Excellent question, and here on earth, nothing I can think of. But what if we shift the parameters and exclude the gravitational effect? People with cataracts experience halos which is similar to lensing. Photographs of moving vehicles show tail light "trails" which might be considered a type of lensing. Not getting into the math here, just speculating about what might be potential answers for your question.
At one time it was postulated that huge numbers of tiny black holes might answer questions of dark matter. But, then one would have to figure out how those black holes came about.
