Color Imaging Train: October 21, 2018
Here's my working color imaging train with the William Optics GT81 APO. The leftmost component is the William Optics FLAT 6AII field flattener/reducer which brings the focal length of the GT81 to 382mm at f/4.7. Pretty fast. The problem, of course, with reducers and flatteners is nailing that 55mm T2 distance to the camera sensor. That means the off-axis guider has to be thin (Orion Thin OAG) and the inline filter drawer does as well. The last piece of the puzzle, or bit of trouble you have to deal with is focusing the off-axis guide camera, matching the guide camera sensor distance to the primary camera sensor distance. And I finally had a bit of clear sky at night--bright moon however--to dial this in.
I added the filter drawer to be able to support UHC and other filters with the ZWO ASI071MC color camera. I don't plan on running with a filter most of the time, but some targets call for a bit more contrast.
Posted October 21, 2018
Astro Gear: May 30, 2018
Narrowband imaging on the cheap?
It's tempting to say "here's what you can expect from a $129 Hydrogen-alpha filter", but it's never as simple as that, is it? Perspectives and opinions vary, but I consider this a pretty good H-alpha narrowband shot of the Crescent Nebula (NGC 6888), with some great contrast--the Crescent structure itself stands out, and I still managed to bring in a lot of the surrounding dust and clouds of ionized hydrogen. I used an Astronomik 1.25" 12nm Ha filter, an Atik 414EX mono CCD, iOptron CEM25P EQ mount, and I took 4 x 1200 second subs + 15 dark frames, all stacked in DSS. I shot these frames from my backyard, on a clear night with good seeing (Bortle 4, SQM: 20.62 mag/arc sec² according to https://www.lightpollutionmap.info). I've never shot deep space objects with 6, 5, or 3nm bandpass filters, but a 2" Baader 7nm used to be my primary Hydrogen-alpha filter--and I loved it. When I started out in astrophotography I was thinking long-term and went with 2" filters for everything--and it cost me a bunch. A couple years ago I switched to 1.25" filters, both for cost savings and pairing with the smaller Atik 414EX sensor--2" wasn't necessary. It also allowed me to get the Atik EFW2 with the 9-position filter wheel, so I can run with LRGB, Clear, Ha, OIII, SII, near-IR all in one neat motorized package. Because I was looking to save to money I went with a cheap Ha filter--the Astronomik 12nm H-alpha runs around $130 USD. Very inexpensive when compared to the $300 2" Baader I used to use regularly, and nowhere near the $900+ Astrodon 3nm 2" filter. I'm sure the Astrodon kicks ass--they're one of the premier filter manufacturers. But do you need a $900 filter to shoot narrowband? If you have fairly dark skies in your neighborhood (or within driving distance), I would say absolutely not. Will it make things easier when it comes to increasing SNR in light polluted skies? Absolutely. Will it make things easier when it comes to increasing contrast and pulling in those fainter wisps of dust and hydrogen? Probably. But I wouldn't hold off on narrowband imaging just because you can't afford the best. There are just too many cool targets in the night sky that you're not going to pick up with RGB. And that's one of the advantages of our hobby. You can shoot forty subs tonight, stack, process, and post them, and then come back tomorrow, next week, or next year and reshoot the same target with a different camera, faster scope, or better filters. Some targets never get old, and if they do, there are mysterious absorption nebulae and integrated flux nebulae--and even crazier things in the night sky to pursue. Beyond that, there are always interesting new wonders below the horizon--or above, depending on which hemisphere you spend most of your time.
Short thread on this topic at Cloudy Nights: https://www.cloudynights.com/topic/612314-7nm-vs-12nm-h-a-filter
The general conclusion is get the narrowest bandpass you can afford, which is the right answer, especially if you have any light pollution problems.
Posted May 30, 2018
Astro Gear - January 14, 2018
Astrophotography - Leveling Up
Something strange and wonderful happened over the summer, and at the time I was wondering if it was a unique couple days. Well, it has continued, and looks like it’s here to stay. I seem to have made it to the next level. How do I know? Not only am I taking 5, 10, 20-minute subs with narrowband filters, they look good. Really good. Okay, so I’m not in the same set with the astrophotographers posting some of the really impressive dark nebulae, integrated flux nebulae (Yes, the mysterious IFN), and other deep sky objects out there on Astrobin and elsewhere, but I’m very happy with the images I’m getting out of my equipment.
There’s a process we go through when we set out on this whole astronomy and astro imaging path--from beginner to wherever you are now. A process when we learn how to use new equipment, when we set up an equatorial mount, work through the intricacies of guiding, alignment, processing images, automating our gear with ASCOM or INDI—and whatever software you’re using on top of these protocols for observatory control.
