The meaning of PARFOCAL is being or having lenses or lens sets (such as eyepieces) with the corresponding focal points all in the same plane.
order of 20/12 or even 20/10. The process is not yet done, however, in the Symfony. The diffractive optics are then used to expand the range of vision. Expanding the depth of focus degrades the tack-sharp “starting point” (something must be lost, as Dr. Chang pointed out), but ...