I haven't done this yet, but I was considering getting a large gray photographic white balance card and taking a shot at various settings to see what the histogram looks like when the data is absolutely neutral and the histogram peaks SHOULD be aligned. Then I can make note of the adjustments I need to make to compensate for the filter and such and just apply those... seems like that would be objectively correct no matter what.
Jerry Lodriguss (award winning photographer as well as award winning astrophotographer) says you should set color balance both with and without filters during the day using a digital grey card. IE develop Custom white balance / color balance settings for no filter, camera + filter A, camera + filter B, etc. At night set WB to the custom one applicable for whatever is in the image train .... camera + no filter, camera + A, etc. Then away you go, start imaging. NOTE you will still have to slightly tweak the WB as you move for object to object. The CWB is a GREAT starting point and greatly speeds up getting a good EAA experience, but obviously in different parts of the sky with different LP, dust, colors of the object you will still have to make slight tweaking.
You only have to develop the table once. You don't do this every day you decide to head out.
I'll put how to do it with DSLR and with ZWO astro cam. First the DSLR ...
His advice works perfectly for my DSLR's. Set the ISO you are going to use at night, then set AV and shoot the grey card. Set that image taken as a Custom White Balance (CWB) within the camera. Put on filter A and repeat ending up with an image stored on your SD card for use as a CWB within the camera for no filter, filter A, filter B and so on. At night just select which image for that particular filter applies and set it as the CWB to use. Done!
Now two methods with ZWO's ...
For my ZWO's, set the typical gain you are going to use at night, point at the grey card and select Auto for the whitebalance in sharpcap and then note where the RGB (or RB) sliders values automatically adjust to. NOTE this is NOT stacked frames (no stars to stack!) but just the single shot image preview window and its histogram. Then add filter A and so on resulting in a table of RGB / RB values for camera + filter A, and so on. At night, set the RGB / RB sliders so the value in sharpcap is as per what you noted down in the digital greyscale tests and start imaging. Add filter A, set those values and so on.
But, I have found it not so good for my ZWO's. Why? I think the auto WB in SharpCap may not quite get it right when it see's a solid grey image on the view window? Or maybe its my old version of SC? However, it may work for you so I suggest trying your ZWO first with the method above. If it works for you then away you go. If, like me it doesnt work so well for the ZWO, then try my method two down below.
For my ZWO's (again you dont have to do this everytime you go out ... just pick a day when you are bored and shoot a whole bunch of CWB settings and note them down). I setup in the daytime around an hour before sunset, and point the scope and camera at a typical imaging gain at a distant scene in the North or South (IE away from setting Sun bright West and away from highly illuminated stuff over in the East). The scene should preferably contain bits of blue sky, green grass, red roof of a house or if no red maybe a brown tree trunk, brown bricks .... etc ... get the drift .... something on the horizon way down the street etc with some B G and Red/brown. Without stacking - using just the single preview screen in sharpcap - click on the Auto WB checkbox in SC.. If the Auto setting looks fine then note down the RGB / RB values and use them. If the auto looks bad, then adjust RGB / RB until the blue sky, green stuff, red / brown stuff looks about as natural color balanced as you can see with eyeballs out the window/down the street. Then note down the RGB numbers for that setting. Then I stick on filter A and do the same.
As earlier, then at night, set the RGB / RB sliders so the value in sharpcap is as per what you noted down in the down-the-road-scenery tests and start imaging. Add filter A, set those values and so on.
Again, they are very good and quick starting points, you will still have to make slight tweaks as you slew all over the sky and to different objects.
Edited by Howie1, 20 November 2019 - 09:26 PM.