3B Scientific Laser Optics Supplemental Set - Manual (Page 29)

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E22b Model of short-sighted eye
(U17300, transparency A)
Display rays parallel to the optical axis intersect after
passing through uncorrected eye lens at one point of
the optical axis before the retina.
Place the eye lens (2) directly behind the line O
2
and
the correction lens (5) between the lines O
1
and O
2
.
E22c Model of long-sighted eye
(U17300, transparency A)
Display rays parallel to the optical axis intersect after
passing through uncorrected eye lens at one point of
the optical axis after the retina. A correction lens must
be convergent. The focal length f' of the system of eye
lens and the correction lens is:
f
f f
f f
’
’ ’
’ ’
=
+
1 2
1 2
where f
1
' is the focal length of the eye lens and f
2
' is
the focal length of the correction lens.
E23a Correction of spherical aberration by
reducing the beam diameter
(U17300/U17301)
Spherical aberration of a lens can be reduced by re-
ducing the diameter of the beam which impinges the
lens. The rays which are far away from the optical axis
must be obscured.
E23b Correction of spherical aberration by
combination of lenses
(U17300, transparency E)
The spherical aberrations of divergent and convergent
lenses have an inverse effect. By a convenient
combination of these two types of lenses the aberra-
tion can be corrected. The aberration
∆
f = f
1
– f
2
is
defined as the difference between the focal length f
1
of marginal beam rays and the focal length f
2
of
paraxial rays. In the case of a convergent lens the
aberration is of a plus sign and for a divergent lens it is
a minus sign.
Retina
Eye lens
Eye lens
Retina
Correction lens (5)
Correction lens (4),
(between O
1
and O
2
)