rickwayne

After four hours of work, I had 14 minutes of Ha data on the Pelican and Ha, with no guiding to speak of. The result should have totally sucked, but it sucks only a bit! Yay?

Time to make yourself an Astrobin account, I think! Even if I include all the landscape stuff I was doing before I got into deep-sky, I only have about 16 images I'd show to other people. And that's over much more than a year.

As someone who often agonizes about this kind of thing, I note that if you miss one night of imaging because you can't decide, you're already likely behind the curve of total satisfaction over time. You can't go very far wrong with these choices, right? Otherwise it wouldn't be hard to decide.

The consensus seems to be that practically speaking, unless money is no object CMOS wins out over CCD these days. 12-bit readouts aren't as much of a limitation as you might think, at least not if you're stacking. There's a current discussion going over at the CN beginning/intermediate forum that's mostly on point for that, Jon Rista notes: The main benefit of 14 or 16 bits over 12 bits is that the gain at which quantization error becomes effectively meaningless is lower. Lower gains have more dynamic range, and thus you can potentially better-utilize the DR the sensor hardware has to offer with higher bit depths. With lower bit depth cameras, we can recover DR by stacking more subs. With lower read noise, we can use shorter exposures than with higher read noise, and since lower bit depths and lower read noise generally come in pairs, bit depth in practice (assuming you are processing in 32-bit float or higher precision), need not be a primary concern. A 12-bit camera might not be the best choice if you want to acquire very long exposures and stack only a few subs...but if you are stacking 90 subs or more, I would not really be concerned about bit depth.

Ooo, we're 183 Buddies! Although you've got total snobbery rights with a Baader Ha filter there, instead of my measly ZWO. I hope you just enjoy the heck out of the thing. I really like the smaller pixels that let me crop more aggressively without making my images look like Minecraft screenshots.

You go Paul! Think of me while you're enjoying your clear skies, and may your brain run at full speed. Meanwhile, in Wisconsin...

Two things: 1) I think I have posted here before about the visual astronomer I met in Texas who defined an imager as "a guy swearing in the dark at something that isn't working". 2) The more time I spend in this hobby, the more it reminds me of aviation. Intellectually challenging, expensive, full of moving parts that all have to work but frequently don't, leaving you debugging complex systems in the moment. And between that frisson of fear that never went away even after thousands of hours, and hypoxia (I'm asthmatic, The Stupids come on pretty fast for me with altitude), I always felt as if I were operating well below peak cognitive capacity. So too with imaging. Late hours, in the dark, feeling rushed to fix things fast before the precious imaging time slips away. I am constantly gobsmacked the next morning by how stupid I was the night before. (OK, yes, many people are frequently stunned by how stupid I was the night before, let's just move on now, shall we?) One crutch does help for both of them: Checklists. Oddly enough, I never seem to actually use mine in the field. Should remember my mindfulness classes, slow down, and make use of what brain cells I do have. PS: My last time I was working myself up into a fine lather over why the 183 just wasn't producing enough stars to focus on. Yep, lens cap. I didn't even have the excuse of an interruption.

Oh. My. Your maturity and restraint serve as a model to us all. EBay, nothing, I would have been more like "It's all going ON THE MOON" and started hurling things. I can't say I haven't had KStars and Ekos roll over and die on me. But at least on the Mac it's uncommon. On the Pi...maybe once every other imaging session. If I'm checking it, no huhu, I just miss a bit of imaging time till I get it back up. If not...lunar astronomy. I am saying.

Oh, sorry Carole! I just formed an assumption based on your text and the screen shot. Never mind! Siril is definitely worth a look. It has its quirks, and has misbehaved occasionally for me and for some friends, but it's my go-to among the free programs for stacking. Multiplatform, open source, reasonably performant. User interface takes a bit of getting used to and it does leave intermediate files on your disk with the gay abandon of a bunny fertilizing your yard. Calibration, registration, stacking, and (L)RGB composition are pretty straightforward (in addition to the registration it does among the subs in a stack, it also automatically registers your L, R, G, and B frames.) Demosaicing Bayer-gridded frames is a bit nonobvious, easy enough once you get it. Wow, is that a ringing endorsement or what?

Wow, I'm envious. You figured that out while you were still shooting? >;-}

Well, me implying that someone else plays up saturation or contrast for dramatic effect would DEFINITELY be a case of stones thrown from glass houses. By a black pot, at a kettle. Etc., etc.. I like 'em dramatic and while I might blush at my own shamelessness from time to time, I make no apologies. If an image pleases you, it's doing what it's supposed to do, IMHO.

