ONIKKINEN

Your tilt measures 10%, which is basically nothing at all. Off axis aberration is also around 10% which is very good. My advice would be to leave it as it is and enjoy a working telescope and not try and mix something that is not clearly broken. The right side has barely perceptible tilt that blurXterminator would definitely get rid of completely. Alternatively binning or resampling a little bit would probably hide that too.

Yes it should scale the histogram correctly now. You should be looking at a roughly 8000 median value for a mid level exposure at 14-bit.

NINA is displaying a 16-bit histogram here for some reason, whereas your image is presumably taken with a 14-bit camera. The max value in a 14-bit camera is 16384, or 16383 if we include 0 as one of the values so fully saturated. You need to go to the Options->Equipment-> and under the Camera tab set your Bit depth to the correct value which would be 14. This should make the flats wizard work too if there was a problem with determining a nice exposure because of the incorrect assumed bit depth of the camera.

I reached the same conclusion as @AstroMuni above, calibration with this set of frames works as it should. Below a false colour rendering at an extreme stretch: As we can see the image is very flat, apart from the sky gradient but this is unrelated to the issue. No ring artifact to be seen. What you describe with the focuser tensioning and such is exactly what makes the ring thing happen, because at one camera orientation gravity will act on the imaging train differently than in another. You could test the stability of your whole system though, and its fairly easy to do so. To do that, take a flat with the telescope horizontal to the east, take another with the scope horizontal to the west, then one to the zenith one to the south and north etc. Point is to get a flat in as many imaging train orientations as possible here. Then do a simple pixelmath division between any of the 2 flats (flat east / flat west for example), what you should get is a uniform gray mess with no clear gradient or any features to be seen. If you see a gradient or any features other than noise, you have a mechanical problem. This method reveals the smallest issues with your mechanical problems in the scope, give it a try?

The initial thought i had in mind is a flats calibration issue, since this kind of ring artifact happens when your light frames and flat frames do not mechanically match (because for example focuser tilt/sag, unreliable collimation, image train stability issues between the lights and the flats). You did mention you have thought of calibration issues but this is still my guess. I used to have an unreliable focuser and an unreliably thin aluminum tube in my newtonian, and most of the time flats had this kind of ring artifact which went away after making sure everything is mechanically sound. Any ideas that come to mind are just wild guesses without seeing the raw data though. Can you post a raw light, a matching dark frame, darkflat frame (or bias, whichever you use) and a matching flat frame in raw format straight of the camera? You can attach .fits (or any other) files here on SGL just by dragging and dropping them below where you write a comment so no need to link something to an external file hosting site.

Phenomenal first image and actually not just as a first image - the image is good in general, really good job. Learning all of PixInsight and the various xT suites for a first image is very impressive.

Wow! That's a lot of dust. Top shelf processing too, really a winner image right here.

I think you are being a bit unfair here. There is nothing wrong with sharpcap itself and just advicing to "take some images with it" is just plain silly when OP has a genuine worry here. I would imagine manufacturers also measure camera performance using exposures and measuring the pixel values within (like sharpcap does). These technical specs cant be seen in a single sub frame, at least easily so i really dont think looking at a subframe has any meaningful value here. But the small technical differences can be measured and they can have a real effect in integrations you would not have been able to otherwise see. Im sure you know all this... Definitely not a panic over nothing. However @zernikepolynomial if you look at your graph and the published graph they do look similar in many parts. Sharpcap has skipped gain 125 and gone directly from 100 to 150 which is a problem if you wanted to know what the stats are for gain 125 but im not sure there is a way to force sharpcap to use specific gain values for the graph. Both 100 and 150 look like fairly accurate measurements compared to the published values so i think it may be possible the read noise drop actually does happen at 125 but its just not shown. The actual amount of read noise is slightly higher, which i think is a bit concerning but it doesn't look too bad. The "low read noise" modes are something i dont really trust myself. My Rising Cam branded IMX571 camera has a low read noise mode, but there is no documentation on what this actually means. I do notice that the framerate drops exactly by half when this is engaged, leading me to think that this is some sort of double exposure internal dark calibration thing, which would not be useful at all for long exposure imaging where this probably gets disengaged. This would not be apparent with sharpcap measurements since the exposures used are very short hence my distrust for it. If we assume your camera is not using the "LRN" mode (whatever that is), then at gain 150 you only have a discrepancy of 1.49 to 1.417 which is not too much. Still a bummer that its more than it should.

