Returns the minimal distance from an object at which the gravitational lensing effect becomes visible and eventually usable for magnification.
The mass of the object in kg
The radius of the object in meters
The computed distance in meters
https://astronomy.stackexchange.com/questions/33498/what-is-the-gravitational-lensing-focal-distance-of-a-white-dwarf-star
Returns the minimal distance from an object at which the gravitational lensing effect becomes visible and eventually usable for magnification.