And if you want a simpler life you can go with so-called "bicolor" imaging, with just the two brightest wavelengths (for emission nebulae, H-alpha and O-III). Some folks create a synthetic green channel by mixing the H-alpha and O-III, some just let its bicolor freak flag fly. There is an excellent reference on Cloudy Nights on initial settings for the ASI 183: https://www.cloudynights.com/topic/616524-sub-exposure-tables-for-the-zwo-asi183mm-and-qhy183m-and-colour-versions/. If you're running with just a light-pollution filter, use the "Broadband" category. Don't sweat the sky-brightness criteria too much, you'll probably wind up changing from that initial exposure anyway. This is just a recommended starting point. Oh, and flats: Unless you're some sort of luck genius, the filter sitting so close to the imaging sensor is just a haven for little dust motes. I never appreciated the ultrasonic cleaning feature of my DSLR so much until I had to live without it. The point about sensor proximity is that the shadows' circles of confusion are actually small enough to be visible when you stretch the image (unlike those of dust on the objective lens). You won't see it in an unstretched sub-exposure, but my stretched subs often look as if my imaging train has come down with measles. So you want to shoot flats. Calibrates right out. 🙂 PS: Speaking of registering R/G/B or H-a/O-III/whatever: Siril also does a pretty decent job there. I'm super-impressed that carastro can get Photoshop to work for that, in my experience it sucks at that task. Seriously, I will never even bother trying PS for that purpose ever again. Astro Pixel Processor is absolutely outstanding.

You've definitely got it going on there! I confess to pixel-peeping and saw what I would have thought was chromatic aberration if it had been a refractor. Look at some of the very brightest, biggest stars -- there's a sort of turquoise "shadow" cast toward the center of the image. ??? There seems to be a bit of a cast of the same color in the heart of the cluster itself, green is not a color I'd expect to see there but what do I know. Coma? Does coma come with a color cast? Sorry, my ignorance is showing yet again.

I don't think you'll be sorry. The 183 demands a slightly higher game than, say, the 1600, but I can't say enough good things about mine. You probably always already process with darks, but you will never process again without them, tell you that for free -- the amp glow on the thing is pretty stark. When you look at your first light and scream "AAAAA, WHO'S SHINING FLASHLIGHTS ON THE SIDE OF MY SENSOR?!!" just breathe and repeat The 183 Mantra: It calibrates out. It calibrates out. It calibrates out. But you certainly do want darks at exactly that gain, temp, and exposure!

Heh. Yeah, I think that's OK with us. Going to be a beaut! Is there enough H-alpha to make that worthwhile to collect that while the moon is glowering at us?

Well, that is annoying. Normally "they" say don't bother binning your main camera unless it's a CCD, it just cuts down the number of pixels without any improvement to signal/noise. But here cutting down the pixel count is exactly what we want! Downsampling should produce a similar result, but offloading the binning to the camera (if that worked) would necessitate less CPU time downsampling, in addition to speeding up the image download. That's a pretty annoying hit.

Nice thing about M101 is that it comes pretty close to the zenith (though I'm at 42° N), minimizing light pollution and atmospheric issues.

Note that the 183 comes with a filter holder -- at least mine did! -- that threads into the interior of the adapter rings, so that you can mount a 1.25" filter without going out and buying anything else. I didn't think I'd be very happy with black and white imaging but I've been pretty happy with some of the stuff I've been able to pull off in my (red zone) back yard with a 183MM and the ZWO Ha filter. (Yes, it's RIck's Horse again. What can I say, it's my favorite image so far. 🙂 )

I find that platesolving works quite well for my guide camera on the Pi, not so much for the main (20 MP) one. I have had it work, mind, but it's slow and doesn't always solve. Five things: In some cases the lack of index files will only slow solving, rather than kill it, as the software has to search for its image within larger footprints rather than find it quickly within smaller ones. Do ensure that the astrometry index files are actually in the correct place. Try selecting your guide camera and solving with that. The smaller image should make it more palatable to the Pi, and will serve as a smoke-test. Depending on how well your guide and main scopes are collimated, it might even be all you really, truly need. Check the command-line parameters that Ekos is passing to astrometry. In mine, I have it downsampling 16x. Are you seeing reasonably focused stars in the images it's trying to solve? Poor focus can make it spin endlessly (go on, ask me how I know...) I have to say that, having tried it with the Pi and with a 2018 Retina MacBook Pro, one of those things is a lot less frustrating than the other. But one of them will run all night on about seven electrons, and the other gives me maybe two hours of imaging and it's Tango Uniform Mode Time.

Re sub length: IIRC Sara is doing her (absolutely gorgeous, I go to your site every time my Envy Level drops and I need a refresh) imaging from very dark skies, so her narrowband subs will be much longer than we wee mortals'. ?

Y'know, sensor size is not in itself an advantage. You want to match your desired FOV to the sensor size, yes, but angular pixel size is also in play. I deliberately chose a smaller sensor for my first dedicated astro camera precisely so that smaller objects would more nearly fill the frame, while the smaller pixels helped address the undersampling that my DSLR rig gives me. Smaller-pixel sensors are often noisier than bigger-pixel ones, true, but between today's sensors and stacking, that's a lot less of a problem than it used to be.