Another Rocking image Bob!!! You are DSLR wizard!!!!
My guess is that, at 600sec @ ISO 1600, that histogram was moved pretty far to the right at f 4.5!!!!
Bob, Do you have the IS version of the NP101 or the regular version?
I am looking at the either a used NP101 or new SV105. But the SV105 is limited to f7 considering that there
is no proven focal reducer for it at this point to take it below f7. (Maybe the Riccardi reducer sold by APM for $700, but I have yet to
see someone use the APM reducer with the SV105). Anyway, my concern is that the SV105 just will not grab enough
light at F7 for my DSLR vs. the NP101. Still, I would probably prefer the SV105 for general observing.