If an encrypted field has both an equality index and a range index, the equality index will be used as before to answer equality queries. If an encrypted field only has a range index, however, query analysis should rewrite the query to correctly return results without an equality index.

{x: {$eq: 26}}
will be rewritten to
{$and: [{x: {$gte: 26}}, {x: {$lte: 26}}]}