The Sloan Digital Sky Survey (SDSS) covers 8,000 square degrees of northern sky to fainter than 14th magnitude; a catalog compiled with the Carlsberg Meridian Telescope
covers the sky between declinations -30[degrees] and +50[degrees] in the Sloan-r' band; and the All-Sky Automated Survey lists stars from 8th to 14th magnitude, but only for the V band.
We obtained the tube inserts from Meridian Telescopes
, Mt Clemens, Michigan, USA.
Eventually he came upon an inexpensive helical focuser by Meridian Telescopes