Bode's Galaxy (M81) and The Starburst Galaxy (M82) - 2023-11-19 - Starless Ha Test Image
This Ha-only image is probably a little soft. It was captured while testing filter offset focusing. I found that offset focusing does not work well going from my wideband filters, which vary by just a few focuser steps from one wideband filter to the next, to my Ha (narrowband) filter that differs by 50 to 60 focuser steps.
The reason for this is that my optical configration has the main camera behind the filters, and the guide camera is before the filters. If the main and guide cameras are perfectly co-focused behind one of the wideband filters, there is no problem switching to another wideband filter that is offset by just a few focuser position steps, because moving the main camera into focus after the filter change does not move the guide camera enough out of focus to affect guiding.
If the switch is from a wideband filter to the Ha filter, then the 50-step movement moves the guide camera enough out of focus to seriously degrade guiding.
What I learned from this test is that a manual refocus of the main and guide cameras is necessary when changing between narrowband and wideband filters. Better to learn while testing at home than to find out the day after returning from a dark sky site.
ZWO ASI6200MM-P/EFW 2" x 7 (Ha)
Tele Vue NP101is/LFC
Losmandy G11
Captured in NINA (20 subs x 420s with Ha filter for 02:20 total integration time.)
Processed in PixInsight
Bode's Galaxy (M81) and The Starburst Galaxy (M82) - 2023-11-19 - Starless Ha Test Image
This Ha-only image is probably a little soft. It was captured while testing filter offset focusing. I found that offset focusing does not work well going from my wideband filters, which vary by just a few focuser steps from one wideband filter to the next, to my Ha (narrowband) filter that differs by 50 to 60 focuser steps.
The reason for this is that my optical configration has the main camera behind the filters, and the guide camera is before the filters. If the main and guide cameras are perfectly co-focused behind one of the wideband filters, there is no problem switching to another wideband filter that is offset by just a few focuser position steps, because moving the main camera into focus after the filter change does not move the guide camera enough out of focus to affect guiding.
If the switch is from a wideband filter to the Ha filter, then the 50-step movement moves the guide camera enough out of focus to seriously degrade guiding.
What I learned from this test is that a manual refocus of the main and guide cameras is necessary when changing between narrowband and wideband filters. Better to learn while testing at home than to find out the day after returning from a dark sky site.
ZWO ASI6200MM-P/EFW 2" x 7 (Ha)
Tele Vue NP101is/LFC
Losmandy G11
Captured in NINA (20 subs x 420s with Ha filter for 02:20 total integration time.)
Processed in PixInsight