rickwayne

Heartily concur that a computer for acquisition is a real force multiplier. Plate solving obviates searching for targets. Quantitative focusing metrics, even absent robotic drive for the focus, means fewer tossed subs and getting to "go" more quickly. Analyzing your images in real time for focus, star eccentricity, proper exposure, and more lets you deal with problems as they arise and so saves oodles of wasted time. Autoguiding, of course, as well as automated dithering as you point out. All these things can be done without a computer driving the scope and camera, of course, but it's just that much more effort and fiddle-faddle. Not gonna argue with the choice of Pi and Astroberry, since I chose essentially the same system! (I bought StellarMate OS because it was simpler than AB back then, but same same.) I should note that an update to KStars sometime in the past year or two includes a Bahtinov focusing metric, so you can slap on the mask and look at numbers instead of squinting at spikes and trying to decide if it's really centered.)

The nebulosity around the Pleiades is so much dimmer than the stars themselves that it takes a lot more integration time to bring it out. You could do it with single exposures, but you'd run into trailing problems and really severely blown-out and bloated stars by then. All our deep-sky work is trickery with dynamic range and contrast, compressing the tonal range at the high end and vastly expanding it at the low. As an exercise in learning the ropes for acquisition, single frames are a fine idea. But I wouldn't spend a lot of time trying to get good-looking results of much that way. (Maybe you could do star clusters if you got the exposure just right.) This is one of the topics very ably covered by Bracken, Lodriguss, Richards, and those folks in their books. Basically a single image is one sample from a rather low-level, noisy signal. Say two adjacent pixels are slightly different in tone "in actuality" (i.e., the "real" values we never know, but can only approximate). But your sensor, over one minute, happens to record 83 photons for one and 83 photons for the other during your one exposure. Now forever after there's no way even in principle to discriminate those shades, and when you dramatically increase the contrast by e.g. 10X, those pixels stay the same shade even though they should get more and more different as you stretch (increase the low-end contrast). But if you take a hundred samples (83, 85, 83...), you might discover when you average them that Pixel A is really 83.6 photons per minute while Pixel B was 82.4. Now the contrast-enhancement has something to get its teeth into, and some detail emerges that the single exposure could never show. Of course, multiplying the exposure time by a hundred has the same effect on the math. But exposures that long are usually impractical for the reasons noted above.

You should be going left to right in the PHD buttons, right? First "Connect" (the USB symbol), then "Loop" (the circling arrows), then "Auto-select star" (the star, obviously), then "Guide" (the green-background crosshair). Unless PHD has already been successfully run, it should begin to do a calibration when you click the green Guide button. Basically it issues successive pulses to the mount to displace the image of the star and measures what happens. First it does it in one axis (DEC, I think), then pulses back to the starting point, then does the same thing with the other axis. This lets it map a given pulse length along each axis to the resulting star displacement so that it knows how big a correction to issue when you're guiding and it sees the star move. During the process you'll see status messages like "North step 2" or "Nudge south", the other axis of course will say things like "East step" or "West step", and it should end with "Guiding". Obviously that didn't happen for you! The star-cross test is similar, but is more of a diagnostic (it's under the "Tools" menu). It's a simpler operation since it isn't really trying to keep track of the star, it just issues a bunch of pulses to try and draw an "X" with the star. I don't know anything about APT, so I don't know what kind of toxic interactions might be occurring. I see a "Guide" button there though, could it be fighting with PHD over who gets to issue the guide pulses? I would check the APT docs about that. I know that my suite (KStars/Ekos) has a built-in guider or you can optionally use PHD. Maybe you don't have to run PHD at all? You did not say specifically but APT is successfully slewing your mount to the target, right? That at least rules out one set of cabling and driver issues. Note that for guiding with PHD, the best practice is to pick a star within a few degrees of the meridian's intersection with the celestial equator, and let it do its calibration on that first. If your mount can talk to the computer and tell it where it's pointing (sure looks as if yours does), PHD can then adjust the pulse lengths for other parts of the sky. The other really good thing to do is, once you've run your calibration and slewed to your target, go to the Tools menu and select the Guiding Assistant, start that, and let it run for two or three minutes. That will analyze all sorts of useful things and recommend an optimal range for guide exposure, suggest any parameter changes (and make them for you if you like), etc., all tailored to your target's part of the sky.

Did PHD calibrate? Can you do a star-cross test?

