TEST 1:
mental ray:
eye rays: 397901
shadow rays: 343112
rendering time: 3.44s
rays per sec: 215410.75
shadow rays per eye ray: 0.86
elvish ray:
eye rays: 500673
shadow rays: 437933
rendering time: 4.36s
rays per sec: 215276.61
shadow rays per eye ray: 0.87
TEST 2:
mental ray:
eye rays: 397901
shadow rays: 343112
rendering time: 3.44s
rays per sec: 215410.75
shadow rays per eye ray: 0.86
elvish ray:
eye rays: 458146
shadow rays: 404233
rendering time: 2.77s
rays per sec: 311328.15
shadow rays per eye ray: 0.88
why mental ray can save many rays when the sampling options are the same?...