Depth from stereo camera with different focal lengths

I am working on estimating the depth of a stereo camera. However, for a specific purpose, I need to use two cameras with different FOV and focal lengths.
After a lot of Google research, I know that I can still calibrate the two cameras and fix them to create a disparity map, but I don't know how to convert the disparity map to depth because their focal length is different, satisfy the model at
http: // docs .opencv.org / trunk / dd / d53 / tutorial_py_depthmap.html

Does anyone have a solution?

Thank!