A:Answer For the CPC 1100 GPS SCT, you will need the Celestron SCT T-Adapter #93633-A and a Celestron Nikon T-Ring #93402. Keep in mind that the clear aperture of the 93633-A is 38mm, and the sensor diagonal of the full-frame D810 is 43.6mm, so the extreme corners will vignette. Celestron only makes M48 T-adapters for the EdgeHD 9.25”, 11”, and 14” telescopes.