ONIKKINEN

To me it looks like atmospheric dispersion is playing a not insignificant role in the elongation of your stars. Blues and reds are on the opposite side, as they refract through the atmosphere at different rates and so can land a few pixels apart on your sensor. How high was Leo when shooting? I find this issue just about perceptible at somewhere around 50 degrees and increasingly distracting at lower altitudes. Anything lower than 40 and i find colour channel alignment after stacking a necessity rather than a bonus. Im not a refractor owner myself so couldnt tell if chromatic aberration from the optics could separate colours like this but the atmosphere definitely will.

Decreasing light pollution as the night progresses, or the target getting higher in the sky, probably both. Some street lights are dimmed in the AM hours of the day, or even shut down. I notice that some patches of highway around here have only every second light on at the lowest traffic hours of the night. Some folks might also have their yard lights off for the night. Most businesses shut down lights at least partially at some point of the night and car traffic producing extra lights is at its minimum. All of these are small effects but it adds up and there can be a real noticeable difference in light pollution in the weird hours of the night. But usually this isn't a shocking difference, but maybe a 10% reduction overall. Did you check your secondary mirror for dew? Or a coma corrector lens (probably the tube facing one) if you have one. A thin film of dew can be difficult to spot without shining a light directly on it so it might just seem like there was no dew but really there was. I sometimes got dew on my secondary before i started using a dew shield, which then made the problem go away even for the worst nights.

Great detail in the core and everywhere else, beautiful image! I do agree with cajen2 with the greens though. Try running SCNR (green noise removal) to fix it? Tried it in SiriL and seems to fix the green cast very nicely.

Also, forgot a simple method of testing the flats. Just look at your calibrated frames from all over the session. All of them should have their flats applied the same way, but if some of them have the donut or some other problem in them and some dont you will know that some subs were in a different collimation (due to anything, focuser, mirror etcetc) than the flats.

Yes, you do need darks even if the camera is low noise. Its a pretty clear cut case, examples below: First calibrated without darks: Then calibrated with your bias frames as darks (and bias frames): Now the problem isn't completely gone as i can still see the outline of the 100% illumination zone as the darkened area, because you really would need to use darks to make this work properly. Another issues to keep in mind would be more mechanical rather than data handling. Did you move the camera before taking the flats? Did the scope sit in sunlight and warm up? Many things can happen with newtonians that ruin flats because the primary mirror can move in the bottom. Thermal differences between night and sunlight could probably also deform the tube enough to take you out of collimation. Flats being offcenter and showing this kind of weird center pattern could be due to that, miscollimation because of either the mirror cell itself being sloppy or the tube deforming, or the focuser being sloppy or really anything. I would try to take flats at night in the middle of the session to make sure they are the best they can be. You can test whether your scope has some mechanical issues by taking one set of flats at the beginning of the session, one in the middle and one in the end. The tube will be in different orientations and so mechanical issues will manifest themselves to the flats. If you see these issues, you need to fix the root problem before flats will ever work consistently. But you can take darks now and see if it fixes, or makes the issue better (it will). The mechanical thing is somewhat of an eternal migraine for newtonian users, myself included, but think of that later.

What does a single flat frame and the flat master look like? Did you use all calibration frames? You have over correction, which to me looks like you might have skipped darks or bias, or both. Depending on the camera and flats exposure time you may need to use darkflats to calibrate the flats too. If you used one of the newer low thermal noise cameras then bias works just fine for that (i do this, no issues). This image does look like the skyflats had some gradient to them with one corner much better than the other, but the over correction is what bothers me most.

What does a single sub look like? Difficult to tell if you have just stretched it to this point or if it was like this in the subs. But i am going to guess that there is no way 120s on M51 would be overexposed. Its a bright object for a DSO, but its not really bright enough for you to accidentally saturate pixels with it.

Looks pretty good to me. Sharp galaxies and nice detail even if the background is a bit noisy, but i dont think it detracts from the image. If you want to denoise the background, the best way would probably be to just shoot more subs as its not a super long integration yet? I shoot at a similar resolution as you, but with 5x the aperture area as your scope (assuming its the FSQ85?) and still think that my background is weak at this kind of integration time, so must be with your scope as well. Maybe it looks worse because there is a lot of background in this image and with nebula images there isn't nearly as much?

I know what you mean, running on camera batteries is so stressful. I had 4 old and dubious quality batteries with my 550D and if it was very cold outside that got me just 2 hours of subs, of which most were junk due to many reasons so there was always a sense of urgency with getting things going quickly. There are dummy batteries that insert one end to the camera and the other to 12v DC or mains power if you want to run cabled and not worry about batteries. Most astro vendors have these, including FLO of course.

