Update ZMQ Message Reference

ZMQ-Message-Reference.md

@@ -365,6 +365,19 @@ msg2 = ['modified zonePlate definition',
 
 ## 'zonePlateFocus'
 
+Set the focus position. Data is a dictionary with the following fields:
+* "target": "Sample"|"OSA" : The object being focused on.
+* "action": "calibrate"|"calculate" : Indicate whether to adjust the focus position, or simply return the calculated position (for setting up a focus scan).
+* "cursorPosition": Position value (in microns) on the zonePlateZ stage where the focus should be set.
+* "setDOsa": (Optional) Boolean integer to indicate that the OSA gap should be set (1/True) for the focus adjustment.
+
+Note that focusing on the OSA means that the zonePlateZ stage offset would be adjusted to calibrate the distance between the zone plate and the OSA.
+
+Example:
+```
+['zonePlateFocus', {'target': 'Sample', 'action': 'calibrate', 'cursorPosition': -1573.4942215445321}]
+```
+
 ## 'oscilloscopeDefinition'
 
 Parameters describing the function of the oscilloscope view of periodic detector readings. Data is a dictionary with the following fields:
@@ -382,7 +395,7 @@ Example:
 
 ## 'focusType'
 
-Set the autofocus mode of the zoneplate. Data must be one of the following strings:
+Turn on/off the autofocus feature of the zoneplate Z stage. Data must be one of the following strings:
 * "Auto": zoneplate will move to keep focal plane in the calculated position whenever the energy is changed.
 * "Static": zoneplate stage will not respond to changes in energy.