So I ended up with this. Had a few interesting accidents (my S2 frames weren't centred and O3 was a disaster with reflections), but salvaged something. Kind of happy with the weird colour. Still aiming to do some regular RGB but the skies aren't obliging. Ended up with roughly 10.5 hours of combined Ha, O3 and S2 using an ASI1600MM-Pro, my ED80 and a HEQ5 Pro. Processed in Pixinsight as a SHO image but with the green removed.
Astrobin: https://www.astrobin.com/379512/
Ben, every ASI1600MM owner has problems with Alnitak reflections when shooting this area. There are some threads on CN about it. The reflection is caused by the mono sensor surface reflecting back into the sensor cover glass (note I am not talking about the camera AR window). Panasonic make these sensors for ZWO, and when they produce a mono sensor without the Bayer matrix, the surface is more reflective than a normal OSC surface. Panasonic use their normal sensor cover glass on these mono sensors, which are not anti-reflective. So that is something we have to live with, and short of trying to change the sensor cover glass (with say some Astronomik MC-clear AR glass, which in all likelihood would destroy the chip), there is nothing that can be done other than exposure management or framing to avoid Alnitak.
ZWO are aware of the issue, but Panasonic has been unwilling to produce these sensors using different cover glass, which us understandable given the small batch size ZWO buys and the impacts on production runs of changing glass used. Of course it may just be a matter of cost.
Some folks claim it is the filters used that contribute to the problem, but I see your using Astrodon filters so that can not be an issue in this case.
Thanks Geoff and Glen. I’ve read up on the ASI1600 reflection issues (especially around Alnitak) and figure I’ll just have to live with it. There were reflections in all the stacked subs but O3 was remarkable!
With Alnitak cropped and field limited with some appreciation of Andy’s previous comments re balancing the FOV. Horsehead seems kind of lonely like this though.
Cool colours & framing Ben, a bold presentation that looks good!
Maybe worth cropping a bit off the bottom third of the frame to balance the image?
Well persevered
Thanks JA and Andy. Maybe something like this Andy? Also deals with some of the noise I guess.
That cropped version looks good Ben. The "Veil Wall" behind the Horsehead is well done. Your working with false colour representaion, so artistically it can be whatever you choose - there is no right way. That is a keeper.
Thanks Mike and Glen. Freedom to do what you want can be a good thing but it is nice to have thoughtful comments on this forum from those more experienced. Much appreciated :-)
I haven't run into those weird reflections with my ASI1600 yet but it's probably just a matter of time. I have a few thoughts about how you could reduce the effect in processing...
Thanks Rick, Martin and Andy. I’ve sent you a PM Rick for more info :-) Apparently, from my forum browsing, Alnitak is the ASI1600MM’s worst enemy, especially in O3.
As for your reflections (or lack there of) Rick, it doesn’t show up in lens’ as much which is what I believe you’ve mostly used so far.
I just had a close look at my Ha image of the area using the Borg 55FL (200mm focal length) and there's possibly a trace of a circular halo but that's all. Shame I didn't get a chance to do any Oiii...
