Changing the focus of the telescope moves the secondary mirror perpendicularly away from or toward the primary mirror. The secondary mirror is limited in how far it can move. If you command the telescope to change its focus to a value it cannot achieve, it will continue to send the signal, however, no more motion will occur once it reaches its physical limit. The software will continue to send the signal until it reaches the desired focus, but since the focus position will never be achieved the signal will be sent indefinitely.

Symptoms:

1. Trying to set a new focus position in DFMTCS does not do anything when “Apply” is clicked
2. The Left-hand status boxes report “SETTING” in red letters

Solution:

1. Press the “Cancel” button on the Control Computer's front panel. This tells the CC to stop sending the command.
   1. The status boxes that reported “SETTING” should now be empty
2. Change the focus value so that it shifts in the opposite direction that you attempted
   1. If you were trying to lower the focus value when it stopped moving, then increase the focus value.
   2. If you were trying to raise the focus value when it stopped moving, then decrease the focus value.