Method for assembling lens module with image sensor

A method for assembling a lens module with an image sensor, the lens module comprising a lens barrel and at least one lens received in the lens barrel, the method comprising:

• providing a holder comprising a first receiving space for receiving the lens barrel and a second receiving space for receiving the image sensor;
• disposing the image sensor in the second receiving space;
• locating the lens barrel at a first position in the first receiving space;
• providing a clamp having a light source for generating a light beam;
• casting the light beam on the lens module to allow the lens module to converge the light beam into a light spot on the image sensor;
• determining if the light spot is at its smallest to determine if a distance between the lens module at the first position and the image sensor is equal to a focal length of the lens module;
• moving the lens module to a second position in the first receiving space of the holder to achieve a predetermined distance from the first position;
• and
• positioning the lens module at the second position.