Pete...took me a short while. Mag 24.1 is possible. There is also a Canadian conspiracy happening here
as names like Ceravolo and Boltwood came up in the May 1999 issue of S&T.
Paul Boltwood (yes, the cloud sensor guy) *made* a camera fitted with a front illuminated CCD and won the "deep-field challenge" back then.
Paul gave an excellent write up, and the results suggest with a modern back illuminated camera and dark skies Mag 26 may be possible.
Einstein rings! Pah! I laugh at you!