M101- dark skies, big fast telescope ~ 3h

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timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

M101- dark skies, big fast telescope ~ 3h

#1

Post by timh »

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?
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aa_M101_VX12_290422_33x70s_plus228x40s_g124_INT_DBE_DBE_COL_SCNR_strmak2_MLT_plus50minHAtored_TRAN_curves_MLT2_affinity16bit_PXbig_MODsmall.jpg (1002.47 KiB) Viewed 620 times
aa2_M101_VX12_290422_33x70s_plus228x40s_g124_INT_DBE_DBE_COL_SCNR_strmak2_MLT_plus50minHAtored_TRAN_curves_MLT2_affinity16bit_PXbig.jpg
aa2_M101_VX12_290422_33x70s_plus228x40s_g124_INT_DBE_DBE_COL_SCNR_strmak2_MLT_plus50minHAtored_TRAN_curves_MLT2_affinity16bit_PXbig.jpg (966.61 KiB) Viewed 630 times
aa2_M101_HA_PXbig.jpg
aa2_M101_HA_PXbig.jpg (993.82 KiB) Viewed 630 times
aaM101_VX12_290422_33x70s_plus228x40s_g124_INT_DBE_DBE_COL_SCNR_strmak2_MLT_TRAN_curves_MLT_affinity16bit_PXbig_blue_small.jpg
aaM101_VX12_290422_33x70s_plus228x40s_g124_INT_DBE_DBE_COL_SCNR_strmak2_MLT_TRAN_curves_MLT_affinity16bit_PXbig_blue_small.jpg (977.09 KiB) Viewed 640 times
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Menno555
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Joined: Mon Apr 20, 2020 2:19 pm
Location: The Netherlands
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Re: M101- dark skies, big fast telescope ~ 3h

#2

Post by Menno555 »

Mmmm, those dark skies really are the best filters :)
Personally I like the 2nd one best. Bit more yellow but more of the arms visible and also more background things.

Menno
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turfpit
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Joined: Mon Feb 13, 2017 8:13 pm
Location: UK
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Re: M101- dark skies, big fast telescope ~ 3h

#3

Post by turfpit »

Second image for me.

Dave
timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

Re: M101- dark skies, big fast telescope ~ 3h

#4

Post by timh »

Thanks Menno and Dave. I will take your advice and go for seeing more of the galaxy over making it look cleaner. I find that the difficult thing about processing is that there is just so much choice that it gets hard to make a decision.

Tim
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