rickwayne

ASIStudio worked reasonably well out of the box for me with live stacking, which is precisely what you want for this application. My concern is that the long focal length of your scope, coupled with the 120MC-S's tiny sensor, will yield such a small field of view that finding targets will be very challenging.

I've been looking at various options for transporting my OTA, so I'm not quite Neanderthal in this regard. Celestron make some nice padded soft cases for low-aspect-ratio items like SCT scopes. I've been looking at weather-resistant rigid toolboxes with wheels -- put most everything but the mount head and the counterweights in a padded box, I am thinking, which will help me keep things organized.

CEM70s are notoriously fiddly to mount on the tripod, so I have left mine mounted for over a year now and transported mount and tripod as a unit. I have not noticed any performance degradation. That's just one data point, and the prudent course is certainly to encase and pad the mount. CEM70s also have a means of locking the RA axis loosely in place with a bar through sets of holes in the housing and the RA axis, so they can be transported unclutched without RA flailing about.

What do your flats look like when you stretch them? Can you see any of the same artifacts? Personally I would not fash myself about it so long as it calibrates out. However you're having to manipulate in post to get rid of it, that's going to present a challenge when you image something with nebulosity filling most of the field. Moderate vignetting, in particular, bothers me little, since flats can eliminate it. General gradients, eh, APP and PI have good tools for that. Weird circle-things...ok, that's getting uncomfortable. I often work with linear data using a really hard preview stretch, to exacerbate problems like this so that they're easy to characterize.

As you doubtless have heard, the classic advice is to learn deep-sky with a telescope that demands as little attention as possible. A short-focal-length refractor is the optimum for that. Which short-focal-length refractor is probably going to matter less than you think it does. I mean, yeah, don't just nip down to a department store and buy the first Tasco you see, but an APO or doublet ED refractor from any reputable maker will be good enough. Sadly the Stellarvue SV70t is no longer a thing. I like this AstroBackyard rundown of good scopes for beginners; if memory serves, my Stellarvue was on that list when it was first published. I don't know what the prices are now though. Two things that really matter: Unless you plan to always crop to the center of the field of view, budget for a field flattener or flattener/reducer (or get a Petzval scope like some of the William Optics ones that don't need it). Sort of like "deep sky is all about the mount", astrographs are all about the focuser. Some people love Crayfords, having tried both I trust rack and pinion much more at the low end. If I had to choose between an achromat with a big, solid focuser and an APO with a piece of junk on the back end...I'd go with the former.

Probably not the same thing, but I saw this cross/"winged" pattern when the primary on my RC was way tilted. But mine was across the field. Aligning the primary fixed it.

It actually does work to just hold the camera up to the focuser and move it back and forth, too. Hard to precisely measure without an assistant, but precision isn't really necessary. But as Vlaiv says, you'd be surprised at how distant "infinity focus" is for a telescope. My experience with terrestrial photography led me to believe that eh, it's f/4 or so, everything from 100 feet away to infinity will be within the depth of field. Yeah, no. Not so true at longer focal lengths.

Actually my Astromania came spot-on. I was admittedly surprised.

Not a Newt owner, unfamiliar with the Concenter. But I can say that an inexpensive laser can be a big help -- won't do you any good for centering, but will get the tip/tilts correct. With a cheap one like that, you'll want to check the laser's collimation, but that can be done easily by perching it on an L-shaped support (pair of angle brackets, miter box, whatever), noting where the spot falls on a distant wall, and rotating it. If your mirror's index donut is in its optical center, you can repeatably ensure that your primary, secondary, and focuser are correctly aligned. AFAIK if the laser beam exits the focuser, hits the secondary, hits the center of the primary, bounces back up off the secondary and returns to its source, the focuser has to be at 90° to the primary and the secondary at 45° to both of them.

Sorry man.

Look up "hour angle" -- for a given RA, that will tell you when the mount will reach a particular position. Usually calculated for the meridian flips, but a horizontal counterweight bar is a horizontal counterweight bar.

If I look reeealy closely I can see a much fainter big circle on the flat corresponding to the lower-right problem. So perhaps not an orientation issue after all. You could run the numbers on the diameters of the circles to see how far the offending thing is from the sensor. I mean, if you find a chunk on the corresponding surface you've only fixed a symptom, but knowing where it's coming from could be instructive.

