Does a gravitational lens have a focal point like an optical lens?

[scupydog]

Does a gravitational lense have a focal point, like a nomal lense but as a focal point sphere/horizon. if so is there a formula that relates the mass of the GL with the radius of its focal horizon. Happy xmas.

 

[Kracatoan]

I would imagine it does, but no-one has bothered to make a formula to describe it seeing as gravitational lensing isn't caused by a nice uniform lense, but by an uneven body of mass, so it would be very difficult to describe the exact effect in a formula.

 

[scupydog]

Thx for reply, i think i have found what i was looking for