the target goes behind the house. I would like to add to the Ha (maybe 80 more minutes) so I can get more from the background, but I need to match that with at least an hour each for RGB - more than I can achieve in a single night so I may have to collect the data in chunks of 20 minutes per channel. It also means getting a power extension cable and moving the laptop outside (which then means I have to follow it) Anyway, for now I'm going to resist reprocessing today as there forecast suggests a chance of some clear skies over the next couple of days. Instead, I have 15 mins of Ha data on M81/82 that I didn't use and which shows some extensions in M82. I foolishly didn't read the tutorial enough and in my eagerness to process something yesterday, I took my LRGB non-linear too quickly before blending the Ha and then I got impatient to move onto the Rosette data!

Thank you! Under an hour of imaging and about six hours of processing But it's now my favourite image that I've taken though I'm torn between the mono and colour versions.

And here's 15 minutes of LRGB data on M81/82:

Though presumably you could set these manually in the meantime so you don't lose any clear nights?

The Spyder software has me adjust the settings on the TV. So I had to adjust the LED Backlight setting (much brighter). It then went on to calibrate colours and adjusted the driver which turned the image a very warm red so I reset it. I've now deleted the adjusted profile and reset my TV settings back to default. I need to start again! Anyway, here's a new version of the Mono Ha image. I found my problem - it was sat between the keyboard and the chair! I had changed a setting in Photoshop which meant I was applying a different correction to the one I though. Much happier with this one. This has had background removed, initial noise reduction on the background, levels stretch, more noise reduction in the background, sharpening and some localised contrast enhancement. I then moved into Lightroom and added a little more clarity and adjusted the black and white points. And here's my attempt at a colour version. This uses the above Ha image for luminance (I discarded my other luminance data as it made the image noticeably worse) combined with colour data using a blend of R + Ha, G & B. I now understand the comment that Ha images can take on a salmon pink colour! I did try a HaRGB without adding the Ha into the R colour channel but it also didn't look as nice. And for comparison, here's the Rosette Nebula I processed using the earlier data (i.e. not including last night's data).

I think I'm narrowing down my problem moving from PixInsight to Photoshop. The exported TIFF is being brightened to extremes and using curves to bring it back is causing my noise to shoot up and losing the natural transition. I need to check my setting as I think it's related to the image being mono.

The main thing that is bugging me is the harsh graduation from background to nebula in the second version. I think I might have pushed the processing too hard as the Ha image in my colour version is nowhere near as stark.

NGC2239 in Ha Skywatcher Esprit 80, ZWO ASI1600MM-C and Astrodon Ha filter -20C, 300 gain and 50 offset Integration of 35 x 30s and 22 x 60s and processed in Pixinsight and Photoshop Version 1: uncalibrated, no background removal, no noise reduction and just a simple histogram stretch using levels and curves Version 2: calibrated with bias, darks and flats, background removal, noise reduction, histogram stretch using levels and curves, further noise reduction, localised histogram balancing to enhance dark structure In all honesty, the first version is so much better for not having me process it! I have no idea what I've done differently this time compared to my earlier images, but I just can't control the background in this.

It is. It's got a lovely field of view with it's 400mm focal length and it's a very solid scope with a great focuser. I have the matching field flattener too (not that you'd notice given how badly tilted/spaced my imaging system is at the moment).

I have something odd going on and it may be a result of calibrating my TV with the Spyder. I process a mono image and export it to a TIFF. When I open it in Photoshop it's like the exposure has been cranked up 2 or 3 stops undoing all my lovely noise reduction!

That's good progress!

My ZWO ASI1600MM-C

NGC2239 - initial integration These 6 images (a screenshot of my Pixinsight workspace) shows the results of initial calibration, alignment and integration. They have been auto-stretched by Pixinsight. Starting clockwise from the top left corner: H_mono: integration of 35 x 30s and 22 x 60s, aligned with the first Ha image in the set R: integration of 33 x 15s and 10 x 30s, aligned to an L image L: integration of 77 x 15s and 9 x 30s, aligned to an L image H: integration of 35 x 30s and 22 x 60s, aligned to an L image G: integration of 39 x 15s and 10 x 30s, aligned to an L image B: integration of 30 x 15s and 10 x 30s, aligned to an L image The last five images will need a lot of cropping as the images were collected on two nights over quite a time span and have therefore suffered a lot of rotation. I created the first image so I could create as wide a field for a mono Ha image. Perhaps unfairly, the Ha images really stand out. I think this is for two reasons: I collected more data, the narrowness of the filter means the image has less background signal so it can be auto-stretched harder by Pixinsight (the histogram between the Ha and L is radically different, with the Ha data being confined to a tight peak). I think I will have to synthesise a super L from the L, R, G and B data and even then, I think I will be throwing the L away and using just the Ha data. I just hope the colour data doesn't add too much noise!