Depending on what software you settle on for running the scope and acquiring data, you might want to figure out plate solving sooner rather than later. For newer versions of the stuff I use (KStars/Ekos) it's pretty much pushbutton out of the box, and you would not BELIEVE how much less frustrating imaging can be when you can select a target on the computer and say "go to that", and the gear happily cycles through taking a frame, analyzing where it's pointing, slewing the scope, rinse and repeat until your target is centered to within a minute of arc. The old salts will say that you should learn the sky until you can do it manually, but life's too short and good imaging nights too rare. Admittedly if it busts for an evening I'm pretty well out of business, but that's awfully rare. I've lost way more imaging time to not being able to FIND THE FRICKIN' TARGET.

Shockingly good results for such a Charlie-Foxtrot first night. My guideline is that if smoke doesn't come out of any of your equipment at any point, it counts as a win. (Yes, I have, and yes it did, and yes, iOptron was really good about replacing the burnt bits.) Checklist. Speaking as an aviator who survived twenty-plus years of, er, me...checklists be your friend, dude. Helps to set up in daylight and run through everything possible while you're NOT freezing in the dark, too.

See also: https://www.macobservatory.com/blog/2020/7/30/the-growing-list-of-mac-planetary-imaging-and-processing-applications

Of course the knee-jerk answer to noise is always "more integration time", but you knew that. You can quantitatively analyze your images to see what might be most economically improved. Noise? Faster optics, as you say, or longer total integration time. Detail? Have a look at the full-width half-maximum numbers for the stars in your images, and their eccentricity. That will tell you if focusing aids, better optics, or more attention to polar alignment and/or autoguiding might pay off the best. It also pays to be aware of your image scale -- how much of the sky is represented by each pixel. My K5-iis DSLR, for example, is somewhat undersampled for my Stellarvue, meaning that the pixels are a little too big for optimal detail. That's one reason I selected the ASI183, which has much smaller pixels. Good primer and calculator for that here. I guess you could say I've had success with 30-second unguided NB exposures with a mono camera (guiding wasn't working that evening). No APOD, but it's recognizable. This is on a CEM25P mount which has a factory guarantee of +/- 10" periodic error or less, at 362mm F/L and F/5 or thereabouts.

<SFX: HOLLOW LAUGHTER>HAHAHAHAHAHAHAHA HOHOHOHOHOHOHOHO! Oh, you sweet summer child. Y'know, I said something very similar about $3000 ago. Soon to be $5500, I'm ordering a CEM70...

Can you provide a little more detail on what you're doing? What software? How are you using it? Are you sure that your focusing is correct? If you can get planets, you ought to be able to get stars too, they're just dimmer. You may have some trouble achieving what you want in deep-sky work with that gear, however. Your mount is designed for visual work, not for long exposures, and the 120MC-S's sensor is pretty small. Bright objects (M42, M31) will be way too large to fit in frame, and most smaller ones will likely be quite dim. The scope is also f/9, so that necessitates long exposures. If you can get it to focus, you might do better with your Nikon's larger sensor. Not trying to discourage you, just trying to set your expectations. There is a reason the deep-sky big dogs have those really expensive mounts, and it isn't just bragging rights! I would counsel one of two options: Either do planetary stuff while you save up for a mount that's twice your budget, or pick up a camera tracker (e.g. SkyGuider or SkyTracker) and do your deep-sky work with a "prime" (non-zoom) telephoto lens on your DSLRs. You can pick up an old used manual-everything one, which will cut down on the expense -- autofocus and diaphragm do you no good in astro anyway!

A secondary consideration, if you're imaging on an equatorial mount, is aligning with the mount axes. If you know that e.g. horizontal in the image is right ascension and vertical is declination, it's a lot easier to diagnose problems.

The classic advice is "go long on mount, skimp or delay on optics or camera if you have to", as you may have heard. Your budget would accommodate an EQ6-R Pro or even an iOptron CEM40. If the former, you could add a nice old manual-everything prime telephoto in the 3-400mm range from the used market. That would obviate adapters and field flattener or flattener/reducer needed for a telescope. Next step after that could be autoguiding, then a scope. There are many, many excellent targets amenable to that focal range. 600mm is actually a tad on the long side if you're starting out with "serious" deep-sky AP, and f/7 is pretty slow. So you'd want a flattener/reducer anyway, putting you right about...400mm. An upgraded mount like that would be no harder to operate (well, the EQ6-R is a beast to lug around, they say), but deliver significantly better performance and would not need to be replaced for years, maybe never. Just my two cents. Did I do it that way? No. Scope Fever had me in its implacable grip. Do I wish I had? Yeah, kinda. But that Stellarvue sure is a jewel... 🙂

What dissatisfies you with what you're producing now? That would inform any practice, gear, or software recommendations I could make. Trailed stars e.g. leads to different advice than noisy images.

