Database
[{_id:ObjectId("54060b811e8e813c55000058")},{_id:ObjectId("54060e9e1e8e813c55000059")},{_id:ObjectId("540738e082fa085e5f000015")},{_id:null}]
Query
db.collection.find({$expr:{$gte:[{$indexOfCP:[{$toString:"$_id"},{$toLower:"00005"}]},0]}})