I moved the Moonlite focuser from the William Optics GT81 to the AT6RC scope and spent half an hour getting the focus distance more-or-less dialed in. I'm focusing on a tree line about 1600 feet / .5km away. That transmission pole is almost 500 feet closer to me. I'm using the color imaging train with the ZWO ASI071C and a longpass hydrogen-alpha filter, which is why the test frame has that white-tree IR look. In the images with the setup you can see the color in the trees. It's a beautiful fall day out there, although I don't think it's supposed to be that clear tonight. Just have to wait and see!
According to the William Optics SpaceCat 51 backfocus specs, I have a 59.7 mm backfocus from the flange face of M54->M48 adapter. The SpaceCat has a different configuration from the first generation RedCat. It includes a tilt adjust ring with a 54mm threaded facing (Takahashi wide mount 54 mm, 0.75 pitch thread) plus an M54 to M48 (T2) adapter. I think William Optics designed the thickness of the last adapter to avoid changing backfocus specifications across the various cats. And so any configuration I have will work with the original RedCat 51s as well as other breeds--WhiteCat, BlackCat, and K-Astec Limited Edition.
I have two main astro imaging trains, and both come in under 57mm. The color train is a ZWO ASI071MC, 2" filter drawer, Orion Thin Off-axis Guider with QHY5iii178 guide camera. For daytime testing I threw in a 2" hydrogen-alpha longpass filter. My narrowband imaging train consists of a ZWO ASI1600MM-Pro, ZWO EFW (Clear, 6nm Ha, 6nm OIII, 6nm SII, 685nm Near-IR), Orion Thin Off-axis Guider with ZWO ASI120M-mini guide camera.
I set up the iOptron CEM25P this morning, and used SharCap Pro to test the focus for both trains. I'm happy with the results. The color train is a bit worrying because the ZWO ASI071MC has a crazy 17.5mm depth to sensor. I was able to focus on some distant trees, but the SpaceCat's focus ring was only slightly out from infinity. We'll see what my results are with the stars!
The ZWO ASI1600MM-Pro on the narrowband train only has a 6.5mm depth to sensor with the ZWO filterwheel, and I had the focus ring on the cat further out. Should be no problem with DSOs in this case. I may miss having autofocus though.
Some shots from my morning focus testing with the beautifully machined William Optics SpaceCat 51 apochromatic refractor.
I'm pretty sure I got the last one at Highpoint Scientific. I also bought the Cat Saddle/Handle-bar.
Let's take a look at the Space Gray version of the William Optics Cat Saddle/Handle-bar. That is a beautiful piece of hardware.
I didn't have much time last night, so I just went with the Nikon D750 + 70-300mm lens on the iOptron SkyGuider Pro. And shot 20 exposures of M31. I was actually just wheeling the camera around the sky, adjusting focus at 70mm when I saw Andromeda Galaxy in the upper left, and there was M33 Triangulum in the lower corner. This is cropped from the full image, and I probably could have framed these better, but I didn't feel like pushing my luck. M33 was down by the bottom edge. So I went with this, 20 stacked frames in DSS:
And then a little later I shot 51 25 second shots of M45, the Pleiades--this time at 300mm:
The Andromeda Galaxy (M31) is our largest and most magnificent galactic neighbor, about 2.5 million light-years away from earth (or 780 kiloparsecs if you're of a more serious demeanor). Here's my bi-color version in near-IR and hydrogen-alpha. With a 685nm IR longpass filter I have managed to get a ring in M110 (NGC 205) the dwarf elliptical galaxy and satellite of Andromeda (center bottom). Wasn't expecting that. I am assuming the rings are an artifact of processing or cut-out gaps between bandpasses in the filtering because M110 is an elliptical galaxy, which are evenly distributed bundles of stars without arms or distinguishable belts like a spiral galaxy, e.g., M31, Milky Way.
Anyway, I'm enjoying the variation I'm getting with infrared imaging. More on the way! I may upgrade to the Astrodon Sloan Gen2 i’ (695 - 844nm) near IR filter at some point, but I'm happy so far with the results of the less expensive Optolong 685nm.
M31 in color, one my images from early this year:
This is my second attempt with Sh2-132, sometimes called the "Lion Nebula" or "Lion's Mane", a roughly square-shaped emission nebula--or diamond in this rotation. Sharpless 2-132 is very faint and tough to capture without resorting to 10 or 20-minute exposures, which in turn requires outstanding alignment and guiding, not to mention a cooled camera and a good stretch of clear night sky. I ran at a steady -20C for 31 exposures. Sh2-132 is also in the middle (or behind) a dense field of stars, and that makes processing difficult when you're trying to bring out those faint cloudy structures. It's just too easy to bloat and overexpose the stars at the same time. All about balance with stretching and keeping an eye on your stars!
