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Observing Constraints

To reach the desired instrument performance GPI is constrained both in the suitable weather conditions and the elevation of the target being observed. 

The nominal weather conditions for which the performance data has been specified is IQ70 CC50, please look at ContrastLimiting magnitudes for instrument and internal wavefront sensorsOptical throughput and Polarimetry for more details on how the performance is affected by observing at other conditions i.e. IQ85 and CC70. 

For the AOWFS and the LOWFS to work then the elevation is limited to Zenith distances ≤40°, with a possibility to reach Zenith distances of 50° with a lower performance. The wavefront sensors are designed to reach peak performance on point sources and the performance decreases by observing extended objects, more details can be found at Extended Objects