diff --git a/asibfm700/asibfm700_configfile.h b/asibfm700/asibfm700_configfile.h
index 9fec087..4988db7 100644
--- a/asibfm700/asibfm700_configfile.h
+++ b/asibfm700/asibfm700_configfile.h
@@ -773,7 +773,7 @@ siteElevation = 2070.0
 #    celestial coordinate transformation
 
 # wavelength at which refraction is calculated (in mkm)
-refractWavelength = 0.55
+refractWavelength = 0.5
 
 # an empty filename means default precompiled string
 leapSecondFilename =