I am sorry, but you have that backwards.admin wrote: ↑Tue Oct 26, 2021 4:28 amThat's not how that works though?I don't believe that this is strictly true.
My camera, ASI533MC Pro for example, is sensitive to Ha signal in its green/blue pixels. So even if L-Extreme filter was used, the O3 signal in the green/blue pixels would still contain a chunk of Ha.
From the graph above,
the response of green/blue pixels to O3 at 500nm is 0.92/0.51
the response of green/blue pixels to Ha at 656nm is 0.16/0.05.
So, green/blue pixels will contain (0.16+0.05)/(0.16+0.05+0.92+0.51) = 12.8% of Ha signal.
And since Ha is usually much stronger than O3... well, hence the fake HOO.
The response of the blue + green channels @ 500nm is (0.5 + 0.9 = 1.4), with Ha at that line being ~0.04.
This yields (0.04 / 1.4) * 100% = 2.9% Ha "contamination" in the aggregate O-III signal. That is virtually negligible.
The response in the blue + green channel @656 is (0.16+0.05 = 0.21), with Ha at that line being ~0.8.
This yields (0.21 / 0.8) * 100% = 26.25% O-III "contamination" in the red channel. That is much more significant.
Given that we know what the (almost) pure O-III looks like, we can subtract 26.25% times the O-III signal from the Ha signal at every pixel and arrive at the original Ha signal. That's what the Wipe + Color module combo does, as color is determined by relative differences after subtraction of a constant (by Wipe).
For luminance, the contamination too is not a problem (unless you are trying to isolate purely the Ha of course, like is the case with the moon example cited above, in which case a measure of the O-III needs to be subtracted for this particular camera). For luminance, you would add all signal you have collected together anyway to achieve the best SNR.
"Ha "contamination" in the aggregate O-III signal" is
"The response in the blue + green channel @656"
not
"The response of the blue + green channels @ 500nm."
Also, I don't quite understand the point about " the Wipe + Color module combo." How do they know what camera I have to calculate the pure O3 signal from the nearly pure Ha (assuming that my response immediately above is correct?)
P.S. Sorry about calling the O-III spectral line O3. I know O3 is ozone, it's just easier to type.
Just to prove that I am not an actual dummy but an ozone expert, here's one of my most cited publications about ozone chemistry.
https://onlinelibrary.wiley.com/doi/abs ... .200502686