I use bias, not flat darks, with my 183. And with my LED tracing panel I wind up with sub-second exposures even at gain 53. Maybe they're too short but eh, it's good enough for me (check my Astrobin if you wonder if that's good enough for you. Not bragging -- just calibrating). I agree that it doesn't sound as if there's something wrong with your method. I'd be suspicious of the processing. Some notions I'd have to run down the problem: What exactly is the problem you're seeing when you process with these flats? Is the problem something you can examine by stretching a flat sub-exposure, or the integrated master flat? Do you have any of your old flats still lying around? Do they look similar when stretched? Other than the dust bunnies being all wrong, what happens if you swap them into your processing?

Easiest way to diagnose it is to rotate the camera a bit and look at the results. The image inspector in the free program ASTAP is the go-to tool for this.

Are you just using the 2600's built-in corrector? That would be frustrating, it's a nice feature but as I understand it you have to disassemble the train to adjust it. The GN corrector is adjusted from the side, which is absolutely brilliant: https://www.gerdneumann.net/english/astrofotografie-parts-astrophotography/ctu-camera-tilting-unit.html If you're not already aware of the free program ASTAP, it is a terrific tool for in-the-field corrections. Han has been making some changes and adding features in response to an active thread on Cloudy Nights, it's pretty amazing to watch. You may think of ASTAP as primarily a plate-solving tool but it has a LOT more going on. In particular, there is an "Image Inspection" tool which can render a tilt diagnosis quite rapidly from a starfield image. If you select the "triangle" rendering, you can orient the tool so that it corresponds to the adjustment bolts of your tilt plate and thus get pretty direct input. Here's a screencap from the discussion showing some of the output you can get from the inspector along with the image the numbers came from. This is a composite, mind -- it will only show one of these views at a time.

Unfortunately some time at the computer is pretty much the price of entry to this hobby. A single exposure of 40 seconds at ISO 3200 should easily show some MW nebulosity -- IF you hammer the contrast with levels or curves or some such. Try just yanking the contrast to ugly absurd levels in whatever processing program you favor -- I bet you will find all manner of tasty stars and nebulosity that a more finely- judged stretch will bring out nicely.

Unfortunately some time at the computer is pretty much the price of entry to this hobby. A single exposure of 40 seconds at ISO 3200 should easily show some MW nebulosity -- IF you hammer the contrast with levels or curves or some such. Try just yanking the contrast to ugly absurd levels in whatever processing program you favor -- I bet you will find all manner of tasty stars and nebulosity that a more finely- judged stretch will bring out nicely.

Downloading Stellarium or using Telescopius.com's virtual-scope view will help you decide, I think. I've been imaging for... whoa, can it possibly be ten years?... and still invariably start with Stellarium.

Well, you're no herd-follower, that's for sure. 🙂 I agree with you that much of The Dance is dispensable (e.g. guiding) if you're not to obsessive about IQ. Disagree about calibration frames, though. So much bang for the minimal buck there that it's hardly worth it without them. Mind you, I don't bother with darks for my DSLR, but that's because the results are measurably just as good. The thought of skipping cal frames for my ASI 183.....Hahahahahahahahahaha <snort> yeah, no. Good one, mate!

KStars/Ekos suite is what I use. I run it with StellarMate OS on a Raspberry Pi 4, but it can also run on Windows and Mac OS. It's a complete observatory-control system but you don't have to know all of it to use part of it. And it's all the same price (US$0.00). Well, technically I paid $50 for mine, which was prepackaged to go onto a MicroSD card so I could just download it, burn it to a card, and boot the Pi with it. But KStars and Ekos are free to download.