Ahh, missed that your Mac wasn't a laptop. I've been doing software development on MacBook Pros since 2013, so I just assume. A laptop is a really good idea even if it's mostly for processing, it's good to have a big screen handy to examine a frame, etc. Of course if your Mac has more snort it still might be the processing platform of choice -- no reason the computer you use in the field and the one you process on have to be the same. I am a big fan of the little-headless-computer-at-the-scope model. ASI did a pretty nice job with theirs and people seem to like them. Do double-check that it is compatible with your kit, they are a bit notorious for playing nicely only with ASI gear. You may have gathered by now that astronomers strenuously advocate whatever bizarre bits of gear they personally have managed to decipher, so apply a bias factor here. BUT: I find that you can have a reasonably seamless experience with less money spent and vastly more capability by going with one of the Linux options, either the StellarMate gadget (includes a Raspberry Pi like the ASIAir, turnkey experience), buying your own Pi, case, and StellarMate OS (around US$120), or buy your own Pi and case and install the free Astroberry server which gives you essentially the same software. Like the ASIAir, there are mobile apps which you can use to run the widgetry. But you can also remote in from a laptop, desktop, tablet, or phone and use the Pi as a computer in its own right, which I find incredibly helpful. The open-source gear-driver software common to these, INDI, supports just about every piece of astronomical and photographic gear you can think of, including odd bits like weather stations and observatory domes.

You realize you are the ONLY astronomer ever who would characterize a session as a "bit of a comedy of errors", right? My criterion for success is a bit like the pilot's "any landing you can walk away from" -- any session where I don't actually cause my gear to emit smoke, or have to pick up equipment off the concrete, counts as a success. (TBF, as pilots my wife and I did try for a higher standard than "did not crash this time".) And iOptron were amazingly tactful about replacing the burnt bits inside my CEM25P, I have to say. If I may be so bold as to offer suggestions: Write (and rewrite, and re-re-rewrite) a checklist. I'd offer you one but of course gear varies, and so does what different astronomers consider "obvious". The exercise itself will help you more than the piece of paper anyway. BIG lesson from aviation. It has been eight years and I can still recite our Cardinal's pre-engine-start checklist from memory -- but we still used the paper copy every single time. Plan the flight, fly the plan. Go through the moves you'll make in advance, try to think it through. Take your time in the field. I always feel pressured not to waste precious dark-sky time, but it takes a lot longer to reshoot. Again like aviation, or rock climbing if you prefer. Anywhere your body or gear goes, your mind should have already gone. If the dark and late hour have you thinking slowly, it's OK to move still more slowly. See if you can find a magic zone for your alt-az locks -- enough not to slip, but not so tight that you can't overcome it. If you're unfamiliar with red-dot sights for shooting, their huge advantage is that you needn't align your eye and peer through them. You can keep both eyes open looking at the entire starfield, and move and tighten the ballhead so that the dot moves into the right spot in your field of vision. You can buy one with a little machined-aluminum widget that mounts it on your camera's flash shoe for US$30 from Amazon. Try "Astromania red dot sight flash shoe" in your favorite shopping search engine. This saved me thousands of dollars, in that otherwise I'd have been hurling expensive gear into ravines and setting even more fire to it. You mention shooting at a very high ISO, and then cite 100. ????? Actually it's a brilliant idea to set the ISO at 6 bazillion or so -- I don't remember, maybe Canons can do eight or nine -- for quick snaps to get the framing right. Then your checklist will remind you -- right? -- to set it back to the imaging ISO of 400 or 800 or whatever you use. Until you get an intervalometer, a remote, or computer control, your camera's self-timer will work amazingly well. You are in luck that IMO the very best software for stacking and processing runs on Mac OS, Windows, and Linux. Those would be: SiriL (far and away the most powerful free solution) Astro Pixel Processor -- what I use, full-featured and IMO the single best solution for beginners PixInsight -- legendarily powerful, with an equally legendary cliff-like learning curve There are plenty of other packages which all have their adherents. I would not recommend anything other than APP to someone just starting out. Finally, as you may have noticed, this little avocation has a few non-intuitive quirks and complexities (in the sense of "Donald Trump and Boris Johnson have a few personality flaws"). While you can learn it by ramming into each one and solving it in turn, your head will probably thank you for a subtler approach. Jerry Lodriguss has several good books for beginning astrophotographers including ones specializing in DSLRs. Charlie Bracken wrote my favorite all-rounder, The Deep Sky Imaging Primer, and Steve Richards' Making Every Photon Count is reputedly quite good. If you equip yourself with the well-rounded knowledge these authors can impart, you'll have a solid framework into which you can slot your ongoing learning. Welcome, and I salute your courage! There's a lot to learn, which is what makes this so endlessly fascinating. Well, that and the flashy cars and girls.

