COMMENTS ON THE GRAVITATIONAL LENSING MAGNIFICATION

We rederive a relation between gravitational lensing magnification rel ative to the standard Friedmann distance and one relative to the Dyer- Roeder distance by investigating the null geodesic deviation equation. We show that the relation comes from a natural consequence of the def inition of the lensing magnification matrices and is not based on the averaging of the magnifications, which has conventionally been used to derive it. We therefore conclude that the relation is true for each i ndividual ray bundle.