Optical Principle - Weco cad III Operation Manual

3.4 Optical principle

The user is looking through a partly
transparent mirror 2 on a LCD that is
illuminated from the back and tha shows
the decentration values and graphics.
The lens is displayed in actual shape (not
reversed) via mirror 1 and 2. The
decentration point for blocking needs to
be in the following position: distance b
from mirror 2 (measured by mirror 1)
which equals the distance a from mirror 2
to the display. To achieve this one has to
lower or lift the lens. This procedure will
happen automatically when the
<BLOCK> key is pressed.
10
Abb. 4
This imaging of the lens on the display
avoids image shifts or systematical
blocking errors since the distance
between the image and the display
equals zero.
This means that the system is parallax
free i.e. the relation of a point on the lens
with that of a point on the display remains
unchanged regardless the position of the
observer.This is particulary inportant with
prismatic corrections since it is the only
way to transfer the correct refraction
values to the final eye glasses.