The histogram 1/3rd of the way rule is just a guideline, but it doesn't actually mean anything and cant be used to gauge whether an exposure is good enough if you want to be pedantic about it. After all you could double your ISO and get a much brighter histogram which surely is much better? Well, not necessarily and often DSLRs have a point of diminishing returns at some ISO after which read noise no longer decreases linearly (not sure about the 400D, some searching suggests ISO 400). If you really wanted to do the math you would need to know the electrons to ADUs conversion ratio at the chosen ISO value, the amount of read noise in electrons and some other technical gibberish. These values are not given by DSLR manufacturers so there wont be an easy way to do all this, hence the common tip of histogram 1/3rd of the way through as an indication of a good enough exposure (its not, but better than nothing or taking 1s frames). For what its worth the 60s exposure you have linked here looks ok to my eyes. Maybe a little bit on the dark and noisy side, you could try exposing for 2 or even 3 minutes if your guiding can handle the extra length. If not, take a few hundred subs like this and there should be a nice M27 in the end. Not familiar with APT, but if its just a visualization thing then it doesn't matter. If it actually applies some kind of stretch to the raw data and saves it modified then leave it off.

Sure has been a weirdly clear and warm summer so far. Lets hope it continues well into September once the dark skies return. Probably not, but cant complain at the moment.

I drive around 45-60min to a bortle 4 location when i go imaging so often there is no choice to let my 8" scope cool down properly. I help the process along by driving there with the heater off so that the scope cools down by the time i arrive and i lose as little time as possible to settling tube currents. Really makes me question the sanity of the whole hobby when its -10 or colder for the drive there... And often the first 30-60min is troubled with thermals anyway. Running a primary mirror fan helps a lot though.

Actually i mixed up something too, i thought you wrote refractor, but it was a reflector . Anyway with a newtonian your coma corrector will most likely be the weakest link in terms of what kind of resolution you get out of the thing (coupled with seeing of course, but this you cant help really).

You can bin the 183MM images to get a more reasonable sampling, either x2 or x3. Hardly a point in changing a camera especially since the 174MM has a smaller sensor than your current one. And by the way, its not really possible to just say that one is oversampled and one is undersampled without knowing the aperture of the scope, the quality of the used flattener/corrector, the typical seeing conditions and so on. But for almost all imagers out there a sampling of 0.75" per pixel is severely oversampled (you got over and undersampling mixed up here, a small arcsec/pix value is typically oversampled not undersampled). Bin x2 with the 183MM might be ideal, or very close to ideal depending on what exact scope the 650mm fl refractor is and what kind of seeing you typically get. If not, bin x3 to 2.25'' is still very good and would consider it "high resolution" if the data supports this resolution.

Here is an astrophotography example of a severely undersampled image: And then a closeup at 500% zoom: The smallest stars, the ones that are actually only one pixel look somewhat blocky at 500% zoom but none of this was visible at 100% because they appear like point sources. None of the more than a single pixel sized stars appear blocky. In short, dont worry about undersampling, which may not even occur.

