Just few points that I thought are needed to be taken.
Testing by using Ronchi grating (or wire mesh) in focus, and looking from a distance is NOT sensitive enough for a visual instrument. For photography, where 15 micron image is excellent, it might be OK, but for a visual instrument it's definetely not good enough. You either need a large flat for autocollimation or larger (good) telescope to provide parallel beam (I used my 8" Newtonian while testing 6" Wright :
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Illuminated slit ==
(Foucault source) knife edge, Ronchi grating
or artificial star or eyepiece
at the focus
> As in the case of the true Schmidt the correction
> if needed should be done on the primary.
This is not a good advice. The correction on primary will be good ONLY for paraxial rays. But in a photographic instrument, we DO care about rays that are inclined several degrees. For oblique rays "projected" zone from the corrector will miss accordingly corrected zone on the mirror and you'll end with twice the problem. In priciple, if the zone is weak, don't worry about it (unless you want really first class visual instrument, in which case it has to be 100% right - that's why I advized against SCT). If zonning is strong - sorry but there is NO other way but to fix the corrector.
> For correctors in SCT's or Wrights which are some percentage of a
> true Schmidt the corrector
In general, correctors for Wright are at least two times stronger than in an equivalent Schmidt. If you fiddle with spacing (by putting the corrector plate closer to the primary to make it easier for secondary to be mounted), it gets even stronger.
I would just add at the end (again) that in my opinion Schmidt and its derivatives are excellent photographic instruments - but for a first class visual use they are just too difficult to make well. Just look at the commercial world : there are plenty of absolutely first class Newtonians, Maksutovs, refractors of all sorts. But noone makes really good SCT (except _maybe_ Takahashi - and for a price !). If you ask a professional optician to make a telescope for you at a given quality level (say, better that 1/8 wave on the front), the SCT would be by far the most expensive of all designs !
Bratislav