Meniscus lenses have one surface concave and
one convex. With suitable radii of curvature they can have an
overall positive effect that is they will form a real image of
a distant object.
Meniscus lenses can be very useful when used in conjunction with
an achromatic doublet to create a lens pair with a shorter focal
length than one lens can achieve.
Positive meniscus lenses are designed to minimize spherical aberration.
They have one convex and one concave surface. When used in combination
with another lens, a positive meniscus lens will shorten the focal
length and increase the NA of the system.
Negative meniscus lens is used to increase the focal length of
another lens while maintaining the angular resolution of the optical
assembly. This lens shape is best used when one conjugate is relatively
far from the lens.
Like the positive meniscus lenses they can be used in conjunction
with an achromatic doublet to increase the focal length.
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