Kevin_A For now I am just seeing what 0 Gain and no filter looks like in my bortle 4 as I have not liked the results of my L-Pro filter on broadband targets.
I live in the semi-boonies of Portland, and my skies are dominated by the nearby cities.
North is to the left. East is to the bottom. Southeast (bottom left) is Portland. Souith is Beaverton. NO large cities to the north. Deneb transits at about Zenith (Bortle about 5 to 6), or the center of the image. So, Bortle is direction dependent, and stars with declination south of Zenith are progressively hopeless.
My guess for M45 is that the skies there is about Bortle 6 to 7, and M42 is Bortle 7 to 8. (I swear that when I write my own capture program, that I will add a sky brightness number to the data).
I have taken images of M42 with the Optolong L-ultimate filter last year, and it was a disaster. The filter cuts off a lot of bluer stars, and the Running Man was just a red blob. And there were halos around the brightest stars!
I plan use the Antlia RGB as a wideband filter in place of the IDAS HEUIB-II, which also produces good daylight balanced colors. But the Antlia cuts off more of the sky background.
A Radian Quad still beats the pants out of the Antlia or any Chinese filters, though, when it comes to pure emission nebulas (NGC7000 was not any special with the Antlia).
I just wish Chroma would come out with a wideband RGB filter.
Chen
