Here's my first night out with the Irix 15mm f/2.4 Blackstone (the heavier, more durable, aluminum and magnesium alloy housing version of this lens). And I'm impressed with just a few shots, wide-open aperture, and single 15 - 20 second exposures--no tripod, although I rested the Nikon on the deck railing.
I've had the Orion Atlas EQ-G, William Optics GT81, and ZWO ASI071MC camera set up for the last three days. It's been cold--down around -10C in the early morning hours. With a new moon that's slowly waxing, but still mostly absent from the night sky, I've been using the color camera to capture some amazing targets, including this three panel mosaic of the Orion Nebula (M42), Running Man Nebula, Horsehead Nebula (Barnard 33), Flame Nebula (NGC 2024), and the three giant stars in Orion's Belt, Alnitak, Alnilam, and Mintaka. This is why the Orion Constellation is arguably the sky's most impressive constellation. NOTES: 31 x 300 second exposures for each, with an additional set of 10 and 30 second exposures for the Trapezium in M42--that really bright triangular region. There's just so much fiery star forming action at the heart of the Orion Nebula that any exposure over a dozen seconds is going to blow out the whole area.
Here's my setup for the last few nights:
Orion at the southern Meridian:
First shot of the season in the constellation Orion! I set up the AstroTech RC scope (6"/152mm aperture f/9) with my narrowband imaging train, Atik 414EX, ZWO filter wheel with Clear, Ha, OIII, SII & IR685, William Optics 0.8x field flattener/reducer that brings the AT6RC to f/7.2 at 1080mm focal length. With the Atik's 6.45μ pixels this has my resolution at 1.23 arcseconds per pixel, and a field of view of 0.48° x 0.36°.
Here are some shots of my set up last night, before nightfall, and in the middle of the narrowband run with 600-second exposures.
The 1000mm+ focal length did get me wonderfully close to the Horsehead Nebula (B33) and the reflection nebula NGC 2023 (bottom left) in the constellation Orion. This is what 46 stacked 600 second hydrogen-alpha frames will get you if you stretch things a bit too much and don't use any calibration frames. That would reduce the noise/graininess somewhat. Anyway, pretty happy with this. (46 x 600 second exposures in Ha, Atik 414EX mono CCD at -10C, Astronomik 12nm Ha filter, AstroTech AT6RC f/9 Ritchey-Chrétien + WO Flat6A f/7.2, iOptron CEM25P EQ mount, Orion OAG + ZWO ASI120MM-Mini guide cam, Stellarmate OS (INDI/KStars/Ekos) running on Raspberry Pi 3b+. Stacked in DSS, processed in Photoshop CC 2019).
I stretched the hell out of this stack of 46 x 600 second subs, mainly to see what the data would show if I went out of my way to bring out the details. I also didn't use dark frames with this--so that's worth a try. The Atik 414EX at -10C or cooler is very clean, though. I usually don't gain a lot with calibration frames, but in this case even a little will improve the noisiness.
I don't use the AT6RC scope that much, mostly because when paired with the cameras I have the resolution is oversampled crap. The Atik is the only one that's right in there at 1.23 arcseconds/pixel, and that's with the 0.8x field flattener/reducer.
Another point (or set of points) I would like to make is the Astro-Tech 6" f/9 Ritchey-Chrétien is a $400 scope, and I'm pretty impressed with the light and contrast it managed to pull out of the night sky. Some of the credit certainly goes to the Atik CCD, which really is an amazing little camera. The sub-$1000 iOptron CEM25P has no problem with long exposure times. Along with the $129 12nm Astronomik Ha filter, this is a very inexpensive narrowband setup. The point being you don't need to spend a raft-load of cash to start capturing those beautiful HII regions, supernova remnants, and other wonders in the night sky.
My tips for the iOptron CEM25P--or what I've learned over the last two years: For narrowband, I normally shoot 5, 10 or 20 minute subs depending on the brightness of the target, and the iOptron has no problem. However, there are a few steps I go through in order to get very long exposures from this mount. 1) a solid foundation--solid tripod or better. I don't have a concrete or steel pier, but I do have a treated 4x4 solidly in the ground, and it doesn't move. 2) More counterweights, closer to the center of balance. I try to use more weight, and keep them as close to the top of the counterweight shaft as possible. I know it's tempting to use fewer weights farther out, but trust me on this--and don't worry about the bushings that carry all the weight. They can handle far more than you'll ever bolt on. It's minor, but it does smooth out tiny movements the scope has to make--so improved guiding. 3) Balance, balance, balance. You want a perfectly balanced scope and equipment. Don't bias weight to one side; don't get your gear "close enough". If you'll permit me to anthropomorphize the CEM25P for a moment, you want the mount and motors to think they're moving nothing at all, and for that you'll need to balance the shit out of your payload. I use small 100g camera gimbal weights to even the load--balance is that important. (https://www.amazon.com/gp/product/B0797S81HR)
Okay, I also took some subs of the Triangulum Galaxy core (M33) while setting up and getting into focus--testing out shooting in 2x2 binning, which reduces the resolution by half.
