> Suppose we take a short focus primary (eg f.3) and mount a barlow lens/coma
> corrector (designed for the purpose) on a small diagonal close inside the
> primary focus
Have you ever tried to make an f/3 mirror to a "planetary telescope" standard ?
We can all contemplate, and theorize to our hart's content. I can give you some fantasticly corrected high performance designs that are so difficult to execute that NOBODY to date has made a single prototype. The key factor here (in my opinion) is "can we make it ?" At last, this is Amateur Telescope MAKING group.
> One could also consider an all reflecting version. If one tilts the
> secondary of a cassegrain (or preferably a Ritchey-Chretien) through, say,
> 30 degrees the eyepiece can be positioned in the side of the tube. I'd call
> this a "Tilted Secondary Ritchey Chretien". This reduces the secondary to
> focal plane distance (allowing a smaller secondary)
> Has anyone built (or raytraced) one of these?
This kind of rhetorics does not serve any purpose. If you DID your homework and math, and proven that such a system can work (or even better, made a workable prototype), maybe you could publish it in Applied optics or maybe ATMJ. But nobody is going to sit and do raytracing for you on the basis of pure contemplation.
Sorry, but that's just how it is.
Bratislav
PS I suggest you try to MAKE some of convex torical hyperboloids for tilted Ritchey-Chretien; then you'll know why