Over the past two months I let my scope run on M16 the Eagle Nebula whenever the sky was clear, accumulating some 60 hours of data. Now that so much work has been done I might just share it here. Scope used was a self built 12 inch Truss Newt from a Skywatcher 300F5. ASI2600MM cooled to -15 degrees at gain of 100, Antlia 3nm, 5min subs, OAG guiding with ASI178 bin 2. Mount was CEM60 and ASIair was used for automatic sessions. Processing was done in Deep Sky Stacker and Photoshop.
I had imaged M16 many times before, using Skywatcher Quattro 10, GSO RC10, and self re-built Skywatcher Quattro 300F4, but I never had good results that I liked. This time I was about to finish after getting reasonably good details with some 20 hours or so. But I noticed further improvements with better definitions and lower noises as more data were added, so I went on for many more nights. There was a big issue though. There were only a couple of nights of good seeing when guiding RMS errors would go as low as under 0.2 arcsec for both RA and DEC. I reserved those good nights for Ha, which meant also that stars on Oiii and Sii were overblown and some Photoshop work were needed to minimise those effects. Also many clear skies happened around full in the past two months. I did compare Oiii data collected during full moon and new moon, and there didn't seem to be much differences in details other than overall light casts during full moon which could be readily removed.
A few words about Skywatcher astrograph newtonians. I worked with 3 of these, Quattro 10 in carbon tube, and two re-built 300F4 and 300F5. Quattro 10 was my main scope for many years and it did seem to produce good results as seen by others. Quattro 12/300F4 was the one gave me most headaches until I nailed all problems most recently. However, in diagnosing problems it seemed to me that there might be astigmatism in primary mirrors on both Quattro 10 and Quattro 12, when stars would focus down to short lines perpendicular to each other on either side of focal point. These would result in oblong stars when temperatures changes or if focusing wasn't accurate. I also found that effects of temperature changes were quite similar with Quattro 10 in carbon tube and Quattro 12 with aluminium truss bars, which seem to indicate focus changes were main cause by thermal changes in primary mirrors. On the other hand, 300F5, also using aluminium truss bars, was much more stable with temperature changes, and star donuts would go from rounds all the way to dots on either side of focal point, indicating perfect primary mirror configuration.
Anyway, here is an image with 287, 282, and 155 subs in Ha, Oiii, and Sii, respectively. SHO colours with a bit twist for better looking.
You have some nice data for sure, but if I'm going to be direct I have to say that I find the pallete very strange looking...more like an under water scene than deep space with all the green ...which I suppose isn't that surprising given you put Ha in the green channel. Given that Ha falls naturally in the red spectrum and O111 more in the blue/green colours the look you got isn't surprising.
But, I suspect you know this and you like it, so who can really say what is "real" looking in NB?
However, I'd like to see this image in HSO, or HOO with S blended in as a golden coulour.
Hey John, when it comes to special filters and the like I am not that experienced and as mentioned your image is a little green, however an awesome Photo beautifully taken with the tools at hand, well done. If you like it that is all that matters
Thanks very much for your comments. To be honest I'm not sure what preferred colours M16 should be, and I was trying to minimise colour adjustments for basice colour renditions from combinations of Ha, Oiii, and Sii. I also found that images of M16 were all different on the forum. Mine looked greenish as Ha was far far stronger than Oiii and Sii and it's on the green channel of SHO. Sii was in fact very hard to bring out as it was so much weaker than Ha and Oiii. In stretching Sii I always overblown stars resulting in red fringes on all stars. I was using Photoshop for all processing and I had always wondered how people would do this with PI. Having used Photoshop for so many years with extensive experiences I've resisted trying other imaging software. I'll have another look sometime later. All what I had been focsing on was trying to see how much detalis I could get from the scope and test if woud be up to what 12 inch scopes could do.
and as mentioned your image is a little green, however an awesome Photo 
beautifully taken with the tools at hand, well done. If you like it that is all that matters 