So far I have only captured hydrogen-alpha frames. Sh2-132 also has a strong band of oxygen, stretching from the bright lower corner to the top. Find Sharpless 2-132 in the Perseus arm of our galaxy, on the border between the constellations Cepheus and Lacerta.
Imaging notes: William Optics GT81 at f/4.7 with WO 0.8x Flat6A II, Astronomik Ha 6nm filter, Moonlite focuser, ZWO ASI120MM OAG, Imaging camera: ZWO ASI1600MM Pro cooled mono on an Orion Atlas EQ-G mount. Stacked in DSS, processed in PS CC 2019. 31 x 600 second exposures.
I have been thinking about how to represent false-color imaging for deep sky objects, and I've been keeping more of that abundant hydrogen green in the mix when doing SHO Hubble Palette images, where we map Sulfur, Hydrogen, and Oxygen bandpasses to Red Green Blue (RGB). Because hydrogen is--by a wide margin--the most abundant element in the universe, and many of these nebulae are HII Regions (vast expanses of interstellar ionized hydrogen), there ought to be more green in SHO images than we normally see. It's become standard to go heavy on a rust red and deep blue, with most of the green removed. All of these color choices are esthetic choices. The images I'm posting come from the data from three separate filters, Ha, OIII, and SII, so in a sense there are no incorrect color levels--within reason.
You do see a lot of color (LRGB) imaging with a target like M42, and with corresponding heavy reds and browns of bandpasses on the red end of the spectrum--and heading off into infrared. Most of my shots of Orion Nebula from past years has been in RGB with a luminance layer.
In the first set I toned the hydrogen green way down--actually all the colors are lower--until I'm just getting a nice green cast over everything.
I expanded on this in an Astrobin comment, dropping it here:
I'm going to reprocess data for some recent targets, see how they turn out. I think the reasoning is sound--that we should see more green with SHO, but we'll have to see how the images look. I know many handle this already by going with HSO to map Ha to Red, which makes a lot of sense, closer to where Ha is on the EM spectrum, even if we put sulfur in Green with this pattern. At the end of the day, though, it's still about how beautiful these images of nebulae look, and how each of us measures that beauty. It could also be that dozens of others have gone through this exact cycle with color levels and patterns and ended up back where we are today, simply because the stronger blues and reds are more appealing! I think one of the best things about this hobby/obsession is that it's data driven, and when I get new data and I try new techniques--and I like what I see, I can go back and reprocess data and try these techniques on other targets. There's something very powerful about this.
M42 Orion Nebula with the stars removed. I used the star removal in Annie's Astro Actions in Photoshop, which gets you 90% there, with some cleanup around the remnants of larger stars. Okay, this looks like H.R. Giger's version of the Orion Nebula.
To show you what I mean by "no incorrect color levels", this is the same imaging data, from the same stacked Ha, OIII, and SII frames. I just went in a different direction with which bandpass to stress--oxygen in this case, with stronger blues. It's strange how the "running man" shape in Sh2-279 Running Man Nebula, the brightish cloud above Orion, only appears faintly in narrowband. And in Orion, on the bottom right side, there's the weird chicken leg of hydrogen that now stands out behind the wispy pale clouds that ring the nebula.
And here's the same data set in HSO, with hydrogen-alpha mapped to red in RGB, sulfur green, and oxygen blue. You could argue that this is slightly more natural, as the hydrogen-alpha line is off the red end of the visible spectrum at 656nm, just this side of infrared. Mapping Ha to red makes sense, but mapping sulfur to green doesn't. The sulfur line is also on the red end of the spectrum, which is why normal RGB images of most deep sky objects taken with a DSLR or OSC camera are usually very red.
Imaging notes: William Optics GT81 at f/4.7 with WO 0.8x Flat6A II, Astronomik Ha, OIII, SII 6nm filters, Moonlite focuser, ZWO ASI120MM OAG, Imaging camera: ZWO ASI1600MM Pro cooled mono on an Orion Atlas EQ-G mount. Stacked in DSS, processed in PS CC 2019. 40 x 120 second exposures for each filter.
NGC 7822, Sharpless 171, Ced 214 region, along with the star cluster, Berkeley 59 at the top left. The bright core on the right is a massive star-forming complex that lights up most of the surrounding clouds of interstellar hydrogen and oxygen between Cepheus and Cassiopeia.
Imaging notes: William Optics GT81 at f/4.7 with WO 0.8x Flat6A II, Astronomik Ha, OIII filters, Moonlite focuser, ZWO ASI120MM OAG, Imaging camera: ZWO ASI1600MM Pro cooled mono on an Orion Atlas EQ-G mount. Stacked in DSS, processed in PS CC 2019. Bi-color Ha and OIII, 13 x 300 second exposures for each filter.