Seven Seidel coefficients (effectively wavefront aberration terms)
SA3- spherical aberration (S1)
COM3 - coma (S2)
AST3 - astigmatism (S3)
PETZ3 - Petzval (field curvature) (S4)
DIST3 - distortion (S5)
LCOLOR - lateral color (C1)
TCOLOR - longitudinal color (C2)
For lenses at higher numerical apertures and field sizes, third-order aberrations are insufficient for describing all of the aberrations. High order aberrations are induced because a surface is operating in an aberrated beam. Fifth-order and even the seventh-order coefficients need to include in the design.
Fifth-order aberrations
SA5 - spherical aberration
COM5 - coma
AST5 - astigmatism
PETZ5 - Petzval
DIST5 - distortion
TOBSA - tangential oblique spherical aberration
SOBSA - sagittal oblique spherical aberration
LCOMA - Elliptical coma
Singlets
plano-convex, plano-concave, equi-convex, or equi-concave. Most are made of BK7 lenses may have large aberrations. They are mostly used when apertures are quite small or when aberrations are not important.
Field flatteners
Although plano-concave singlets for field flattener do not correct astigmatism, the improvement in field curvature is significant.
Doublet and flattener
Meniscus singlets
The earliest anastigmats flattened the field by using a think meniscus, which separated the positive and negative outer surfaces. Approximating an aplanatic condition on the front surface and a rear surface that is almost concentric with the marginal ray when used in the converging beam after a doublet. The combination has significant better resolution than the equivalent doublet. However, meniscus lens is not color corrected. At the time there were no antireflection coatings, designers tried to minimize the number of air-glass surfaces. For this reason, most of the early anastigmats were limited to two cemented meniscus components.
Doublet and meniscus
Doublets and triplets
Spherical aberration, coma, and chromatic aberration are corrected.
Cemented triplets
Symmetrical triplets have zero coma, distortion, and lateral color at unit magnification. When it is used at infinity conjugates, the aberrations may be small enough for some applications.
Single lens for disposable camera
They use a single plastic lens, which can be aspheric, and a film (ASA 400-800) that is curved around a cylindrical surface. Although it is possible to correct coma, the astigmatism is then quite large. Moreover, field curvature, axial and lateral color are not corrected, but at an aperture of f/16 the performance is just acceptable.
