Orion Short Tube 80 Test

11/16/2025 - One cloud free and moon free night before clouds & rain set in... had cleaned the venerable Meade LX10 8" SCT OTA, corrector, primary and secondary mirror (after a very dark disturbance arrived for two evenings' collection)...and awaiting replacing the steel screws with stainless...so brought up the Orion ST-80 for testing.

Worked to attach the Xagyl filter wheel and Svbony Sv405cc camera. Noted the correct back focus for the Hotech SCA flattener is 55mm with 6.5mm between the Sv405cc chip and housing...leaving 48.5mm of back focus distance to work with. Used extension tubes to get as close as practical... and mounted the ST-80 on the CGEM DX with the Cosmicar 25mm F1.8 CCTV lens set up for guiding using the Zwo ASI120-MC.  Focused manually successfully (tested within the focus tab within Ekos).  

After focusing, found that the Hotech SCA back focus is not perfect...with coma visible on the extreme edges...extending for nearly 1/5 of the size of the frame all around (although not symmetrically...results were worse at the top...and the top left in particular). Given limited time, left this as-is for now...but future work is needed to optimize this (assuming Xagyl filter wheel continues to make sense for this OTA).  Noted that the Align tab is super fast using the UV/IR filter instead of the dual narrow band filter, for example.

Within the Ekos Align tab, noted the FOV for the ST-80 in this configuration (400mm, F5, no reducer or barlow) is: 164.9' x 112.3'. Which may nearly contain the entire NGC 1499 nebula.

Did not double-check the polar alignment...although oddly noted that without guiding enabled...test shots up to 120s showed no symmetry...suggesting...very good polar alignment.

Did a final focus adjust for the dual narrow band filter...and crafted a sequence in the Ekos CCD tab for 20x80s light frames at gain 285, offset 24 with the camera set to 0C...then generated a new schedule for NGC 1499 to run through 05:30 tomorrow.  After launching this, the plate solving went well...but guiding failed.  Stopped the scheduler and forced the internal guider to clear old calibration data. After restarting guiding, the calibration succeeded....and guiding was closer to normal.

By 23:37, the Indi Allsky backyard camera showed a pseudo sky quality metric of ~4700...which is reasonably good.   The Weewx outdoor weather station showed the following:

        "time": "2025-11-16T23:35:00-0500",

       "generator": "weewx 5.2.0"

        "temperature": {"value": 40.881481481481465, "units": "°F"},

        "dewpoint": {"value": 22.4086210738118, "units": "°F"},

        "humidity": {"value": 47.370370370370374, "units": "%"},

        "heat index": {"value": 36.89603703703704, "units": "°F"},

        "wind speed": {"value": 0.0, "units": "mph"},

        "wind gust": {"value": 0.0, "units": "mph"},

        "wind chill": {"value": 40.881481481481465, "units": "°F"}


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