what is the name of the camera lens in the mountains id 2?
SELECT T2.name FROM photos AS T1 JOIN camera_lens AS T2 ON T1.camera_lens_id   =   T2.id WHERE T1.mountain_id  =  2
name of the camera lens used in photos of mountains with id 2 refers to joining tables photos and camera_lens on camera_lens_id and selecting the name of the lens where mountain_id = 2;