M27 and filters: It's the colors, Dumbbell!
More experimenting now that I have a functional mount and a place to leave the Sweet 16 set up. Love it!
These are some test images of the Dumbbell, with and without the 0.75 focal reducer/field flattener that Optec makes just for the Meade 16" non-ACF SCT. Unfortunately, or maybe not, it has no provision for a filter, so the first is with the Nikon D810A alone. I'm surprised by how different it turned out from the filtered images with no FF. The colors are not constrained to what can be formed from blending Ha red and OIII blue-green, and I think look more natural. And so many more stars! I suppose this is an effect of not losing 90+% of stars' light to a narrowband filter.
Meade 16” SCT w/Optec TC/FF, 1600GTO mount, Nikon D810A full-frame DSLR. Stack of 60 x 60s, unguided, Bortle 7, processed in PS and DeNoise. For overall quality, there's no question that the unfiltered file has the others beat.
Some of the differences between images is due to my ad-hoc and non-systematic approach to processing. I hope this will improve when I migrate to Pixinsight! But not all the difference; the two filtered images have much noisier, mottled backgrounds. I think it has to do with the fact that in the two filtered images, the lack of sky/light pollution background allowed me to squeeze the data harder to bring out fainter nebulosity. The two filtered images go deeper, but at the price of amplifying noise. Looking forward to 10x the integration time with the cooled camera!
FF/TC, no filter
L-eNhance filter, no FF/TC
L-eXtreme filter, no FF/TC