Got sick of waiting for some clear nights to finish my M16 narrowband test. I have gone ahead with the little data i have available and created a bi-colour image (Ha 6x300" and Oiii 10x300"). They are far enough apart on the spectrum to test for any issues caused by slightly different focal lengths, which i think the rear corrector manages to sort out. That was my testing intent, to see if they register and stack without fringe offset, and i think it looks ok.
I have a concern about what appears to be a few vertical diffraction spikes on some brightest stars but it maybe that i left a focus mask on during one sub and that could cause it. I have to go through the subs individually to check for focus mask diffraction.
The main issue is still field curvature, and my attempts to flatten it with a Hotech fast refractor flattener failed, actually made the situation much worse. Given the design, with the rear corrector, i may not be able to flatten the field. So cropping seems to be the inevitable solution on this scope; and frankly to be expected in that it is optically designed for visual use.
I have posted the image to my Astrobin gallery, see the link below.
Don't expect a masterpiece, its a test image, and it is cropped.
Comments welcome as long as you don't suggest buying an APO.
http://www.astrobin.com/261164/