Configuring an Off-axis Guider with the SpaceCat

Just wanted to document the spacing and backfocus distance for the ZWO ASI1600MM-Pro with the electronic filter wheel and OAG. The William Optics SpaceCat 51 allows a maximum distance of 57.9mm to achieve minimum focus, so I like to be somewhere close to 50mm when everything is totaled up--and looking good:

  • ASI1600MM 6.5mm
  • ZWO EFW 20mm
  • M42-M48 ~5mm
  • M48 spacer 5mm
  • OAG 10.5mm
  • 42-M48 ~3mm

Total: ~50mm

Posted September 7, 2022

NGC 1499 in Ha

The California Nebula (NGC 1499) in the constellation Perseus. Imaging notes: 3nm Antlia Pro hydrogen-alpha filter, William Optics SpaceCat 51 Apochromatic refractor, ZWO ASI1600MM-Pro monochrome camera. 

Posted September 5, 2022

Dual Imaging Rigs

A shot of my backyard last Friday. It was nice and clear, and I ran both imaging systems, the 250mm monochrome camera and narrowband (NGC 281, Pacman Nebula in Cassiopeia), and the 800mm with filtered RGB color (M33, Triangulum Galaxy).

Posted September 5, 2022

M31 and M33

I used the Optolong L-eXtreme for half of the exposures, filtering out everything except 7nm lines along hydrogen-alpha and oxygen 3, and then switched to full broadband, just the UV/IR Cut Filter. Notes: 8" 800mm f/4 Newtonian and the ZWO ASI071MC cooled color camera.

I'm not really a galaxy guy, more of a nebula guy, mainly because I don't have a scope over 1350mm, which is just long enough to get a handful of nearby galaxies. So, for now, I usually capture a couple of our galactic neighbors when they swing around this time of year--and if the moon and clear night skies line up for broadband color imaging! 

The central region of M31, Andromeda Galaxy:

The Triangulum Galaxy from my backyard--it's only 2.73 million light-years from Earth! I've said it before. Once we develop MFTL technology (Much Faster Than Light) and we have the ability to hop to nearby galaxies, count me in on a trip to M33, the Triangulum Galaxy. The chunky pinkish masses are vast regions of interstellar ionized hydrogen that make up the nebulae in M33, perfect for an astrophotography outing. Until then, maybe we can take a trip to the southern hemisphere? Notes: Apertura 8" Newtonian OTA--800mm at f/4, ZWO ASI071MC cooled color camera. Optolong L-eXtreme dual narrowband filter. 48 x 240-second exposures stacked in DSS. 

Posted September 4, 2022


A wide-field view of the Pacman Nebula (NGC 281, IC11, Sh20184) in Cassiopeia (Ha + OIII), about 9500 lightyears away. The massive star on the right is α Cassiopeiae (or "alpha Cass" if you're on friendly terms) which makes up the right lower point of the W asterism of the constellation Cassiopeia. The bright star at the top is eta Cass, a binary star system that's only about 20 lightyears away from us, downright neighborly, and is not part of the W asterism. 

Posted September 4, 2022

Cave Nebula, part one

The Cave Nebula (Caldwell 9) in Cepheus. I started the Ha run last night but Earth's atmosphere wasn't having any of it. Seeing was poor at best, and the random wisps of cloud passing through just made it worse. I stacked the first 30 subs just to see where it was going, and even with the excessive noise, I think this is headed in the right direction.

Posted September 1, 2022

NINA/ASCOM: Connect your ZWO AM5 Wirelessly

Tonight's test with the ZWO AM5 mount: run a virtual USB server from a Raspberry Pi and connect wirelessly to the AM5 from my Windows machine running NINA/ASCOM. The VirtualHere server is running on the Raspberry Pi, with the ZWO AM5 mount connected via USB The VirtualHere Client, running on my Windows astro controller, creates a standard COM port for the connected device (AM5). The ZWO AM5 ASCOM driver connects normally, and everything functions as if the AM5 is plugged directly into the Windows computer.

See my older post on this--connecting the Sky-Watcher EQ6R-Pro: Connecting your astro devices without cables

I'm using a VirtualHere server  (

Don at Novaspirit Tech has a great video, walking through the complete setup on the Pi, using Linux on both ends, but it works basically the same with Windows on the client side. ( VirtualHere has servers for just about every OS and hardware combination imaginable, and clients for MacOS, Linux, and Windows. Whatever you're running, it's probably supported. 

UPDATE: I ran an entire night with this setup and ran into an issue about midway through. The virtual USB port inexplicably closed at about the five-hour mark. I have a licensed version installed, so I don't think this is a trial version limitation. I haven't updated the client or server side since I used this setup with the EQ6R-Pro. I reconnected, and everything ran fine after that, but the last thing any of us wants to introduce into the system is unpredictability, so I will have to dig into the cause before trying again.

Posted August 31, 2022

A Long Night of Single-target Hydrogen-alpha Imaging

Five hours of narrowband data right there. This is what 61 x 5-minute exposures will get you through a 3 nanometer Hydrogen-alpha filter--when you algorithmically stack them all together. NGC 7822 is a star forming region in Cepheus, including the emission nebula Cederblad 214, Sharpless 171 and the star cluster Berkeley 59. Apparently this outrageously cool nebula doesn't have a common name, which just doesn't make sense. This should totally be called the Laughing Skull Nebula—or something even better. Missed opportunity right there. Unfortunately, I don't have the authority to make these names... or do I? Okay, while we're at it, see that small squarish cloud structure near the bottom (with two dark eyes and a nose), left of that bright star, which is labeled HR 9094 by the way? That little nebula that looks like it's peeking out of a pocket, is now called the Meerkat of Eternity.

Posted August 30, 2022