--- a/bin/match-n-shift
+++ b/bin/match-n-shift
@@ -257,7 +257,9 @@
   -n | --noransac       No ransac detection, useful for fisheye images
   -r | --refine         Refine the found control points using the
                           original images, delete unrefinable.
-  -f | --projection     Panotools style input projection number
+  -f | --projection     Panotools style input projection number. Use
+                          0 for rectilinear, 2 for circular fisheye and
+                          3 for full-frame fisheye images.
   -v | --fov            Horizontal field of view in degrees
   -k | --selection      Crop selection boundary, eg -459,2459,-57,2861
   -c | --clean          Delete all temporary files afterwards.