The Microchannel X-ray Telescope (MXT) is one of four instruments on the Space-based multi-band Variable Objects Monitor satellite mission, launched on the 2024 June 22nd. The MXT is a narrow-field-optimized, lobster eye X-ray focusing telescope, consisting of an array of 25 square MPOs, with a focal length of 1.14 m and working in the energy band 0.2–10 keV. The design of the MXT optic (MOP) is optimized to give a 1° FoV to match the detector size, but the optic has the unique characteristics of a lobster eye design, with a wide FoV of 6° diameter, and a PSF, which is constant over the entire FoV. The MPOs on the Flight Module MOP have a pore size of 40 μm giving the optimum thicknesses across the aperture of 2.4 mm in the center and 1.2 mm at the edges. Using specific target sources, the in-orbit calibration of the optic is described here, and compared to the extensive on-ground calibration, which was carried out at the PANTER test facility, MPE, Germany. The design and limitations of the electron diverter, situated directly behind the optic, are also discussed.