Hi everybody,
Here is M16 and M17, a little less than 2 hours total exposure. 14x8m and 9x10s. Imaged with a Takahashi FSQ 106ED and a Hutech modded Canon 6D, from Allumette Island, Quebec, on July 3, 2016. It took me a while during processing to realize that the slight haziness of much of the image is likely ionized oxygen, as there seems to none visible on the left side of the image where the wall of dust is blocking the light from the Eagle nebula. You can see what I assume is the ionized O2 most clearly on the lower edge of the Omega nebula on the right side of the image. M16 M17 (headdown) - Full resolution | AstroBin If you click on the image at the Astrobin link, it will show you a smaller version where this haze is easier to see.
Dean
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Really nice Dean. I like these wide field views. To be honest though, I think the haze you speak of looks like standard gradient across the image. I doubt that O2 would show up that well in an OSC image because the background would overwhelm the weak O2 signal. Still, a great image and processed very well.
Thanks Joel,
I don’t think that is gradient, because there shouldn’t really be any. It was imaged from a dark site with an 88mm image circle. I used flats, so it would be surprising to have any gradients left. And I hadn’t noticed any gradients in the original subs. The left side of the image is clear where it is in the shadow of a dust lane of the Eagle nebula, which leads me to believe it is either ionized O2 or perhaps reflected dust? And it also seems to be the same colour as the dust? O2? at the bottom edge of the Omega nebula, leading me to believe that it is of the same stuff. You can also see traces of it in this image, around the Lagoon nebula.
Dean
I don’t want to take anything away from the image, it’s great! And I could certainly be wrong.
There certainly is OIII in M17 and M16. It’s just that the haze in the background area is much too strong, IMHO, to be OIII. In your excellent Lagoon image the O2 is clearly present around the nebula, but not really in the background. The M16-M17 image OTOH has that haze extending across nearly the whole image in a rather linear way. This DSLR image of the same area from the dark skies of Namibia does show some O2 in the background, but it is not nearly as strong or as linear as in your image.
I probably shouldn’t have said anything, because it really is irrelevant. If you are happy with the image, and you should be, then my comment was pointless. 
Not at all Joel,
I take no offence at your questioning what the haze is, as I am still trying to figure it out myself and and am quite curious. Discussing it can help clarify what it could or could not be, and I don’t mind at all.
The image you linked to is imaged using a lot older Canon than the 6D, and it was imaged at 400 ISO, as opposed to my Takahashi image with the modded 6D at 1600 ISO. (edit: my error, not an older Canon but a new Nikon, but still at only 400 ISO) Those factors together are going to make a huge difference in what the respective images can show, even if that one was from a darker site than mine. And then there is processing. This is an HDR image, processed carefully in Pixinsight, as well as my admittedly limited abilities allow. 
So I think it is hard to compare the two. Though here is a link comparing the two cameras that I just found. I’m happy we have 6Ds.
To me the haze seems to be the very same shade of blue as you can see concentrated on the bottom of the Omega nebula. This is the strongest evidence to me that it is a fainter layer of the same stuff…whatever that is!
And there just should not be any gradient in this image, as it was taken from a dark site, with a Tak, and flats were used. All of those together lead me to believe that it is not a processing artifact or gradient. If not sooner, the mystery will be solved within about a year. I am retiring in a week, and will soon be putting ridiculous amounts of time on targets, including this one. Whatever it is or is not will be shown eventually!
Dean