Does look a bit like some napoleonic era field artillery piece with the mount hidden like this.

Is the star trail drift in RA or DEC? Very important to know. DEC drift would be polar alignment, while RA would not. Below is a graph of my AZ-EQ6 running under guiding assistant in PHD2 with guiding disabled. This was around 15 minutes of observation. Blue is RA, red is DEC. The jittery motion is due to mechanical issues within my telescope and the way my 60mm guidescope is mounted rather than actual jittery motion of the mount itself (although some of it is probably that too). The sharpest cliffs in blue here are happening in around 20 seconds and span across several arcseconds, so if you expose at this part of the worm, the exposure will be a guaranteed failure. Other parts are less severe and its possible you just by chance land on a part of the period where you see no issues for 60s. The worm in my mount isn't particularly good because of its aggressive features, but you could have something like this too, no way to know without measuring. This is no issue at all when guiding however, all of these are "slow" and predictable enough that guiding takes care of it completely. Maybe the sharp cliff shown here can have an extra 0.1'' RMS error during an exposure there, but its not a deal breaker. As for the handset PA, i think you have it as good as it can be with that method. If your stars land centered each time and the mount sees no reason to adjust, it means it cant do better than you already tried.

Is that a DIY cooler? Looks interesting. If you can make the DIY cooler work at consistent temperatures night after night, you can take one set of darks, biases and dark flats and use those for every session and dont need to take them each night. If your flats exposure time is very short you can get away with not using dark flats and instead just use bias to calibrate the flats. If its maybe not so controllable you could take several sets of calibration frames at different temperatures and then use whichever set is closest to the actual imaging temperature that night. Flats will have to be taken in the exact condition the optics were in when imaging, so before you remove the camera from the scope and each night with their own flats. If you can leave the setup as is each night and dont take anything apart, its possible your flats will work just fine reused but i would take them every time. Using a light panel of some kind is the simplest method, but since you have 50mm of aperture you can use a decent sized phone screen, tablet or laptop screen as a light source for the flats. and so probably dont need an extra tool for this. Very quick to take and so not much in the way of excuses to not do this each time you're out. As for the multi session thing, you need to calibrate your session with matching calibration frames. So if you can take a library of darks, bias (and dark flats, if bothered) at matching temperatures where they can be reused indefinitely, the only calibration frame that is session sensitive would be the flats. Once you have calibrated the subs well it doesn't matter from which session it was anymore and you can stack any number of them together without issue and disregarding the session it was from. If you dont want to go through the trouble of storing calibrated frames you can use DeepSkyStacker with the "groups" function to drop each session to their own group. This feature calibrates each set with their own calibration frames and then stacks everything together in the end.

M82 has a significant starburst thing going on that is bright in Ha so its not a bad choice for that, or the many emission regions within M81. But to capture the galaxy itself, especially M81 since its face-on towards us would be faster without the filter. Starlight will still radiate in OIII and Ha even though they do not "emit" in it like nebulae so filter or not there will be a picture in the end.

My mantra on galaxy imaging is that broadband filters have too many negatives to be of any decent use and i dont see how one would be useful, unless in awful conditions (Bortle 8 maybe). Firstly, real colour results are off the table, because a large part of the spectrum is blocked. Expect everything to look blue with most broadband filters. With CLS filters you get green results as most of the reds are gone. Second, blocking light pollution also blocks the galaxy itself. Starlight is mostly the same colour as sunlight, which is what artificial lighting tries to emulate, and light from galaxies is almost entirely starlight with a speck of emission here and there in actively starforming galaxies. So by blocking the part of the spectrum where light pollution is most intense, you also block the brightest* part of the galaxy. * Depends on the galaxy partly. Very active spiral galaxies like M33 are noticeably bluer than most other galaxies, so the negatives are less apparent while still there.

Looks like a type 3 USB B connector (printer cable, as it was called before type3) to me.

+1 vote for ditching the bahtinov mask. I started comparing bahtinov mask focus to just HFR reading focus with NINA a while back and found that star HFR can often be improved by as much as a whole pixel even when focus seemed perfect with the mask. Now that im used to it i get consistently up to 30% better focus by just looking at the reported star HFR values compared to a mask.

Bird or insect maybe? Or perhaps some asymmetric piece of space junk/space rock that "skips" off the atmosphere and so changes direction. I really dont think its a satellite as its doing an inclination change burn as this kind of change would need ~10km/s delta v to make in low earth orbit. If it was in higher orbit, we would see only a part of this trail as it would travel much slower. 10km/s is not really something that any satellite or other spacecraft for that matter is going to have available to it. Its even worse when you think about the time this exposure spans, which is probably just a few minutes. So a very short burn and 10km/s delta v = not happening. Very strange.