First, welcome to SGL! With my 550D and an f/4.4 newtonian coma corrected to f/4.2 i used to see the same thing, a noticeable dark band on one of the flat sides of the sensor. Used to think its the mirror casting a shadow as it rises out of the way, or shutter shadow because of the mechanical shutter. But if you look closely at your sensor you see that the sensor is very boxed in deep in to the sensor recess. The camera body/mirror mechanism at one side of the sensor is close enough that it could cast a shadow (like the part circled below). In that case there is nothing to do about it, except of course keep taking flats and accept the lower SNR on one side. Usually you can anticipate this and compose your shot so that there is nothing of interest on that side. Other than that, you probably have a normal sky gradient in the image which could be confused to something originating from the camera. It could be a coincidence that the sky had a gradient that matches the sensor orientation in this case leading you on a wild goose chase.

I ran a very quick process (in Siril) to the stack: Looks like star colours are alive and well, so at least its not a capture issue where stars were saturated to begin with. So its all fixable it seems. Stars are bi-colour because of the filter passing only the blue-green O3 and the very deep red Ha. Personally for this reason i would work on the stars-only layer in Photoshop and manually fiddle with the levels until the starcolours are the most natural to my eyes, but this one isn't too far off either so not strictly necessary. What i did: Bin x3 (average), Slight crop, background extraction (crude, could have done a better job), Photometric colour calibration followed by a manual white reference on that bright-ish white looking star in the top left corner just because i thought it might take the edge out of the very red stars. Stretched first with an Asinh stretch at 300 power and then a simple histogram transformation. Where you probably took a wrong turn would be the hyperbolic stretches, especially if you ran it on the stars-only image. I recommend first processing the image to the point where stars look good to your eyes and only then separating them with starnet. Then keep working on the starless layer until you like what you see and re-introduce the stars. This way the star layer needs minimal work because they were good before you separated them. I usually do all this in Photoshop because its much easier to see what is going on with the layer system. But typically the stars only layer sees only minimal work with maybe some saturation or levels adjustments, but definitely no hyperbolic stretching at that point.

Would you be willing to share the raw stacked file, or just a single subexposure? It would be easier to give advice with the raw data at hand. But anyway, how are you stretching the data here? You shouldn't drop the white point below the point of star saturation, and it looks like that may have happened considering that every star here is just white and colourless. Its also easy to destroy star cores if you use one of the more advanced hyperbolic stretch tools and place some of the sliders somewhere other than the best spot, personally i dont like using them too much. If you ran deconvolution you may have also destroyed the stars if it was ran too aggressively. The image looks fairly noisy so i would recommend not running that in this case.

I think you hit the nail on the head here with the ASIAIR. Its a very effective business strategy, although not very consumer friendly. Hook people in with a well priced ASIAIR + 120MM guider combo and swim in the profits later when that consumer upgrades to the 2600. The guide chip on the new duo camera is the same as in the new-ish 220MM. I have the 220MM in an OAG and its been very good. Have imaged through an Antlia Triband RGB filter with 3x approx 30nm passes and OAG guiding is no trouble at all at f/5. Typically guidestar SNR is at least 100, but could be as much as 1000. So safe to assume a tighter filter would be at least workable if not good since the SNR really doesnt need to be so large for guiding.

I stick small setscrews/grubscrews on a piece of tape and write on the other side where i took them out of (and fold so that they dont fall). The AZ-EQ6 is full of these concrete soluble size screws that look similar but can be slightly different sizes and there is no chance i would remember where they should go after a few weeks. The magnetic tray thing sounds like a good investment, less MacGyver anyway.