I can't say I've got it down to a science, but 30-40 seconds is what I've been using.

N=1 dataset: I routinely use the ZWO filter wheel and the guide cam connected to the 183's hub, with the stock supplied cables. Although the EAF is doubtless pulling more current than the EFW.

Is that direction aligned with either axis? If you're not guiding, the mount shouldn't be running the DEC motor at all, so consistent drift along the DEC axis just about has to be due to polar alignment. You can use PHD on stars on the celestial equator, one on the meridian and one near the horizon, and run the Guiding Assistant tool for a few minutes to check. That will quantitate things and give you a decent estimate of your polar alignment error. If it's aligned with the RA axis...huh. Wrong tracking rate selected (e.g. lunar)? Do your PHD guide graphs show any particular pattern?

You're using a one-shot color camera, right? You could always shoot unfiltered and debayer into separate R, G, and B channels, then do star reduction independently on them. Or figure out which way to move the focuser and by about how much for each of the three channels, shoot three sets, and keep only the optimized channel from each. Or put yourself together a poor man's RGB setup with red, green, and blue filters, focus independently for each, and do the same with that. That's essentially what I do for stars with a mono cam, my only advantage is the lack of a Bayer filter slowing things down. Even better if you're using starnet++ or something to do your stretching on a starless image so you don't try to overlay color on bloated stars. The great thing about doing separate exposures for stars is that they're so nice and bright, with a high SNR. So it doesn't take very much extra time to get good data, and obv. very little stretching is needed.

Even if you prefer to stick with ST-4 for guiding, it's worth at least setting up a test with pulse guiding (as the others have recommended) to isolate the problem further. What do you mean that it won't step east when you're tracking w/o your guide scope? What would ever issue a "step east" command?

Since you're imaging at f/5 or higher, the bandpass is not going to have a big impact on you. Since these are interference filters, they're rather sensitive to the angle of incidence, and faster optics produce a broader light cone whose edges impact at a more acute angle. I use 7-nm ZWO "new" filters, and I do OK. Baader and Optolong are somewhere between roughly equivalent to a step up, depending on who you talk to. Astrodons and Chromas are the spendy ones. Not sure how where Astronomik fits. Something I hear over and over again is that OIII filters are particularly prone to bright stars forming halos, so if you want to splurge on one filter, that's the one. Search for "OIII halo bright stars" to find discussions and examples. You may find that some manufacturers claim that their filters are parfocal, i.e. you don't have to refocus when switching. I wouldn't count on that too completely, critical focus often requires refocus on switch.

So, really great for narrowband, is what you're saying! Gotta say, alacant, those look reeeally nice. I don't even mind the spikes so much, though I agree a circular mask would be a great addition.

This turns out not to work well in practice, at least for deep-sky objects. Such a multiplier (usually "Barlow" in astro) spreads the light cone out for more magnification, so that less impacts the sensor. A 2X Barlow effectively adds an "f-stop" to the scope, converting an f/4 into an f/5.6, a 5.6 into an 8, and so on. In fact many -- maybe even most -- deep-sky heads do precisely the opposite, mounting a focal reducer that concentrates more of the image circle on a smaller area. Brighter, but less magnification.

RIght? When I think of all the futzing about I did in the KStars planetarium view...oh well.

Not sure how you're planning to mount the camera; what weight problem would arise that wouldn't if your camera is mounted on a tripod? A 135 shouldn't be any issue. You might find it difficult to get the scope off and the camera on without budging something, but 135mm is a pretty forgiving focal length. You didn't mention the make/model of mount. If your scope mounts with a Vixen or Losmandy dovetail, it's simple to get one that has holes to allow a suitable-length 1/4"-20 screw into the tripod socket to bolt the camera down onto it. E.g. this from our beloved sponsor. The other option, if your scope is attached with mounting rings, is to just piggyback your camera on that. Less fuss in the dark.