Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE photos (id VARCHAR, camera_lens_id VARCHAR); CREATE TABLE camera_lens (id VARCHAR, camera_lens_id VARCHAR)
### Question:
How many camera lenses are not used in taking any photos?
### Answer:
SELECT COUNT(*) FROM camera_lens WHERE NOT id IN (SELECT camera_lens_id FROM photos)