Yesterday I tried to experiment with my new mono camera and the LRGB filters to gather some experience with the new equipment. My current experience allowed me to capture some nice (in my opinion) DSO pictures with my stock DSLR and William Optics refractor. On the other hand, I have the new camera and also an Meade 8" ACF that I would like to work with. With my post, I'd like to get some feedback on where I'm likely on the right track and where I am wrong.
Scope: Meade 8" ACF f/10 with reducer, yielding an f/6,3.
Camera: fan cooled Altair Hypercam 183M (mono) with pixel size 2,4um.
Guiding: Guide scope. Guiding itself went perfect, star quality on the subs is very good.
My target was M81 (Bode's galaxy) as I had just made images of M37 under the bright moon (follow the AstroBin link in my signature). My goal was to capture before the moon rises high above the horizon and use the dark sky.
I took 84 L subs with 30 seconds exposure. The RGBs have each 64 subs also at 30 seconds. For all filters, I used 2x2 binning.
Here's a list of questions:
1. I've read people take L subs with low binning, even down to 1x1 and RGB at 2x2 or 3x3. With the optics above, a 1x1 binning would have given me 0.4"/pixel. Hence, I didn't see a need to capture L and RGB at different binning. What's your opinion or suggestion here?
2. I'm not sure about the exposure times. With the DSLR I took the approach to try to expose as much as possible until the first stars start to saturate, given that the histogram "peak" is quite a bit above the dark noise. I tried doing the same with the mono (12-bit btw. vs. 14-bit on DSLR). The largest stars just saturated a bit and the histogram mean was just above the darks mean. In post processing, it looks to me that I have to stretch too much to start to see details and then the noise comes out. I guess I'd need to expose longer or capture more subs?
3. The moon: I started at around 7:30pm. At my place it's just about to get "astronomically" dark. However, I can see on my L subs that mean intensity decreases over time. The R and G have a constant mean. When the moon was about to get above horizon, I can see how the mean intensity of the B subs starts to increase. When I try to compose RGB, the resulting image has a rather strong blue tone. I would attribute this to the moon?
4. To compose RGB, I used Affinity Photo. To adjust for the different sensor QE, I am adjusting the brightness of the R and B channel. The result seems to give a rather good color. Your opinion on this procedure?
You can see, I have quite some questions. If somebody likes, I can provide the stacked images for each channel so that you could take a look and maybe give a recommendation on which knob I should turn most.
Edited by barnold84, 03 March 2021 - 12:01 PM.