The UVOT is a modified Ritchey-Chrétien telescope with a 30 cm aperture and an f-number of f/12.72. It operates in the wavelength range of 1600-6000 Å, although there is some low-level response in between 6000 Å and 8000 Å. It is mounted on the optical bench with the BAT and the XRT as shown in Figure 8 and co-aligned with the XRT. An 11-position filter wheel houses the UV and optical grisms, a 4-times magnifier, broadband UV and optical filters, a clear ``white-light'' filter, and blocking filter. Photons register on a micro-channel plate intensified charged-coupled device. These can operate in a photon counting mode and are capable of detecting very low light levels. When flown above the atmosphere the UVOT possesses the equivalent sensitivity of a 4 m ground-based telescope, capable of detecting a 22nd magnitude B star in 1000 seconds using the white-light filter. An outline of the UVOT's characteristics can be found in Table 7.