Common imaging train

Celestron EdgeHD 11 + 0.7× reducer + ASI2600MC Pro

The 0.7× reducer for the EdgeHD 11 keeps the native back focus, measured from the reducer's rear surface; its 42 mm image circle is just under full frame. On an EdgeHD the T-adapter is part of the optical length: Celestron's own figure for it is counted here, and the camera threads onto its T2 end. The T2 bore is the limit — fine for APS-C, not for full frame. The large T-adapter and the two boxed ZWO extenders meet the figure within Celestron's half-millimetre.