Phil,
It is a level adjust, this link may help:
http://www.middlehillobservatory.co....d%20curves.htm
That link is working on mono images. For us DSLR imagers it is the same process except we need to shift the levels of each RGB channel individually for best results.
In PS, Ctrl+L will bring up the adjust dialog, then the drop down dialog will allow you to select each channel, see attached where I have already adjusted the Red channel.
You have some good data. I have been thinking about buying a Mak-Newt.