
9.1.
Field Lenses, Flatteners 207
9.1.
FIELD LENSES, FLATTENERS
A field lens is an element that is placed at or near an image plane in an optical
system. One application for such a lens, as noted in Section 5.7, is that of
flattening a curved image surface. Before discussing this application, and others,
we consider the aberrations introduced when an object or image lies close to an
optical surface.
9.1.a.
ABERRATIONS
The aberration coefficients for a general surface are given in Table 5.5. For an
object close to the surface, take F
fi*om
Table 5.5, replace / using Eq. (2.2.4), and
let s <^R. The result obtained is
s
\n'2
J
(9.1.1)
Given th ...