rickwayne

You might do well with it, but there are, as the Genie says in Aladdin, "a few exceptions, a few provisos, and a couple of quid pro quos". Hydrogen-alpha photography is mostly done of emission nebulae, where the gas is excited by starlight and glows with its characteristic deep-reddish hue. Other objects (reflection nebula, some galaxies) don't emit much and so aren't suitable. The 7nm filter lets through only a small slice of the photon flux (as I'm sure you know) so the sensor accumulates much more slowly. For my particular rig, for example, with an f/5.5 scope and a dedicated astro cam running at full-tilt gain, 10 minutes is a good sub-exposure time, and for a nice Ha picture I'll accumulate 2-4 hours of total integration. So depending on your optics and mount, you might not be able to run sub-exposures long enough to dig your signal out of the sensor's read noise. But heck, it's a hoot when it works!

APP should work your flats to completely defeat vignetting. If it isn't, something weird is going on. Have you tried comparing a sub in different modes in APP's viewer? Try looking at it calibrated and uncalibrated, with a good hard stretch set in the DDP panel on the right (more than you'd ever use to develop the image). Likewise, pull up one of your flats and stretch it till it screams, see if anything jumps out at you. Did you shoot flats for this session, or reuse a set? Are you sure the focus was in the same position?

Since hydrogen is so abundant, hydrogen emission is by far the brightest component in emission nebulae. It's a deep-red frequency that gets knocked down a lot by terrestrial cameras' IR-cut filters. However, if you image reflection nebulae, you'll get much less signal -- they tend to be blue (like scattering produces a blue sky). Really, these "light pollution" filters are a poor man's narrowband setup, so poorly adapted for broad-spectrum targets. For some kinds of lighting (e.g. sodium vapor) you can find filters that knock out just that particular line, but as LEDs proliferate, those become less useful. It's much more likely that you're losing Ha signal to the IR cut filter in your camera, rather than fighting light pollution per se. I mean, since the signal is dimmer the LP noise does drown it out more. But a better solution IMO would be to either get a modded DSLR, get a dedicated astro cam, or simply swamp your IR cut filter by shooting a crap-ton of integration time. I prefer to gather all the photons and fight LP gradients in software. Concur that a filter wheel is going to work much better if you wind up with a mono camera. Unless you have some whopping-huge sensor, you won't need a 2" filter (my IMX183 sensor does fine with 1.25" filters). And for that kind of camera, a luminance filter is best for the luminance layer. I know I sound like a smart-ass there, but it's one of the great advantages of a mono setup that you can use a luminance filter to rapidly gather all the photons onto all the photosites to gain maximum SNR where it counts most, since detail inheres in the luminance data due to the way our vision works.

Yeah, the trouble is that just about every expensive piece of kit is "Wow, it's so much better now I could never go back". You might wish, after the fact, that you had the money available again to do something else, but your astro-self will never regret acquiring a dedicated camera. Makes so many things easier, and if you go mono, you have a world of new possibilities too. RGB, LRGB, narrowband...I am really glad I dropped nine bills on my 183, tell you that for free. I think I will be glad I blew twenty-five of them on the CEM70, if we ever see stars again.

I was gonna say: Narrowband, homies. Chuck on that hydrogen-alpha filter and you're laughing.

Oh yeah, you're DEFINITELY the first. As we say of retractable-gear pilots, there are two kinds: Those who've made a gear-up landing, and those who will. (When I first checked out in such a bird, the fanged instructor so rewired my brain that whenever I flew fixed-gear a/c thenceforth, I still ran the gear checklist, except that the response, instead of "down and locked", was a look out the window and "down and welded".)

Yep. You've essentially turned your DSLR into a mono camera with 3/4 of its photosites inactive (most Bayer filters have double G sites, e.g. my Pentax is BGGR). So you'll need a lot of integration time to pull up the Ha signal, and only the red channel will contribute anything.

Concur. The number of photons hitting the sensor is the same except for noise effects whether you do a few long exposures or lots of short ones. But longer exposures will help dig signal out of the noise. I run 10 minutes at gain 178 on my IMX183 sensor for narrowband, at least when my guiding is behaving. Five works pretty well. Is there a reason that you're not running at the highest gain (i.e., lowest read noise) available? You're not going get good star color with narrowband so there's little reason to avoid blowing out the stars, and you've got oodles of well depth and ADC resolution anyway. Nice thing about your one-shot camera is that you can take a series of high-gain, narrowband images for nebulosity, remove the filter, and shoot much shorter exposures for stars.

Lucky you. I cross-connected the DEC drive cable on my CEM25P to the ST-4 port one night shortly after I got the mount...what's all that red smoke? (I had a red LED headlamp.) I pleaded in a letter to iOptron to make the labels readable. I mean, dark grey on black, for a bit of gear used IN THE DARK? Somebody's nephew got hired fresh out of graphic design school for that one. Failing that, at least ship the mount with empty RJ-11 plugs in all the ports, as markese68 suggests. Nada.

