rickwayne

Definitely shoot bias (or flat darks, if you prefer) and flats. Darks for DSLRs are not divinely ordained -- some need them, some do not. My Pentax's sensor has so little dark current at cool ambient temperatures that darks actually impair the image. Not saying you DON'T need them for your camera, just that you should experiment and see. Flats IMO are must-have, and you need either bias or flat darks to calibrate with those (the latter are just darks that you shoot at the same settings/exposure as the flats). As for stacking: while the math for averaging pixel values works out the same whether you stack each session and then stack the integrations or do one massive stack of all sessions' frames, many other things do not. In particular, rejection algorithms for outlier values (satellites, airplanes, cosmic rays), as well as background normalization, are statistical and work much better for larger data sets. If you're just doing simple averaging then no, it doesn't matter.

No, I can't.

Well, one reason to use bias instead of flat darks is that you don't have to redo them if you change your flat exposure. By the same token, my Ha flats' exposure differs significantly from my luminance. For me it would be four sets of dark flats (Ha, OIII, L, RGB) but only one bias. I'm sure that plenty of people get by just fine without worrying about it, just as there are many who reuse flats for many nights' imaging.

The lush options are: ASIAir Pro Pegasus PowerBox Mount with built-in cable management (i.e. iOptron CEM70) The less-spendy options are: On-scope computer (e.g. Raspberry Pi) Powered USB hub mounted to scope Spiral wrap, split flexible conduit, etc. Mega-twist ties to gather and subdue the cables Contrary data point to tomato, it is not necessary for a cable to snag in order to produce deleterious effects. I've got the guiding data to prove it, at least for my overloaded CEM-25P mount. When I let the USB and cooler-power cables hang off the camera on the end of the scope, my guiding was always frustrating. When I used a foot-long, rubber-coated wire tie to bind the cables to the scope or dovetail in line with the DEC axis, and then (with a measured amount of slack) to the mount or tripod, things got measurably better. One of the reasons I bought a CEM70 was to wave buh-bye to those rituals. Of course now I've added an autofocuser that uses a bespoke cable, not USB, so I still have dangly ganglia. Well, I'll run that cable up through the DEC axis any day now, the mount is built so you can do that.

WRT to PixInsight over Photoshop: Oh, yes, absolutely. If you wanted a complex part made out of plastic, you could certainly whittle it with an X-Acto knife, and you probably wouldn't have to study up to do it. However, investing the time in learning to run a 3D printer is going to yield a better product with less fuss. However I am going to make a pitch for Astro Pixel Processor here. Much easier to learn, according to people whose opinion I respect, and for many of us it has all the needed tools.

Welp, I'll put my oar in the water. Stellarvue SV70t-IS, ASI183MM Pro, ZWO filters, iOptron CEM70. Frames (all at gain 65, -10℃): B: 15x30" (7' 30") B: 37x40" (24' 40") G: 15x30" (7' 30") G: 45x40" (30') L: 32x30" (16') L: 81x40" (54') R: 15x30" (7' 30") R: 45x40" (30') Total integration time: 2h 57' 10". Processed with Astro Pixel Processor and Photoshop.

> Anyways, thanks for advice, I love this site, why is everyone here so friendly? Right? Overall there seem to be fewer jerks in astro forums than in many other Internet places. I use Pentax DSLRs and so hang out on the Pentax astro forum and it's the same way: Friendly, supportive, never a spiteful word, and people seem eager to deploy their expertise to teach you without any attitude.

