ENR CTIO Blanco 4-m 2021-06-26

The telescope opened about an hour late due to humidity.

The telescope was unable to maintain focus for more than ~20 minutes, so the focus needed to be adjusted frequently.

The problems with the focus increased during the second half of the night. During the acquisition process for some targets, the focus value in the TCS window would spontaneously change by hundreds of units. Sometimes the focus would return to the original value on its own and other times it would settle on a value very different from the original value. Everntually, the focus in the TCS changed to invalid value (-8909). The operator was unable to regain control of the focus, so we had to end observations for the night.