Magnification for imaging purposes is not useful at all, and actually more questions arise when you think about it a bit more. Lets say you view the image on a smartphone at arms length, what is the magnification now? What about a 50'' TV, surely the magnification is larger now that the image is larger? Or if you crop the image to only half its size, is the magnification now doubled? As you can see for imaging purposes where the size of the image can and will change in the end a "magnification at capture" thing is misleading and mostly useless. But we can use a better metering stick for something similar: The resolution of your scope/camera combo which in this case is 0.76'' per pixel. Unfortunately the 183 has tiny pixels so you are already at a disadvantage here, but you can bin the image later of course. Just as a coincidence i image at a resolution of 0.76'' per pixel, with a premium 8'' newtonian and a very good coma corrector (that costs twice the astromaster 130 alone). Furthermore unfortunately 95% of the times i am significantly over sampled, and the remaining 5% i am just mostly over sampled so i would say the likelihood of your astromaster/183 combo being a good match for galaxy imaging is 0. Probably looking at binning to x4 or further to get a not-soft looking image at 100% viewing. (which i think is a decent metric of how an image performs, if the image is soft at 100% there are too many pixels to show the information. Its all subjective though so many will disagree on what is appropriate) There are more problems with the scope however. The focuser is one of them, being entirely plastic and 1.25'' in size. Meaning there are no coma correctors that you can easily fit to it. And even if you could fit one in, will it work? After all a coma corrector is designed to fix coma that comes from a parabolic mirror, but if the mirror is spherical then it would not fix the aberrations that come with it. Without a corrector you are limited to using the central 5mm (at best) of the sensor to get a somewhat sharp image. No reason to give up though since you already have the scope. Try it out under the stars, maybe yours has a better mirror and is not entirely soft? Then you could think about fitting a more suitable focuser and maybe a coma corrector too and maybe it does turn out to be a decent scope. However if you dont already have a 2 inch focuser you could slot into it you would need to buy one, which will probably cost more than the scope. And at this point you could just skip the headache and get a 130PDS.

You can stack all of the data to one image with Siril (many others too probably. What you'll need to do is calibrate the datasets with their own calibration frames first and then move on with stacking. Choose a reference frame (best image of either set) and load that as the first image in Siril. This will make it the reference frame and during registration the image scale from this image is automatically applied to any other image you load. For example you choose a 102ed image as the reference frame, the 72ed data is then upscaled to the 102ed data. Or vice versa of course. Then just stack all of the images together. However even if you can stack the images does not mean it all goes flawlessly without weighting the subs. The bigger scope will provide loads more signal to noise ratio than the smaller one, so stacking both datasets together without any weighting will result in an image that may be worse than just the bigger scope data alone. Which is why you should choose the "weighted fwhm" option in weighting for stacking. This will calculate weights based on star counts and star sizes, both being slightly worse in the 72ed will give that data a lower weight overall but probably still contribute to the image somewhat. I think you can run 2 instances of NINA in the case when you do dual camera imaging, although have only read about that briefly so wont throw any more guesses on how that goes really.

My Astromaster 130 gets outresolved by a half-achromat 90mm refractor in planetary/lunar visual use so i would imagine a very spherical mirror in mine considering the not insignificant difference in aperture and that my refractor is not exactly top of the line stuff itself. Seems like there are varying quality copies of the scope sold and sometimes you read an account where the scope is not too bad in someone else's eyes. Probably why Celestron does not advertise anything specific about the mirror if there is a lot of variation between mirrors.

Global cooling seems like the least of our worries for the climate and Earth in general. Even if we reversed our direction of greenhouse gas generation and went too far any kind of glaciation event will be seen centuries in advance. Easy to pump the greenhouse gases back into the atmosphere in that case. Whereas global warming is not centuries away, its right now and everywhere. But i do agree 4 million is an afternoon project and a 1 square meter unfolding prototype on a rideshared falcon 9 with an orbital lifespan of 2 weeks. 4 trillion would maybe start the project going properly. Probably not something that will see any real results in the following few decades at least.

Mini-PC scopeside to which you connect to via wi-fi or a wired lan connection from your home computer/remote desktop? This way you keep all the important cables short and let the scopeside mini-PC do all the work. The ASIAIR is kind of the same, but you permanently lock yourself out from non ZWO cameras and other equipment. You are also stuck with the software it has. Since you mentioned wanting to have room to grow the mini-PC option ticks more boxes for sure.

I think you can use any 12V DC power supply as long as its rated for at least 3A output. So 5A would be more than good enough. I have a power in/out readout screen in my 12V power bank, so the guess of 1 amp in use comes from that. Its not super accurate, but its not far off either.