Testing a Dark Filter in the New Year

 01/28/2026 -- bad skies, cold temperatures... so far only a few opportunities for imaging in December of '25 and January (so far) in '26... and tonight is not really much better. Giant moon, poor-ish skies... but took the opportunity to finally pull off the covers and test out a new totally dark filter (black) from Svbony that may aid in collecting dark and bias calibration frames at the end of a session.

Installed the new black filter in the Xagyl 8-position filter wheel (now with position 1 == UV/IR, position 2 == dual narrow band (Ha/OIII) and finally position 3 == black).

The Indi allsky backyard camera pseudo sky quality metric is grim (even in "moon mode") with a value over 37k at 22:31.  Save a copy of the outdoor weather station JSON report at 22:20 and noted lovely conditions (to include light wind):

"time": "2026-01-28T22:20:00-0500",
"generator": "weewx 5.2.0"
"temperature": {"value": 19.79032258064517, "units": "°F"},
"dewpoint": {"value": 3.1927927908374607, "units": "°F"},
"humidity": {"value": 47.74193548387097, "units": "%"},
"heat index": {"value": 19.79032258064517, "units": "°F"},
"wind speed": {"value": 2.2903225806451615, "units": "mph"},
"wind gust": {"value": 5.0, "units": "mph"},



Seeing forecast for 01/28-29/2026 from Clearoutside and metoblue (bottom) suggesting light clouds at low and mid altitudes and poor seeing conditions.

Struggled initially to get the OTA into focus using the Ekos focus tab with the Meade Zero-shift focuser because it appeared to reach a limit in moving outward (cables?) and after initial improvement...would not move further. Ultimately switched to adjusting the main mirror focus knob manually with the Meade Zeroshift micro-focus set in a mid-position ... since it stopped correcting with HFR's of near 5.6 (attempting to send it out further didn't improve results).  Manually turning the main mirror adjustment to the right by 1/2 turn (right) fixed the focus issue manually...allowing the Meade Zeroshift and Ekos autofocus to adjust fine focus.

Next, ran the PHD2 drift alignment tool. Initial error of -16.41' (pre-meridian flip) was surprisingly small (given a couple months unadjusted on the deck).  Adjusted by turning the azimuth dial to the left several notches. Bad juju.  Resulted in -41.3'.  Adjusted by turning the azimuth dial to the right...resulting in a remarkable 0.60' error after two adjustments.

With the large moon, wanted a suitable deep sky narrow band target (nebula), but none were in view... sadly... And so for testing purposes only set up the scheduler for M106 and then M51 with 20x80s UV/IR followed by 20x120s dual narrow band.  Added a third M51 task in the scheduler using a sequence file with 20x80s and 20x120s and 20x0.000036s for dark and bias collection attempt with the new filter.  Set the sequence capture type to 'dark' and 'bias' respectively...although this may force collection to stop to confirm the configuration (tbd).

Ultimately, 57x120s dual narrow band light frames were collected along with 60x80s UV/IR light frames. Additionally, starting ~08:00, 20x120s and 20x80s dark frames and 20x bias frames were collected with the new Black filter (since the scheduler task did not have a chance to run).

Ekos Analyze tab for collection between 01/28-29/2026 showing execution of a single scheduler task - M106 - from midnight past 04:00. Low and remarkably stable guide errors between 1 and 2" RMS with relatively few failed collections. Metrics including sky background vary between collection using the UV/IR vs dual narrow band filter...but skies generally appear to improve slightly after 03:30.



Indi Allsky backyard camera metrics for 01/28-29/2026 illustrating relatively poor pseudo sky quality numbers (even in moon mode). When the moon did set after 04:00, the non-moon mode pseudo sky quality metric remained above 10,000 (exceptionally poor skies). This is also reflected in low star counts over night.  A bank of clouds passed overhead betweeen 02:50 and 03:30.


Weewx outdoor weather station measurements for 01/28-29/2026 showing very cold temperatures (below 10F) and no wind or gusts during collection between mid-night and 04:00.

PHD2 guiding session RA (blue) and DEC (red) errors during one of several guiding sessions during collection on 01/28-29/2026 for the M106 job. Dither events are called out. DEC errors seem better controlled during stable guiding periods than RA.

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