M51 HaLRGB project
Posted: Sun Mar 28, 2021 6:26 pm
I am embarking on an HaLRGB capture of M51. I thought I would share my experiences as the project evolves. This will be my first serious attempt at guiding using PHD2.
The intention is to capture L @ 100s, RGB @ 300s and Ha @ 600s. The finish will hopefully produce an image with 4 hours of integration time. The first phase was to try out the equipment with guided 300s exposures. The night chosen had thin/intermittent cloud so nothing would be lost if difficulties were encountered. This is the result of a 12x300s imaging session.
Before commencing the image run, a single frame was captured and analysed in FITS Liberator.
Note that the linear histogram has clearance of 11,000 at the left hand side (no faint data lost) and the histogram does not touch the right hand side (no over exposed data). As a check a stretch using the function ArcSinh(ArcSinh(x)) was applied to the data. A healthy looking histogram (classic shape for a deep sky object) suggested the settings were good for a data run. See above image for results.
The capture plan was devised using @oopfan's (thanks Brian) SNR calculator.
The tool allows for RGB white balance using number of frames rather than torturing the resultant stacks in some astro-imaging software (which can result in loss of colour and increased noise). This work can be attributed to Al Kelly's article White Balancing RGB Filters with a G2V Starhttp://www.kellysky.net/White%20Balanci ... ilters.pdf . The way the Atik 314E and my filters behave with red, I need twice as many red as green frames to achieve colour balance.
Also note that the SNR for each of the RGB stacks is roughly equal which will avoid saturation of stars in a particular colour. The L and R+G+B SNR are roughly equal as most of the detail will come from the Luminance frames.
I summary the project will entail captures as follows:
L: 40x100s
R: 8x300s
G: 4x300s
B: 7x300s
Ha: 6x600s
bias frames 50
flat frames 50 for each filter
dark frames 20 for each exposure
I will probably capture 2 or 3 extra RGB frames to allow for planes, satellites and meteors.
The darks are 20x600s, 20x300s, 20x100s which totals ~5.5 hours. Tonight is cloudy but the darks are being collected with the scope and camera on a bench in the greenhouse. I will forgo temperature matching perfection for this project.
There are a couple of imaging opportunities over the next week albeit with a full moon around.
This is the result of the trial run last week (best 11 of 12 frames, stacked in APP, black point adjusted in GIMP and denoised in NEAT) :
I will add to this thread as the project evolves.
Looking at Canes Venatici there are some interesting objects to capture over the next month or so. All except the M3 globular cluster will probably work with the above exposure settings.
Dave
The intention is to capture L @ 100s, RGB @ 300s and Ha @ 600s. The finish will hopefully produce an image with 4 hours of integration time. The first phase was to try out the equipment with guided 300s exposures. The night chosen had thin/intermittent cloud so nothing would be lost if difficulties were encountered. This is the result of a 12x300s imaging session.
Before commencing the image run, a single frame was captured and analysed in FITS Liberator.
Note that the linear histogram has clearance of 11,000 at the left hand side (no faint data lost) and the histogram does not touch the right hand side (no over exposed data). As a check a stretch using the function ArcSinh(ArcSinh(x)) was applied to the data. A healthy looking histogram (classic shape for a deep sky object) suggested the settings were good for a data run. See above image for results.
The capture plan was devised using @oopfan's (thanks Brian) SNR calculator.
The tool allows for RGB white balance using number of frames rather than torturing the resultant stacks in some astro-imaging software (which can result in loss of colour and increased noise). This work can be attributed to Al Kelly's article White Balancing RGB Filters with a G2V Starhttp://www.kellysky.net/White%20Balanci ... ilters.pdf . The way the Atik 314E and my filters behave with red, I need twice as many red as green frames to achieve colour balance.
Also note that the SNR for each of the RGB stacks is roughly equal which will avoid saturation of stars in a particular colour. The L and R+G+B SNR are roughly equal as most of the detail will come from the Luminance frames.
I summary the project will entail captures as follows:
L: 40x100s
R: 8x300s
G: 4x300s
B: 7x300s
Ha: 6x600s
bias frames 50
flat frames 50 for each filter
dark frames 20 for each exposure
I will probably capture 2 or 3 extra RGB frames to allow for planes, satellites and meteors.
The darks are 20x600s, 20x300s, 20x100s which totals ~5.5 hours. Tonight is cloudy but the darks are being collected with the scope and camera on a bench in the greenhouse. I will forgo temperature matching perfection for this project.
There are a couple of imaging opportunities over the next week albeit with a full moon around.
This is the result of the trial run last week (best 11 of 12 frames, stacked in APP, black point adjusted in GIMP and denoised in NEAT) :
I will add to this thread as the project evolves.
Looking at Canes Venatici there are some interesting objects to capture over the next month or so. All except the M3 globular cluster will probably work with the above exposure settings.
Dave