Steady drift to one direction is probably drift in declination due to poor polar alignment. Actually doesnt even have to be that poor if the session is long and you did not recenter. I found it necessary to babysit the mount and check the framing from time to time when i shot unguided. Periodic error is back and forth where the tracking speed of your mount underperforms and overperforms periodically over one worm period (480s) but shouldnt result in steady drift for longer than one worm cycle. This motion is only in RA. By the way doing the 3 star alignment will tell you how much youre off in polar alignment in the end, so you could use that to check how accurate it was. This does rely on you being very accurate when centering the alignment stars. It would make GO-TOs more accurate too, but not help with tracking accuracy.

Looking great for first tries with short integration! Guiding is what will make your EQM35 work much more reliably, although still wont do miracles for you. My unit had a particularly nasty periodic error so unguided was not a good way to spend clear nights for me. You can try and test how much periodic error you have by polar aligning as well as you can, orienting the camera so that RA is level left to right and shooting an exposure of at least 480s towards a low declination part of the sky. The image will be ruined of course but then you can measure how much periodic error you have by measuring the length of the trails in RA. Wont work if its windy though as the mount doesnt like that. When you get this measurement you can make an educated guess as to how long could you shoot unguided. I would guess that 15s is already close to the max exposure time that is somewhat reliable, so you could just use that.

I dont doubt that visual astronony is in decline due to light pollution increasing globally and most people cant easily access the quality skies needed for the best views. But i dont think visual is dying, or actually will probably ever die because it is enjoyable even through poor skies. It just takes an attitude and expectation shift for the viewer to understand that some views will not be happening under LP. I find visual very satisfying whenever i convince myself to leave the camera at home even if the views are somewhat disappointing. I think representation online plays a part on this perception of visual being on the way out too. Most of the time i dont feel like writing what i observed on a short session, but images i take will one day end up online. The process of taking and handling the images also sparks discussion far easier than observing IMO. I am maybe 90% imaging and 10% visual, but i dont think ill ever drop the visual side to 0.

+1 vote for the Rising cam IMX571. Its a bit more expensive than the altair 294 but the newer tech is worth it IMO. If calibration issues worry you, you dont have those problems with the 571 based cameras (mostly). Also true for the 533 by the way. I would also urge you to forget about the higher resolution estimates given by astronomy.tools and focus on getting closer to the lower estimates so 2" per pixel or more. Dont forget that binning allows you to change shooting resolution at will (by multiples of original resolution). From several thousand subs i have shot so far most are oversampled at 1.84" per pixel where i work and i can safely say none of them come close to 1" resolution in real detail and that is with a 200mm aperture.

🧐

The AZ-EQ6 guides fairly well, considering it was pointing my scope towards a tree 🤣: I was really scratching my head on what went wrong and why the mount was suddenly acting up, especially in declination which really had not moved much for the entire night (1arcmin PA). Checked all kinds of cable snags and whether the tripod had sunk in to the icy surface it was planted on and only then saw that the scope was pointing to a forest in the way. I had for some reason not thought of the target moving to the other side of the sky during the night, which of course it did and this location is against a forest on the west side. Not sure what i learned from this, other than PHD2 does not have forest-compensating features.

Catching some moon and high cloud beaten photons from NGC4236 at the moment, as im curious how well these conditions compare to already existing 5h+ i captured some months ago under much better conditions. Awful skies now but better than nothing i say!

I have attached some hose clamps i think made for AC tubing to tension the tube and hopefully improve rigidity, like i am pretty sure @Captain Scarlet did to his 8'' (cant remember whether it was the VX). I also drilled some holes through the existing tube clamps and fit a Skywatcher vixen dovetail i had lying around on it to act as a top rail to tie the tube rings together. I lack the critical astronomy resource known as a local window frame supplier 🤣 so this will have to do for now, but looks like these fixes while ugly have improved the mechanics of the tube quite a bit. Trying to squeeze or lightly punch the tube with a laser in the focuser reveals that it doesn't move nearly as much as it used to be so you are correct this operation did not in fact cost a fortune. The springs and silicone thing im not worried about (yet). It looks like the VX mirror cell already uses this method, seeing as there are 9 (or is it 6? Not sure) small blobs of silicone between the mirror and the cell itself. I dont have the cell out right now but last i checked there was enough clearance between the clips and the mirror to slide something like a credit card in without much resistance. Not sure why the clips are still in place though if its already been glued. Precaution by design perhaps? Poking this silicone reveals that it is glued to both the mirror and the cell and not just something thats in between the 2. The springs themselves are also very strong and it takes considerable force to move the collimation nuts, so much that its actually a bit annoying. Im sure it still can be rattled around in transportation but during session, i dont think so.