Page 64 - PowerPoint 演示文稿

6

Lens Aberrations

One of the first decisions to be made while dispensing a new prescription
is the choice of lens form. When the eye views along the optical axis of the
spectacle lens, the form of the lens does not matter and image formed by
the lens is not afflicted with any defects or aberrations which might affect
its sharpness or its shape. But in actual world, the eyes turn behind the lens
to view through off-axis visual points and it is then that the form assumes
importance.

Figs 6.1A to C: Our eyes turn behind the lens to view through the off-axis. It is then
the lens aberrations assume importance (A) Primary direction, (B) Secondary
direction, (C) Tertiary direction