  The Extreme Universe Space Observatory on a Super Pressure Balloon 2
(EUSO-SPB2), successfully launched from Wanaka, New Zealand on May 13, 2022, is
a precursor for a space-based astroparticle observatory such as the Probe Of
Extreme Multi-Messenger Astrophysics (POEMMA). EUSO-SPB2 flew two custom
telescopes. Both have UV/UV-visible sensitivity and feature Schmidt optics. The
Fluorescence Telescope (FT) measures ultra-high energy cosmic rays by looking
down. The \v{C}erenkov Telescope (CT) searches for neutrino signatures by
looking toward Earth's limb. The two telescopes each have a 1 m diameter
entrance pupil and segmented glass mirrors that collect light from extensive
air showers at the PeV and EeV-scale. Here we describe the FT telescope optics
together with the results of the FT field tests at the Utah Telescope Array
(TA) site from August/September 2022. The FT recorded the night sky background,
lasers, and artificial point sources. The field tests included an absolute
photometric calibration of the FT telescope that is compared to a piece-wise
laboratory calibration.
