in the Doppler beaming factor between the two types of blazars. We finally encourage a systematic NIR multiwavelength study of a large, well defined sample of BL Lac objects and their immediate environments with the new generation large NIR arrays.

Acknowledgments {#acknowledgments .unnumbered}
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JKK acknowledges a research grant from the Academy of Finland during the initial part of this work. We thank the anonymous referee for prompt comments. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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