> db.tf.find( { "transforms.header.stamp": { $lt: new Date(1396512603500), $gte: new Date(1396512602000) } } ).explain()
{
    "cursor" : "BtreeCursor transforms.header.stamp_1",
    "isMultiKey" : false,
    "n" : 49,
    "nscannedObjects" : 49,
    "nscanned" : 49,
    ....
    "millis" : 3,
    "indexBounds" : {
        "transforms.header.stamp" : [
            [
                ISODate("2014-04-03T08:10:02Z"),
                ISODate("2014-04-03T08:10:03.500Z")
            ]
        ]
    }
    ....
}

> db.tf.find( { "transforms.header.stamp": { $lt: new Date(1396512603500), $gte: new Date(1396512602000) } } ).explain()
{
    "cursor" : "BtreeCursor transforms.header.stamp_1",
    "isMultiKey" : true,
    "n" : 49,
    "nscannedObjects" : 20489,
    "nscanned" : 20489,
    ....
    "millis" : 645,
    "indexBounds" : {
        "transforms.header.stamp" : [
             [
                 true,
                 ISODate("2014-04-03T08:10:03.500Z")
             ]
        ]
    }
    ....
}

> db.tf.find( { "transforms.header.stamp": { $type: 4 } } ).count()
0

> db.tf.find( { "transforms.header.stamp": { $type: 9 } } ).count()
554672

> db.tf.find( { "transforms.header.stamp": { $type: 17 } } ).count()
Mon Dec 22 11:53:19 uncaught exception: count failed: {
    "code" : 13111,
    "ok" : 0,
    "errmsg" : "13111 wrong type for field () 17 != 9"
}