Does anyone know what is the difference between transparency and overprint?
In other words: if I print 100% cyan and then 100% magenta with 50% opacity, how is it different from printing 100% cyan and then 50% magenta with overprint?
Using opacity will still knockout what is below the object. Overprint, obviously, wont.
Overprint has a tendency to look like "multiply" blend mode. In fact, in many cases you can use the Multiply blend mode rather than overprinting.
Opacity tends to look much more like a mixed ink.
Left: 100%M set to 50% opacity. Center: 50%M set to overprint. Right: 50%M set to multiply blend mode.