I took the Nikon D750 out tonight and got a nice 30 second exposure of the constellation Orion (upper right of the first image), with some of the PSNH transmission lines in the foreground. That's Sirius almost center in the shot, with Procyon on the upper left. Centered in the image about a quarter of the way from the top, there's a reddish blur between the star Procyon and the star Betelgeuse in Orion--that's the Rosette Nebula--see my December 26 post. (Nikon D750, 24mm, Hoya LiPo filter, f/4.5, 30 sec. exp. ISO 800). The second shot is M44, the Beehive Cluster in the constellation Cancer--plus a few more stars. (Nikon D750, 24mm, Hoya LiPo filter, f/4.5, 1 x 300 second exposure, ISO 800). These are both single exposures, and I shot both on the iOptron CEM25P mount, and what amazed me was that, with pretty good polar alignment, just using the polar scope (no drift or polemaster), I was able to get 3 and 4 minute exposures unguided. The M44 shot is 300 seconds (5 minutes) with some slight star elongation, but still not a bad shot.
The color of stars is interesting to look for--take a closer look at the Beehive Cluster (M44) image and it's easy to see that the star-field is full of color. I think there's this notion that stars are white pin-points of light in the night sky, but every star has a color, most of them ranging from red to deep blue, depending on many factors including where in its life-cycle it is, the materials it's made from, size, and more. See the Hertzsprung-Russell diagram, listing some of the more familiar stars in our galaxy by surface temperature and luminosity. Our star, the Sun, is pretty close to the middle of the Main Sequence line, between cooler, redder stars and the hotter blue stars. What's interesting is that the shot of the constellation Orion I took the other night--included here--contains several of these stars from the diagram. If you start at the Sun and follow the Main Sequence line up toward the blue end, you will quickly find Procyon, which is the bright star in the top left corner of my image. Sirius--in the diagram--is a couple up from there, but it's almost in the center of my shot. Keep going into the blue, and there's Bellatrix, the blue star which makes up Orion's right shoulder. Now head right from there, out of the Main Sequence line and into the Supergiants, and find the blue supergiant Rigel, which makes up Orion's right foot. And finally, keep going right to the massive red supergiant, Betelgeuse ("Beetle-juice"), which is the left shoulder of Orion. (Hertzsprung-Russell diagram source: ESO - European Southern Observatory, ). How's that for taking one picture of the night sky with some nice examples of stars of varying size, color, and lifespan?
A couple test Ha frames of Lower's Nebula (SH 2-261) in the constellation Orion. I only took two exposures of Lower's Nebula while waiting for the Rosette Nebula to rise, and it reminded me of a scene in the movie Roxanne with Steve Martin (CD Bales) and Daryl Hannah (Roxanne):
C.D. Bales: You must know about M31.
C.D. Bales: Now, see, I like it when they give astronomical objects names, you know, like "Andromeda" and "Saturn" and "Sea of Tranquility." This whole numbering thing is just too boring for us civilians.
Roxanne: Do you know how many objects are up there?
C.D. Bales: Well, I know it's over fifty.
That's the problem when you're a constellation like Orion, with a nebula so massive and bright you can see it clearly without a telescope (M42), or you possess dark nebular structures famously shaped like animals (Horsehead nebula, Barnard 33). You get overlooked if you're not a superstar or supernova remnant or "The Great" Orion Nebula. Yeah, that's Lower's Nebula (SH 2-261), which I'm sorry to say, I had never heard of before last night. Unfortunately that's probably because Lower's Nebula isn't the buckle on Orion's Belt. It isn't even hanging off of Orion's famous belt. It is literally out on a distant arm of the constellation--yes, Orion has one arm raised, far away from the Belt, and the famous stars like Betelgeuse, Bellatrix, and Rigel, and that's where you'll find this obscure cloud of hydrogen that doesn't even have a wikipedia page (In English. I found an Italian page for SH2-261. Nicely done, Italy.)
(Subframe info: one 600-second exposure and one 1200-second exposure stacked in DSS, no calibration frames, Atik414Ex mono CCD running at -10C, Astronomik 12nm Ha filter, William Optics GT-81, CEM25P EQ mount, WO 50mm guidescope with ZWO ASI120S-MM guide cam, INDI/KStars/Ekos observatory control)
Constellation Orion (and that's Sirius in the lower left). I was out in the cold last night, with the Nikon D750 (24mm, 30 sec. exposure, ISO 800). Love that Hampton sky glow.
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.