Hi Ian
I can remember looking into all sorts of designs , the lensless schmidt worked out to be fairly slow and soso quaity.
As you say making a schmidt corrector aint easy , I ended up buying a 10" Meade schmidt newt' and putting in a corrector near the focuser for a much flatter field .
Keep in mind you need to upgrade the focuser and other bits and pieces .
Another thing you can do with the SN's is move the corrector 400 mm futher up and have a spider for the secondary , a bit of a fiddle but will give very good coverage for full frame .
I wound up ditching the idea of using a schmidt and went back to my trusty if a wee bit slow (f/4.66) 10" newtonian and decided I'd go to a 40D at prime focus instead retiring my old Minolta XD5 SLR body from that role .... nice results over the years but film is a bit slow if you want very fine details without lots of grain.
Not too impressed with SCTs and SNT's and MCT's and MNT's from what I've gleened by lots of reading , visiting several astrochat places (just to read threads).
I know SCTs , MCTs, SNT's and MNT's are popular and lots of people have them, horses for courses and what you feel comfortable with.
