Allow read aperture while moving.

src/iris_diaphragm.py

@@ -149,7 +149,7 @@ class IrisDiaphragm (PyTango.Device_4Impl):
         self.write_position(new_aperture)
 
     def is_Aperture_allowed(self, req_type):
-        return self.get_state() in (PyTango.DevState.ON,)
+        return req_type is PyTango.AttReqType.READ_REQ or self.get_state() in (PyTango.DevState.ON,)
 
     def read_StepSize(self, attr):
         # self.debug_stream("In read_StepSize()")