We learn in different ways, but there’s one part of the process all of us have or will experience--I’ve experienced this four or five times over the last few years: one day you set up your EQ mount and OTA, you start everything up, your alignment process goes smoothly, you slew to your first target, focusing just works, plate solving and tracking have pinned your view down to the exact few arcseconds or degrees in the sky where you want to shoot, and suddenly you’re leaning back during 20-minute subs, thinking about things that—as someone who’s obsessed with astronomy—you should be thinking about on a night out under the stars, like: isn’t it amazing that the light allowed through the really narrow bandpass of the Ha filter to touch the CCD sensor on my camera has travelled 23 million lightyears through 2.176 x 10^20 kilometers of interstellar space, through the earth’s atmosphere to get here--to get to the telescope and camera I just set up in my backyard. Or maybe you’re thinking, hey, the neighborhood around Cassiopeia and Cepheus really is a kick-ass part of the sky when it comes to interesting nebulae. It’ll be something like that.
That’s the day things just work, and from that day forward (apparently) they continue to work--for the most part. Things click effortlessly together, and you’re not thinking about problems with focusing, or why the guide camera keeps losing the guide star, or any of the thousand other pieces of the astro-imaging process that can ruin that night out under the stars. It’s as if you’ve leveled up. All the accumulated knowledge, failures, weirdness in the system you’ve experienced--all the troubleshooting you’ve done over the last few years has seeped into your brain to become automatized behavior. And stuff that was difficult a month ago is now second nature. It’s like that happy moment in a good D&D game when you add up the points and you’re suddenly a level 8 Paladin Astrophotographer. It’s a damn good night.
And don’t worry if it this hasn’t happened yet--or recently. That only means if you stick with this astro stuff you’ll level up soon. Even if you’d like to, you won’t forget the frustrations of last night--as time-consuming and apparently wasteful they may have appeared. You’re learning from them. You’re picking up details you may not even be aware of, and you’re packing them away for the next clear night.
Here’s to clear skies. Go find them!
Posted January 14, 2018
Astro gear - December 25, 2017
My Winter Astro Setup, essentially the same William Optics GT-81 - iOptron CEM25 combo, with the addition of the iOptron Tri-Pier Adapter, some 6x8 aluminum plates off eBay, and one treated 4x4 post from Home Depot.
The good side of winter and astrophotography is it’s usually dry on clear nights--and “clear” really means clear in terms of astronomical seeing, atmospheric turbulence and all that. Downside is that it’s freakin’ cold. Tonight it’s supposed to get down to about -8°C (about 20°F), pretty cold to be out for a long time, but not painfully cold.
Here are a couple shots of my setup for tonight--and possibly the rest of the winter. (William Optics GT-81, CEM25P EQ mount, Atik414Ex mono CCD, WO 50mm guidescope with ZWO ASI120S-MM guide cam, INDI/KStars/Ekos observatory control). What’s cool is that I can unbolt the mount with the pier adapter and aluminum base plate (they’re all bolted together) from the 4x4 post and top plate, and carry in the entire setup--mount, scope, cameras, etc. What I especially like about this is the ease with which I can setup and tear down each night. The whole thing remains balanced and ready to go, with polar alignment reduced to very fine adjustment to zero in on the NCP.
Note on my other mount: I probably won’t use my Orion Atlas EQ-G mount until spring when things start to warm up, and that’s based on the weight of the Atlas and the low temperatures--with ice adding some difficulty to the setup process. (Yeah, I don’t want to lug around this monster with any probability of slipping, landing on my back, and having to catch fifty or sixty pounds of metal out of the air before it kills someone). The average winter low in New Hampshire is around -12°C, and the average winter high temp is still below 0°C (around 30°F). It’s not unusual for things to get down to -20 to -30°C (-10 to -20°F). We’re still in December, so early in the season, but we’re already getting repeated snow storms interspersed with temps above 0°C (32°F). We typically get a few days of warmer weather here and there, snow and ice melting weather, but there haven’t been enough of them to make a dent in the accumulating snow and ice we have in the yard, driveway, or back deck. We just ended yesterday (the 25th) with another 6 inches or so. When there’s ice, lighter is better.
Posted December 25, 2017
Astro Setup - September 23, 2017
What the backyard looked like last night. Sort of an astronomy campout under the stars. It was a pretty clear night. I hope you had clear skies wherever you were last night! (Nikon D3100, 18mm, 13 sec. exp. ISO 1600 - I used my son's camera for these shots because mine was hooked up with the AstroTech scope)
Here's one from last night's astro shoot: M42 - Orion Nebula (Yes, my favorite diffuse nebula). This time of year Orion doesn't start appearing over the horizon until the early morning hours. My Exposures started around 2am and ended around 5am. (Nikon D750, AstroTech AT6RC, William Optics field flattener/ 0.8x reducer; 162 light frames stacked in DSS, 140 dark frames).
And another shot from last Saturday night--of the Orion Nebula (M42) and De Mairan's Nebula (M43). This was the view from my other scope, William Optics GT-81 with the Atik 414EX monochrome CCD camera--which is just going to pick up a lot more of that good old ionized interstellar hydrogen.
