In the textbook Astrophotography for the Amateur, author Michael Covington states that Newtonians (Reflectors) normally only have 1-2cm of back focus, which would be insufficient for 35mm film (or full-frame digital) astrophotography. The work-around that the author suggests for this problem is modifying the telescope to bring the primary mirror forwards about 5cm. From what I've read online, it seems this involves either substituting the screws holding the mirror for longer ones, and/or cutting the tube itself.
I'm interested in Reflectors because of their relatively fast focal ratios and modest pricing. They also seem to be one of the more often recommended types of telescopes for imaging, which makes it all the more surprising to me that they are generally unusable for prime astrophotography until they have been modified. My copy of this book is the revised edition published in 1991. Has anything changed in the design of reflectors so that they are better suited to full-frame imaging without modification? Are there any Reflectors available that are preconfigured for full-frame prime focus astrophotography?