M101- dark skies, big fast telescope ~ 3h
Posted: Sun May 08, 2022 3:00 pm
Managed to set up and use the 12 inch VX12 on a dark sky site on a farm in Norfolk. Only got about 35 min of frames but very good and combined with some also obtained from a darker sky site in Dorset the previous year using an 8 inch Newt (PDS200).
This AS1294 MC OSC camera image combines Bortle 4 frames (70 x 40s and 33 x 70s) taken from dark(er) locations using the 8 inch F 5.0 or 12 inch F 4.0 Newtonian respectively - these were also combined with 158 x 40s Bortle 6 frames. Total imaging time was about 3h with about half at Bortle 6 and the other half at Bortle 4. Only UV/vis cut filter. The frames were all integrated together using SNR weighting (PI) - the final image was therefore dominated by the dark site frames.
A 17 x 3 min HA (7nm filter) image was also taken using an AS1294 MM mono camera.
This year's set up was a VX12 Orion Optics (UK) Newtonian (f = 1200mm, F4.0), SW parracor type coma corrector, CEM70 Ioptron mount, Baader steeltrack focuser, Pegasus Cube2 focus controller, PHD2 guiding using an ASI 120 mm guide camera and 80 mm SW startravel refractor at f = 400 mm. Lat year's was similar but with a PDS200 main and 8x50 mm guide scope.
Processing was as normal in PI - The HA -supplemented version of the image which highlights the galaxy's HA regions was obtained by adding a small part of the HA-RED subtracted image (shown) into the RGB red channel. It is quite tricky to get this subtraction right and to avoid artifacts-- the idea is to subtract red channel signal from the HA image until the stars about cancel out - however star sizes often don't quite match or exactly subtract and so some manual intervention to remove star remnants is required - otherwise theses appear as spurious spots of HA.
It is a bit of a slog getting the 12 inch scope out to dark sites and then a matter of luck whether the skies will be kind but rewarding when it works! I am seeing a lot more extent to this galaxy at B4 than at B6...although sometimes the price for more transparent dark skies seems to be higher FWHMs. I notice that Menno''s take on the same subject is less extensive but sharper and less stretched.
Tim
PS. With objects like this I find it difficult to know what 'best processing' is. I added a second version - a bit less stretched - and lifting the blue a bit. Would appreciate any comments on which would be better to put up on Astrobin?
This AS1294 MC OSC camera image combines Bortle 4 frames (70 x 40s and 33 x 70s) taken from dark(er) locations using the 8 inch F 5.0 or 12 inch F 4.0 Newtonian respectively - these were also combined with 158 x 40s Bortle 6 frames. Total imaging time was about 3h with about half at Bortle 6 and the other half at Bortle 4. Only UV/vis cut filter. The frames were all integrated together using SNR weighting (PI) - the final image was therefore dominated by the dark site frames.
A 17 x 3 min HA (7nm filter) image was also taken using an AS1294 MM mono camera.
This year's set up was a VX12 Orion Optics (UK) Newtonian (f = 1200mm, F4.0), SW parracor type coma corrector, CEM70 Ioptron mount, Baader steeltrack focuser, Pegasus Cube2 focus controller, PHD2 guiding using an ASI 120 mm guide camera and 80 mm SW startravel refractor at f = 400 mm. Lat year's was similar but with a PDS200 main and 8x50 mm guide scope.
Processing was as normal in PI - The HA -supplemented version of the image which highlights the galaxy's HA regions was obtained by adding a small part of the HA-RED subtracted image (shown) into the RGB red channel. It is quite tricky to get this subtraction right and to avoid artifacts-- the idea is to subtract red channel signal from the HA image until the stars about cancel out - however star sizes often don't quite match or exactly subtract and so some manual intervention to remove star remnants is required - otherwise theses appear as spurious spots of HA.
It is a bit of a slog getting the 12 inch scope out to dark sites and then a matter of luck whether the skies will be kind but rewarding when it works! I am seeing a lot more extent to this galaxy at B4 than at B6...although sometimes the price for more transparent dark skies seems to be higher FWHMs. I notice that Menno''s take on the same subject is less extensive but sharper and less stretched.
Tim
PS. With objects like this I find it difficult to know what 'best processing' is. I added a second version - a bit less stretched - and lifting the blue a bit. Would appreciate any comments on which would be better to put up on Astrobin?
