LRGB of the the whale and pup galaxies
Posted: Fri Apr 04, 2025 4:18 pm
Taking advantage of the recent run of clear nights just following the new moon. Same technique as in my previous posts of galaxy pictures. Luminance from a large quality-selected stack (500-1500 frames) of short (10s) highly sampled (0.41 pixel/ arcsec) mono camera images from a large 12 inch F4 telescope was further sharpened using RC Blur Exterminator - and then applied as luminance to an OSC RGB camera image.
A few things that I have learned in applying this technique.
1) It can work well - and even before sharpening - it is possible to get LUM images at FWHM 2 or less under B6 Thames valley skies
2) But it needs a bit of luck. We had about a week or so of moonless nights and high pressure -- but there were only quite short windows of high transparency combined with steady skies.
3) It also requires a lot of imaging because at least half the frames will be discarded during selection
4) (Obviously) far easier with objects that remain close to the zenith
5) It is a technique only really applicable to brighter - or to the brighter parts of - galaxies. Even with a 300 mm mirror darker skies and/or subs longer than 10s (and therefore more blurring) are necessary to get adequate SNR into the luminance of more distant galaxies and faint outer spiral arms etc.
Having said that I think it has worked well for getting this close in image of the whale galaxy - NGC4631 - and its companion. A side on view of an active spiral galaxy the image is very reminiscent of M108. Here 755 x10s of luminance (ASI294MM) was used to inform a 472x40s of OSC (ASI294MC) RGB image. Capture in Sharpcap 4.1 and processing in PixInsight 1.9.
Tim
A few things that I have learned in applying this technique.
1) It can work well - and even before sharpening - it is possible to get LUM images at FWHM 2 or less under B6 Thames valley skies
2) But it needs a bit of luck. We had about a week or so of moonless nights and high pressure -- but there were only quite short windows of high transparency combined with steady skies.
3) It also requires a lot of imaging because at least half the frames will be discarded during selection
4) (Obviously) far easier with objects that remain close to the zenith
5) It is a technique only really applicable to brighter - or to the brighter parts of - galaxies. Even with a 300 mm mirror darker skies and/or subs longer than 10s (and therefore more blurring) are necessary to get adequate SNR into the luminance of more distant galaxies and faint outer spiral arms etc.
Having said that I think it has worked well for getting this close in image of the whale galaxy - NGC4631 - and its companion. A side on view of an active spiral galaxy the image is very reminiscent of M108. Here 755 x10s of luminance (ASI294MM) was used to inform a 472x40s of OSC (ASI294MC) RGB image. Capture in Sharpcap 4.1 and processing in PixInsight 1.9.
Tim
- drizzle_integration_RGB_toSPCC_DBE_registered to LUM_TRAN_LRGB_LUM_EXP_ARCSIN_CURVES_NoiseXt0.3_CROP_affinity_small.jpg (994.89 KiB) Viewed 3166 times