diff --git a/esbo_etc/classes/psf/IPSF.py b/esbo_etc/classes/psf/IPSF.py
index 0b4f690..748bfa4 100644
--- a/esbo_etc/classes/psf/IPSF.py
+++ b/esbo_etc/classes/psf/IPSF.py
@@ -10,7 +10,7 @@ class IPSF(ABC):
     """
     @abstractmethod
     def calcReducedObservationAngle(self, contained_energy: Union[str, int, float, u.Quantity],
-                                    jitter_sigma: u.Quantity = None) -> u.Quantity:
+                                    jitter_sigma: u.Quantity = None, obstruction: float = 0.0) -> u.Quantity:
         """
         Calculate the reduced observation angle in lambda / d_ap for the given contained energy.
 
@@ -20,6 +20,8 @@ class IPSF(ABC):
             The percentage of energy to be contained within a circle with the diameter reduced observation angle.
         jitter_sigma : Quantity
             Sigma of the telescope's jitter in arcsec
+        obstruction : float
+            The central obstruction as ratio A_ob / A_ap
 
         Returns
         -------
diff --git a/esbo_etc/classes/psf/Zemax.py b/esbo_etc/classes/psf/Zemax.py
index 61390e1..58c0bec 100644
--- a/esbo_etc/classes/psf/Zemax.py
+++ b/esbo_etc/classes/psf/Zemax.py
@@ -67,7 +67,7 @@ class Zemax(IPSF):
 
     # @u.quantity_input(jitter_sigma=u.arcsec)
     def calcReducedObservationAngle(self, contained_energy: Union[str, int, float, u.Quantity],
-                                    jitter_sigma: u.Quantity = None) -> u.Quantity:
+                                    jitter_sigma: u.Quantity = None, obstruction: float = 0.0) -> u.Quantity:
         """
         Calculate the reduced observation angle in lambda / d_ap for the given contained energy.
 
@@ -77,6 +77,8 @@ class Zemax(IPSF):
             The percentage of energy to be contained within a circle with the diameter reduced observation angle.
         jitter_sigma : Quantity
             Sigma of the telescope's jitter in arcsec
+        obstruction : float
+            The central obstruction as ratio A_ob / A_ap
 
         Returns
         -------