The 'focus' property of PerspectiveCamera does not work

i know PerspectiveCamera have a Propertie called ‘.focus’ that able to achieve depth-of-field effects.i set it and updateProjectionMatrix () but the result is not change

As stated in the docs: This parameter does not influence the projection matrix unless a StereoCamera is being used.

how to do if i want to achieve DOF effects?thx

You need post-processing for this. Check out the official examples:

thank you for help,i will have a try