You've gotten some pretty good advice here. Good astro gear has to be made to incredibly precise tolerances -- the critical focus zone for my little refractor is less than 100 microns thick, and I have to track to better than a second of arc (i.e., less than a millionth of a circle). And the market is tiny compared to other activities, so economies of scale are hard to achieve. A lot of beginners think you need a telescope first thing to do astrophotography, when that's really the last thing. Until you have solid equipment and know how to use it, magnification is your foe, not your friend. An old telephoto prime picked up cheaply on the used market will do you quite well, a 50 is even easier, and a wider lens easier still. You don't need autofocus, you don't need auto-aperture, and you don't need a long focal length. Google "barn door tracker" if you're reasonably handy -- you can build one pretty cheaply and they can work for exposures in the tens of seconds for shorter focal lengths. You can learn the game of focusing, polar alignment if applicable, and most especially processing, whose complexity and difficulty many folks with photography experience completely underestimate. Note that for an APS-C sensor, it's more like a rule of 300 than a rule of 500, but it depends on your tolerance for star trails. And really that's the lesson for the whole thing: Learn what your equipment is capable of, and work within those limitations. This was shot two weeks ago with a very sophisticated mount: A plastic crate that I balanced the camera on. It's a nine-year-old DLSR. 20-second exposures, and a wide-angle lens, obviate trailing. This was shot the same night, it looks like a telescopic view but it's actually a 50mm lens on another DSLR (in fact you can make out a piece of the second image's field of view in the first image if you know where to look). $2500 equatorial mount with autoguiding let me do a variety of exposures from 15 seconds to 10 minutes. But I might have gotten a very similar result with lots of short exposures with a much less sophisticated mount, and/or a higher ISO. There are a lot of great deep-sky targets large and bright enough to image without the spendy gear. And working with them will teach you a ton about the science and techniques. Welcome!

"Backfocus", as it's customarily used, is an annoyingly misleading term. When referring to the required distance between a flattener and the sensor (the most common use of the term), it actually has nothing whatever to do with focus! Our telescope optics produce a curved field by their nature. So a flattener is used to ensure that the stars in the corners are in focus at the same time as the ones in the center. But the flattener works at a specific distance -- if you move the sensor closer or farther away, the corner bits will be distorted. That spec is what's commonly referred to as "backfocus" and is fixed for a given setup. E.g., flatteners often have a distance of 55mm because most DSLRs with a T-thread adapter happen to measure 55mm from the sensor plane to the front of the adapter. So think of the flattener-to-sensor part of the train as one unit, usually the distance is maintained by some sort of spacer. In the case of the DSLR and a 55mm BF flattener, the adapter is all you need; other cameras might require extension tubes, and there are some which are adjustable. Usually fixed tubes are preferable because they can't creep out of spec. That whole unit moves in and out to achieve focus, depending on the distance to the target and the temperature (which affects the length of the tube and other components). As Clarkey notes, focusing during daylight probably won't produce optimal nighttime focus, not least because the temperature will almost certainly differ. The depth of the zone of critical focus depends on your particular setup, but it's probably in the 100-micron range (mine is 74 microns). A 1℃ change will easily change the length of your optical path by that much. So: Establish the correct "backfocus" to spec*, then with that locked in, find a rough focus point during the day if you like, but always finish up just before imaging with a Bahtinov mask. And in fact, as the night progresses, best practice is to refocus every so often as the scope cools. I use one hour but your mileage may vary. ------ *Note that some flatteners don't actually perform exactly to spec -- the label may say 55mm but your particular unit might be 56 or 54.5. If the stars at the corners are elongated while the center is round, you might have to tweak it. But start on-spec and work from there. Here's a diagram of what the errors look like:

Second the suggestion for APP's Remove Light Pollution tool. It's one of the suite's best features. My recent post shows what kind of nightmares that tool can solve. Have you played around with the different stretch settings in the right-hand panel? That's often a good start. I too was put off by the "data" jargon when I first started astro, but it actually serves as a good reminder of just how much work and intervention has to go between photons generating electrons in a sensor and a picture on the wall. Processing is at least half of the art.

There is actually a dark-sky park in Wisconsin, Bortle 1-2, up in Door County. I hauled my wife up there for a few days, figuring we could have fun during the days, I'd image and she'd play Horizon Zero Dawn at night, and I would sleep when we got home. If you look carefully you can see that the first image's field of view is almost contained in the second's; they were both shot with Pentax APS-C DSLRs, the Rho/Antares with a 50mm f/4 macro and the Milky Way with a 14mm Rokinon. The first one was mounted on my CEM70 with autoguiding and used a variety of exposures for about two hours of integration time, the second one was propped on a crate (I ran out of tripods) and was around a hundred 20" subs. The third and fourth images will be my "dirty laundry", the whackadoodle stuff I had to work with out of integration. I'll post those in a moment, just to show that you can actually extract a usable image out of data that seem impossible at first glance.

You need a Canon to M42 adapter -- I believe ZWO sell them on their site, not sure about the QHY folks. M42 (aka "T2") is one of the standard astronomy threads, with an 0.75mm pitch. You should be able to find an M42 filter drawer pretty easily. I don't know from Canon mounts, but this might be correct.

