diff --git a/focus_utils.py b/focus_utils.py
index 3228bb9..e289fac 100644
--- a/focus_utils.py
+++ b/focus_utils.py
@@ -580,7 +580,7 @@ def getFocusCalcCmdlinePars(parser):
     parser.add_argument(
         "-o",
         "--data-curve",
-        help="filename of focussing curve data file",
+        help="filename of focussing curve ASCII data file",
         type=str,
         default=None,
     )
@@ -613,7 +613,8 @@ def getFocussingSequenceCmdlinePars(parser):
 
     parser.add_argument(
         "--foc-file",
-        help="Rootname of output focussing images. Default is 'focus.fits'.",
+        help="Rootname of output focussing images. Default is 'focus.fits'. The algorithm generates files of sequence as "
+        "'rootname_0001.rootname_ext, rootname_0002.rootname_ext ... rootname_NNNN.rootname_ext', where NNNN is an index number of acquisition.",
         type=str,
         default="focus.fits",
     )