When the connections all work, an integrated suite like NINA, APT, or Ekos is a joy to operate. Of course then you can't image without a computer or tablet.

I was going to suggest the same -- unless it's a deep-cycle battery, best not to whang on it too hard or you'll shorten its life. I have one of these little meters wired into the harness for my battery (which is a deep-cycle). Takes next to no current, and it will not only give you the voltage going out, but also how many amp-hours you've consumed since the last reset. Very nice feature is that you can set a voltage-level alarm, which blinks the blue backlight. So you can safeguard your battery from too deep a discharge, when the voltage starts to drop, it will get your attention. Super-duper easy to wire up, no soldering required. I just stripped the wire ends and applied copious amounts of tape. https://www.droking.com/panel-meter/dc-ammeter/4in1-Voltmeter-Ammeter-Power-Meter-Energy-Meter-DC-6.5-100V-20A-2000W-0-9999kWh-LCD-Display-Blue-backlight-Digital-Meter I started with a 14 Ah battery which ran my CEM25P, Raspberry Pi, and cameras quite nicely for a few hours. A friend loaned me her 26 Ah monster, which in warm weather will go all night.

Yep! I bet it feels good to make this much progress. The GIMP is a terrific pixel-level editing program but astro has some special challenges that respond to purpose-built software. I've actually done some deep-sky images start-to-finish in Photoshop, stacking and all. It's possible, but it's like using a hammer to smooth wood before painting it -- just not intended for the task. In addition to calibration and integration, astro software like Siril (or Astro Pixel Processor, PixInsight, ASTAP...) offers functions such as gradient reduction and background correction (to get rid of light pollution effects), and can do an automatic stretch with a single button press that gets you almost there. One note about sub-exposures and integration time: longer integration time reduces noise (not just the "grainy" appearance, but lots of other problems with the image) in a square-root curve. So to halve the noise, you need four times the total exposure time. To cut it to 1/4, sixteen times. You can see that for short exposures, you get a lot of bang out of adding your first few sub-exposure bucks, but after that it's a game of diminishing returns. Basically this means you should go crazy on the number of subs you take, especially if they're short. M42 is a wonderful target, in that a beginner can get a really beautiful, satisfying result like yours, but there are just endless challenges to master for this one object. It has a very high dynamic range, so that you need to do something about not blowing out the central Trapezium if you want to capture the delicate, dim nebulosity out at the edges. It has both emission and reflection components. It has an incredible range of color. And, as you note, it's bright and big enough to find!

Perfect technique for reflection nebulae :-).

Flaming Star is my next target, assuming I can get my new mount to behave.

Field rotation is what happens without an equatorial mount. If you visualize, say, Orion on the eastern horizon, then track it overhead to the western horizon, you'll see that unless you rotate the camera, it will have flipped 180 degrees. Or, for a simpler example, if you visualize the Little Dipper going around the pole, keeping your camera pointed perfectly at its center doesn't mean that the constellation won't rotate in the FOV. Equatorial mounts do more than track a target, they also compensate for this effect. Field rotation is most notable at the edges of the field, which is why it shows up nicely with an ultrawide lens. The only way around it is (a) to rotate the camera in the same direction, which is the approach taken by some really big telescopes that physically can't be equatorially mounted, (b) use an EQ mount, or (c) use exposures short enough that the trailing isn't noticeable. There's an online calculator if you're interested. For focusing, try searching online for "Bahtinov mask". That's the best technique I know of for razor-sharp focusing without computer assistance. It is difficult, and no mistake.

Nice! There's always Bracken's The Astrophotography Sky Atlas if you want to hunt for good targets. Telescopius.com will put suggestions up for a given set of search parameters. I find that Stellarium (e.g.) is great when I know what I'm looking for, but having a premade seasonal list to work from means a lot less thrashing about. My other tactic is to subscribe to notifications from Astrobin on photographers whose work I particularly prize (e.g. Kathy Walker, pete_xl) and just shamelessly follow what they're targeting.

You've already done many of the tests and steps but in case you didn't have this one to hand (and for others reading this thread): https://openphdguiding.org/man-dev/Trouble_shooting.htm 1 second is not necessarily that short an exposure these days. Notice that the GA is recommending 1.8s as a drift-limiting exposure. I've found that 1s works pretty well with multistar guiding in PHD2, but of course that's with my rig and YMMV.

