Imaging the catseye
Posted: Sun May 16, 2021 11:17 am
Posting this not because it is a great final image but because it is an ongoing project that links quite closely to Brian's thread on narrowband imaging. In addition the catseye poses some interesting challenges of its own but is an attractive object.
Below is 55 min of 66s OSC frames at F 5.0 using a UHC filter and 16 min of 10s OSC frames taken without any filter combined into a single high dynamic range composition.
The high dynamic range approach looks to have worked quite well to solve the problem of the core being so much brighter than the periphery of the nebula. Also at F 5.0 and f 1000 quite a good image could be obtained quickly.
But it also illustrates two problems.
Firstly the HA (+NII?) component of this nebula is weak in comparison with the OIII. The OSC plus UHC filter approach detects both bands OK but with the disadvantage that the ratio of the two is fixed. So improving this RGB image will take adding in some calculated ratio of narrowband both to improve the overall SNR and also to increase the proportion of HA in the image - so narrowband will be a next step when opportunity allows.
The second problem is more intractable though. Generally I like the diffraction spikes that my Newtonian adds to stars - but not so much in the context of imaging a planetary. So this maybe one target where an SCT or refractor is just better?
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SW PDS200, Baader flattener, F 5.0, on a CEM70 Ioptron mount , Pegasus cube focuser, PHD2 guiding using an ASI120MM camera and f = 160mm guide scope
ASI 290MC PRO camera at -10C
Astronomik UHC filter
Frames collected using SC 4 beta version in livestack mode and selected based on FWHM and brightness.
Preprocessing and processing using PixInsight (High dynamic range composition plus HDR masking and stretching)
moonless Bortle 6 skies
55 x 66s frames at gain 124 using a UHC filter, 92 x 10s frames at gain 124 using no filter
Below is 55 min of 66s OSC frames at F 5.0 using a UHC filter and 16 min of 10s OSC frames taken without any filter combined into a single high dynamic range composition.
The high dynamic range approach looks to have worked quite well to solve the problem of the core being so much brighter than the periphery of the nebula. Also at F 5.0 and f 1000 quite a good image could be obtained quickly.
But it also illustrates two problems.
Firstly the HA (+NII?) component of this nebula is weak in comparison with the OIII. The OSC plus UHC filter approach detects both bands OK but with the disadvantage that the ratio of the two is fixed. So improving this RGB image will take adding in some calculated ratio of narrowband both to improve the overall SNR and also to increase the proportion of HA in the image - so narrowband will be a next step when opportunity allows.
The second problem is more intractable though. Generally I like the diffraction spikes that my Newtonian adds to stars - but not so much in the context of imaging a planetary. So this maybe one target where an SCT or refractor is just better?
----------------
SW PDS200, Baader flattener, F 5.0, on a CEM70 Ioptron mount , Pegasus cube focuser, PHD2 guiding using an ASI120MM camera and f = 160mm guide scope
ASI 290MC PRO camera at -10C
Astronomik UHC filter
Frames collected using SC 4 beta version in livestack mode and selected based on FWHM and brightness.
Preprocessing and processing using PixInsight (High dynamic range composition plus HDR masking and stretching)
moonless Bortle 6 skies
55 x 66s frames at gain 124 using a UHC filter, 92 x 10s frames at gain 124 using no filter