If the sealing location is heat sensitive and requires minimum heating, a laser can be used to concentrate the heating on the patterned sealing region. Most optical instruments can be designed to be close to diffraction-limited performance if tested in a controlled environment. Sources of many errors occur during actual operating conditions. It is difficult to control residual aberrations caused by misalignment, thermal changes, and atmospheric turbulence limitation. The use of multiple mirrors and segmented primary mirrors arc technique, with proper phase alignment, can achieve maximum optical instrument resolution.
Active control is required to maintain alignment between mirrors or mirror segments.
Errors to concern the optomechanical engineer are optical component decentering optical component misalignment mirror segment misalignment mirror figure. This information can be processed as feedback to the active control system. An actively controlled primary mirror or an auxiliary deformable mirror can be for wavefront compensation. The primary mirror, either segmented or a flexible face plate, can be refigured by numbers of actuators driven by a data processor. Feedback corrections to an actuator-driven secondary mirror can compensate for misalignments, decentering, and defocusing.