In article , Steve Willner
writes:

In article ,
"Richard D. Saam" writes:
In as much as lensable mass varies with universe density ~H^2/G (1+z)^3
then "high-z lenses will to be more powerful than low-z lenses"

I don't understand this. Lensing depends on the contrast between
high and low density regions, and all standard models have that
contrast _increasing_ with time (i.e., larger at low redshift).

Yes, objects tend to grow more massive with time. But for a constant
mass, there is an optimal redshift. So, the "power" will be a
combination of these two things.