M42 is sort of a haiku of imaging -- anyone can put one together, but there is a great depth of subtlety and nuance available. You're well on your way! The brightest area in the nebula, known as the Trapezium, is easy to "blow out" so that it's undifferentiated white. And it's actually rather hard to not do that, while still getting enough exposure to swamp the noise in the dimmer regions. There is actually an enormous cloud of dust and gas around the frequently-seen parts of the nebula, so that's another axis of difficulty even for experienced imagers. Is the Trapezium blown white on your individual sub-exposures? If not, you may be able to retrieve some detail in it by masking it out as you stretch the contrast. In the past I've straight-up cheated by compositing with either a less-stretched version of the image, or an integration of much shorter sub-exposures, and masking in the bits with a soft brush in Photoshop. A 2- or 3-star alignment, as onikkinen says, will not do anything for tracking accuracy. What that does is ground-truth the mount's sky model so that when you tell it to do a GOTO, it will be much more accurate. But polar alignment is an entirely physical thing, hoicking the mount's polar axis around until it points exactly at the Celestial Pole. There are several packages now that can align to within a few arcminutes using your imaging scope and camera, by taking a series of images at different RA positions, plate solving them, and back-calculating the axis error that would produce them. And several of them don't need to see the northern sky at all, much less Polaris. You can also get a direct measurement of just how much DEC drift your alignment allows via the DARV method. Robert designed it as a means of actually polar aligning the scope via drift measurement, but it's also useful as a quick check. Basically you do a time exposure while (slowly) slewing the RA axis so that the image of the star reaches the edge of the frame in, say, two minutes, then slewing it back again. If you see a bright line, you're golden. If you see an elongated "V", you have DEC drift going on. He even thought of exposing for an extra interval at the start before beginning the slew, so one leg of the "V" ends in a bright dot -- that way you can tell which direction you're drifting.

I suspect it's common for beginners to underestimate the time and effort required to learn processing -- after all, most people contemplating DSO AP are already acquainted with terrestrial photography and pixel editors like Photoshop or The GIMP, how hard could it be? Hahahahahaha <snort>. Hard. I know that's what I thought, and my awakening was humbling. Very much like when (as an already-expert skier) I took up snowboarding. I mean (WHAM) I just take a bunch of images and (WHAM) put them in a stacking program and (WHAM) out comes my gallery-ready image, right? (WHAM. WHAM. WHAM.) The main difference was that the loud noises came from my head hitting the desk instead of the snow. Otherwise, a very similar learning experience. I'm a user, fan, and proponent of Astro Pixel Processor too, so I will acknowledge my bias right up front. But honestly it's the best money I've ever spent in DSO (well, after The Deep-Sky Imaging Primer). If I had to choose only two of the hard-earned lessons from my journey, they would be (1) Don't skimp on the calibration frames -- take and use them, and (2) It really does make a difference if you do as much of your manipulation on linear data, that is, data which have not yet been stretched. So gradient/light-pollution elimination, background neutralization, overall color balance, everything you can do before stretching, you should. DSS is great for stacking but reputedly not the best at the other processes. Siril is also free, multi-platform, and much more powerful. There are a bevy of other paid programs that each have their proponents, too. Most of them have free trials, so my advice would be to try out a few and see where you feel at home, then learn that program well.

Don't know to Skywaycher compatibility, but you can go to the INDI website and check if it's in the list of supported devices. Most people report no issues with hubs. I had some problems back when I was using a Pi 3 but haven't needed the hub for s long time. I use the Waveshare Motor HAT board plugged into my Pi, which directly drives stepper without using a USB port and is most definitely supported by INDI. It also lets you power your Pi with the same voltage and connector that most other astro stuff uses, so that cuts the cable clutter a bit too. I bodged a mount for the stepper and bought a timing belt and pulley. It simply drives the coarse knob on my Stellarvue.

I am famously bad at visualizing geometry, but if I understand you correctly, you haven't ruled out tilt in any part of your system. I take it that it's not possible to rotate just the camera, even just a little? That would be my first try. Next up would be an attempt to simplify the imaging train as much as possible -- eliminate the corrector and filters, and attach the camera as directly as possible to the telescope. Are all your connections threaded? What happens when you take the image train "as is" and point to different parts of the sky? Can you induce or change the tilt with gentle pressure on the camera? Is it possible to replace the camera alone with your laser? Do you have a "return to sender" collimator, so you can see if the beam bounces off the secondary, primary, secondary again, and back to its source? (And how did you align the cheap laser in the first place? I'd love to do that!)

Note that the rules of thumb were developed in the eyeball-guiding days. Since current software guides to sub-pixel resolution, you can be a lot more relaxed and still get good performance. However, do pay attention to the advice about mounting the guidescope. The amount of differential flexure that will lead to guide problems is absurdly tiny -- after all, we are talking about fractions of an arcsecond here.