The gphoto driver used in INDI offers full support for the D3300, according to their web page. So KStars and Ekos should work for you. They run on Windows, Macs, and Linux, including Raspberry Pi's, which is what I use. It's an exceedingly full-featured suite so it definitely takes some hours to get your bearings, but it certainly works.

Concur. Just getting pointed at a target with that small field of view is no small challenge. There is all manner of tech to recommend but I think that would snow you pretty deeply at this point. My recommendation is to do exactly as alacant suggests, then once you've got focus nailed, at night you can figure out exactly what you're pointing at by uploading your frames to nova.astrometry.net. It's a slow process, but very easy. Eventually you'll likely end up with kit that lets you do it locally, in seconds. but just getting focused and on a target will be enough of a triumph. Heck, once you've got it focused, slew it over at the Milky Way and shoot a few! Plenty of tasty stuff in there. A possible deep-sky target with your rig, once you have focusing and pointing figured out, is M57, the Ring Nebula in Lyra. It's high in the sky, and it's pretty bright, so your tracking/autoguiding game needn't be Hubble-level to get enough photons for a recognizable image. It's tiny, so most deep-sky imagers don't get to it till much later, when they graduate to 2000mm focal lengths. 🙂 I am reluctant to tell someone "you're using the wrong gear, you MUST use what I use". That said, I did follow the "standard advice" of a short focal-length, fast refractor and a big sensor to start with and I'm very happy that I did. Deep sky is a tough game and no mistake, even when you go the easiest route you can find.

If £300 is way out, I would seriously consider the Pi/Astroberry route. Heck, it's almost as cheap as an intervalometer. If you want something cheap and turnkey, StellarMate OS: £46: Pi 4 4GB and power adapter £10: Case for Pi £35: StellarMate OS £10: MicroSD card That gives you a Pi 4B, like the ASIAir Pro, that you can control with a phone or tablet app to run an imaging sequence, perform polar alignment, do guiding, or indeed just about any observatory function. Though admittedly it lacks the the shiny red metal case of the ASI product. If you're looking at the old model of the ASIAir, you already know my opinion about plate solving on the 3; that's something you will want, at least someday.

astronomy.tools has a bunch of very useful calculators, including one for filter sizes for a given sensor size. The 294 looks like a fair bit more camera for a little more money, though you have to be persnickety about your calibration frames (e.g. don't scale darks, shoot to the exact exposure time of lights, likewise for dark flats if you use those). It has pretty serious amp glow. That's not a deal-killer -- my 183MM Pro does too -- but you do have to pay attention.

On my Pi 3, I could never get plate solving reliably working. On the 4, it's a few seconds. I never tried using binning with a DSLR, but it's not completely inconceivable that the driver will cause it to shoot a lower-res (read: faster-downloading) image for PA. Or you could just change the resolution on your camera yourself if it lets you do that while USB-ing. Maximum binning (minimum resolution) is absolutely fine for this purpose. If you have the 120 mounted to a guide scope, that will work perfectly well for PA, it doesn't have to be perfectly collimated with the mount axis or the imaging camera. I just tried out Ekos's PAA far, far away from Polaris last night -- I am talking pointing to a random sky patch at about 130°. Since I couldn't manually line up with Polaris to get the mount in the neighborhood to start with, it took several go-rounds, my initial error was over three degrees. But according to PHD, I nailed it within 2 arcminutes.

If you are just starting, I would heartily recommend that you accept the aberrations and start with the refractor. Or even pick up an old 200 f/4 Pentax telephoto and a Canon adapter. No, really! Learning astrophotography is different from doing productive astrophotography, and if you already have challenges from your mount, you'll learn faster and swear less at 500mm than at 1000, and 200mm would be better still. You will need to learn to polar align your mount to within arcminutes. You will need to learn how to focus more accurately than you ever have before, without autofocus. You will need to figure out how to get the danged target in your field of view (don't laugh, I have wasted significant fractions of a night struggling with merely that). You will need to learn how to run your acquisition program to guide and shoot. You will need to learn a processing workflow. Just about every one of these will introduce problems with your images till you get it right, and diagnosing where the problems are coming from is its own skill set. If you modify the Newt, you have introduced a whole new category of possible error sources. Are the stars bloated due to focus problems? Tracking problems? Improper processing? Introduced misalignment of the mirrors? Every added millimeter of focal length just exacerbates all those errors. Short refractors are recommended to beginners because they're the simplest things that can possibly work. If you want to cannonball into the deep end and enjoy yourself, please don't let me stop you. People do succeed with crazy-hard setups. But there are a lot of people who've said "Geez, I wish I'd started with something shorter". [Notices date on original post] Oh, dear. I guess my advice is either moot or they've learned the lessons anyway by now...

