I've used a lot of exec bifocals and trifocals over the years and am
curious about one thing.

Why is it that the seg lines are not as perfect as they used to be?

I mean I remember them calling exec glass bifocals "no jump" because
there was no image displacement at the line, as there was with all other
types that obviously must have prism (base up for flat tops, down for
round ) at the line. But the execs (e-line or Franklins) always had a
crisp, prism free junction at the thinnest point on the "ledge" and that
point was where the two front curves (or 3 in trif) coincided
tangentially. It was always a mystery to me how these surfaces were
generated at the factory.

Now it's even more a mystery.  Plastic execs now almost always have
prism in the seg at the line.  I just checked out a pair that has 1 P.D.
of base down O.U. at the seg, and while the ledge has a minimal ledge
standoff point, it is not zero like the good old days. Sometimes this
prism is so bad I reject the lenses as defective, and sometimes the
optics are even smeared very close to the line, as if the ledge has been
"rolled".

So what gives?  Is the technology lost?  Is there some reason for this
mess?  I still like execs and use them at least 1 or 2x per month.

w.stacy, o.d.  (I think I'll cc this to whoever makes the blanks.  Any
ideas on who makes them?)