Index: trunk/psModules/src/objects/pmSourceIO_CMF_PS1_V1.c
===================================================================
--- trunk/psModules/src/objects/pmSourceIO_CMF_PS1_V1.c	(revision 26916)
+++ trunk/psModules/src/objects/pmSourceIO_CMF_PS1_V1.c	(revision 26964)
@@ -69,9 +69,12 @@
     float magOffset = NAN;
     float exptime   = psMetadataLookupF32 (&status1, fpa->concepts, "FPA.EXPOSURE");
-    float zeropt    = psMetadataLookupF32 (&status2, imageHeader, "ZPT_OBS");
-    float zeroptErr = psMetadataLookupF32 (&status2, imageHeader, "ZPT_ERR");
+    float zeropt    = psMetadataLookupF32(&status2, fpa->concepts, "FPA.ZP");
+    if (!isfinite(zeropt)) {
+        zeropt    = psMetadataLookupF32 (&status2, imageHeader, "ZPT_OBS");
+    }
     if (status1 && status2 && (exptime > 0.0)) {
         magOffset = zeropt + 2.5*log10(exptime);
     }
+    float zeroptErr = psMetadataLookupF32 (&status2, imageHeader, "ZPT_ERR");
 
     // if the sequence is defined, write these in seq order; otherwise
@@ -477,5 +480,5 @@
         }
 
-# endif	
+# endif
         psArrayAdd (table, 100, row);
         psFree (row);
Index: trunk/psModules/src/objects/pmSourceIO_CMF_PS1_V2.c
===================================================================
--- trunk/psModules/src/objects/pmSourceIO_CMF_PS1_V2.c	(revision 26916)
+++ trunk/psModules/src/objects/pmSourceIO_CMF_PS1_V2.c	(revision 26964)
@@ -69,9 +69,12 @@
     float magOffset = NAN;
     float exptime   = psMetadataLookupF32 (&status1, fpa->concepts, "FPA.EXPOSURE");
-    float zeropt    = psMetadataLookupF32 (&status2, imageHeader, "ZPT_OBS");
-    float zeroptErr = psMetadataLookupF32 (&status2, imageHeader, "ZPT_ERR");
+    float zeropt    = psMetadataLookupF32(&status2, fpa->concepts, "FPA.ZP");
+    if (!isfinite(zeropt)) {
+        zeropt    = psMetadataLookupF32 (&status2, imageHeader, "ZPT_OBS");
+    }
     if (status1 && status2 && (exptime > 0.0)) {
         magOffset = zeropt + 2.5*log10(exptime);
     }
+    float zeroptErr = psMetadataLookupF32 (&status2, imageHeader, "ZPT_ERR");
 
     // if the sequence is defined, write these in seq order; otherwise