If your DLSR is connected to the Pi (and supported by INDI), you can run the Polar Alignment Assistant with it. It does require that plate solving be working, but that should go OK pretty much out of the box with Astroberry (I use StellarMate OS, so I'm hedging a little bit there). I remote into my Pi with a laptop for initial setup, just because it's convenient to have a keyboard. But I've done it plenty of times with just a tablet too. StellarMate OS (US$50) includes an app specifically optimized for running your Ekos system from a mobile device. I've had troubles getting it to connect but many swear by it. [Edited to add] The PAA now works on any part of the sky -- you can align using it even if Polaris and its environs are completely obscured. Haven't tried that yet personally but it's quite the feature. Of course it helps to have your mount pointing somewhere close to the Celestial Pole.

Yep. I would add that you should point at the meridian, right about at the celestial equator, to do the test. If the camera is horizontal WRT the horizon, RA will be side-to-side, DEC up and down. Or you can leave the tracking off for part of a long exposure to make a nice trail oriented right in the RA direction, then turn tracking on to hopefully make a dot. If it's not a dot, comparing the elongation to the initial trail will tell you whether it's PE or DEC drift from polar misalignment.

I am a big fan of Charlie Bracken's stuff generally, and the Astrophotography Sky Atlas is no exception. He has a list of 103 "best" AP targets sorted by culmination date, e.g. later in June the Lagoon Nebula will be as high in the sky as it ever gets. That gives a great first cull on great targets, and then you can use Stellarium or Whatsup to narrow it down to what you'll be able to see. I have an exceedingly limited sky at home, I had been thinking about a custom landscape for Stellarium but I'll have to try Whatsup. My other source, for narrowband, is over at Cloudy Nights. Our dear departed friend and master AP Goofi published a great list of emission nebulae, broken out by season and listed in RA order so they, too, are more or less in calendar order. You don't have to be a CN member to view the lists.

Tammie represent! I've used the Tamron 500 mirror for a fair old lot of stuff. Actually acceptably sharp -- IF you can get the ruddy thing focused. (Non-astro example; considerably less-compelling astro example) Topaz Sharpen AI does miracles with it, too. If you're going to use plate solving, eh, don't bother star-aligning your mount. Just get the polar alignment dialed in good and proper, Ekos will sync the mount to the plate-solved solution to higher accuracy than you can achieve anyway. If you do a Capture and solve / Slew to target, it syncs the mount along the way, no need to do a separate go with the "sync" radio button checked.

Bit of reprocessing -- calibrated first the background and then the star colors in APP, denoised and sharpened again, then pulled into Photoshop to yank like heck on the saturation sliders. Mostly for the stars, I dialed the galaxies back to that honey color although I think I overdid that -- could be whiter. Hit both the denoising and sharpening harder, so now there's more visible detail in the galaxies.

And it certainly produced a better image. Still lacking star color, but that's fixable with more integration time. About the only issue this time was when the Pi got so stuffed up that it wasn't responding to mouse clicks or keyboard events for 30-40 seconds at a time. Did not seem to be the connection, especially since I was out in the field and right next to the scope (WiFi and Mac Screen Sharing to VNC on the Pi). May have to look into booting and running off an SSD instead of the MicroSD card. At any rate, an hour of luminance and 30 minutes each of R, G, and B, 60" subs, 110 gain, ASI 183MM on a Stellarvue SV70t-IS riding a CEM70. Full tech at Astrobin, as always. What a beautiful night, out in the lonely farm country listening to the coyotes and barred owls.

You are absolutely right that a lot of things have to go right for an image to appear. The upside is that when you produce an image like this, you can brag about how many things you had to get right for this to work! I got a really cheap red/green dot rifle sight for my DSLR, with a simple little aluminum adapter to mount it on the hot shoe. Made a world of difference. I don't see that particular product on Amazon right now (Astromania). I use plate solving now but when that fails, I'm basically thrashing around just like when I started.