Index: trunk/ppSim/src/ppSimMakeSky.c
===================================================================
--- trunk/ppSim/src/ppSimMakeSky.c	(revision 18993)
+++ trunk/ppSim/src/ppSimMakeSky.c	(revision 20366)
@@ -82,6 +82,5 @@
 	      // add a scattered light term to the flat-field images
 	      if (type == PPSIM_TYPE_FLAT) {
-		float xF = 2.0*(xFPA / dXfpa) - 1.0;
-		scatterRate = scatterFrac * PS_SQR(xF);
+		  scatterRate = scatterFrac * PS_SQR(xFPA);
 	      }
 
@@ -94,5 +93,6 @@
 	    // used later to modify the star and galaxy photometry 
 	    if (expCorr) {
-	      expCorr->data.F32[y][x] = realExpTime / expTime;
+		// exposure correction is (effective exposure time) * (flatValue)
+	      expCorr->data.F32[y][x] = flatValue * realExpTime / expTime;
 	    }