Ratios: A
comparison of a constant (fill) to a variable
(main) expressed as a fraction.
1st # = fill; 2nd # = main light
1:1 = flat
light, no shadows
1:2 = 1 stop
diff. (shadow/highlight)
1:4 = 2 stop
diff. (shadow/highlight)
1:8 = 3 stop
difference
1:8+ = no detail in the shadow area