I guess my first question would be "why do you want an OAG"? In other words, what are you trying to accomplish? My second question would be "what limitations might your system have that would drive the choice?" For example, I have a field flattener/reducer with a 55mm backfocus. I can just get an OAG to reach focus with my filterwheel and ASI183MM behind it at the correct distance. If it's well-designed, of course, an OAG's optical path from the front of the unit to the guide camera mounting will be the same length as the one straight through. As you may know, one of the tricky bits in setting one up is getting the guide camera focused. Using my ZWO as an example, there is a setscrew to fix how far the stalk with the pickoff prism dives into the light cone, and another one that locks the camera as it slides up and down on the cone. It's a bit of a pain to focus by sliding a camera and then tightening the setscrew; one feature to look for is a helical focuser. In my case, there's no room in the optical path for such a thing. Another issue is how the thing assembles. I wanted all threaded connections for my rig, but there is one fitting in the ZWO OAG that slides in and is locked by setscrews. Sort of like an eyepiece, except there are three screws and the wings of the fitting are angled a little bit so that the force of the setscrew tends to pull it forward (i.e., tighter). It's the "M48 adapter" in this image (the assembled OAG has the M42 adapter installed).

WRT the Great Mono vs. OSC Debate, meh. You will be able to do great images either way. At the current state of the art, what really matters is setpoint cooling for noise reduction and consistency. Unless you're pretty far out under one leg or the other of the bell curve, you really won't miss whichever one you decide to eschew. I will say that personally I'm kind of perversely drawn to mono's greater amount of fiddle-faddle, just as I enjoy shooting old manual-everything lenses for terrestrial work. I had never even considered not bothering to refocus for the RGB filters. But...of course that make eminent sense! Given my Beverly Hillbillies focusing rig, that would probably add a nontrivial number of RGB light frames to a given imaging session. And if you're not refocusing between the filters, there's no reason not to interleave them, meaning that you don't have to get stuck with just e.g. LRG and have to wait for a year.

SMILE when you say that, son! Anyway, that's not true. We have cows.

One word for all of you mamby-pamby types who think you know what winter is: Wisconsin.

Your wife doesn't "borrow" your gear for her own astroimaging? Lucky!

Welcome! Maybe I'm just masochistic, but I figure if a ten-thumbed goof like me can manage something, it can't be THAT hard. I am, in fact, running an OAG on a short refractor, and while it did take a bit of sorting out, it's lighter, simpler to balance, and less bother overall than when I used a guidescope. Once I figured out where to put the pickoff stalk (hint: on the long side of the sensor) and how deep I could push it without vignetting, I have had pretty much zero issues. Focusing is one issue people struggle with, unless your setup allows a helical focuser you have to slide the camera up and down on its stalk and then pin it with its fixing bolt. But once it's set, you don't have to touch it again. What you're doing is adjusting the light-path length to the guide camera so it's the same as that to the imaging camera, so that when you focus the latter, the former is sharp too. The field of view and f-ratio are usually smaller and slower, respectively, so some folk have trouble finding guide stars. Never really been a problem for my 386mm f/5.5 refractor. Likewise mono and filters. The luminance filter is a royal road to good detail with overall shorter integration time, and the option of doing full-performance narrowband is HUGE for me. You can do narrowband with a tri-pass filter on a one-shot color camera, but it's much less efficient. Processing is also pretty easy. Admittedly I cheat and use Astro Pixel Processor.

Welcome! The classic advice is to minimize your challenges when first starting astrophotography, since there is an irreducible minimum challenge level that's fairly daunting to most folks. A small fast widefield refractor (e.g. 80mm, f/6 or better) is the easiest to mount and most trouble-free optical tube available. You want light weight and physically not too long to reduce the moment arm in order to reduce tracking challenges. Fast means that you can go with shorter exposures without running into trailing. Plenty of people succeed with longer, slower scopes, but quite a few of them express the wish that they'd started with something easier. The rule of thumb for astrophotography is to run a mount at about 50% of its rated capacity. You're treading on that for an HEQ5 even without including a camera, or anything to guide with. All that said, the other big rule is to spend till it hurts on mount, and accept whatever you can afford to put on it. If switching to an easier-to-learn scope would mean you dial back on the mount, you're better off either going with the optical tube assembly you already have, or mounting a camera and lens on it first and leaving the telescope for later.

Well, you don't have to bin with a 183. But they are pretty small pixels. The "sweet spot" for that sensor is a fairly fast, fairly wide-field scope like my SV-70. It's certainly a worthwhile camera. The price was one reason I went with it over the 1600. I have a Stellarvue flattener/reducer with a 55mm back focus, and am using it with an OAG and filter wheel. It just barely works, but it works. I have to get the pickoff stalk in just the right position and there's no room for a helical focuser for the OAG, so I have to focus the guide cam like porcupines make love: very, very carefully. But once it's set up, it works great. The 183 sensors have crazy amp glow. Absurdly so. Scaling darks is not an option, I absolutely have to have a set for each exact combination of temperature, exposure time, and gain. (That's a big reason I only use two combinations!) With that caveat, the glow calibrates out and great images can be obtained. Even I can do some acceptable ones (check my astrobin for examples).