Correlation of IR and Opticical Variability in NGC4151
  We combine all published NIR and optical photometrical observations of NGC 4151 as well as our new unpublished yet data which can be used for determination of time delays between optical and NIR variations. Before we have found change of time delay value for variations in K and L filters for different states of the luminosity. Here we are considering new data for deep minimum after the very high state of the nucleus. We conclude that dust recovering time after the high state is for any case more then several years. 
V. L. Oknyanskij, V.M. Lyuty, O.G. Taranova, V.I. Shenavrin