In optical microscopy, field curvature is an optical aberration that most of the experienced microscopists are familiar with. Field curvature occurs when lenses that have curved surfaces are used.
Field curvature originates when visible light rays are focused through a lens that is curved. The image plane that is produced by the curved lens will be curved. This curved surface can be referred to as a curved Petzval surface. The curvature of the Petzval surface is the reciprocal of the radius of the lens, and this is referred to as the Petzval field curvature.
Field curvature causes the specimen when observed through the eyepiece of the microscope to either appear focused in the center or on the edges. However, not both the center and the edge will be brought into focus.
For microscopists, field curvature aberration is not a serious problem. It is simply a matter of utilizing fine focus to adjust small deficiencies in the focus of the specimen. Unfortunately, field curvature is a major problem for photomicrography when sections of the photomicrograph are not properly focused.
It is very rare that field curvature is eliminated.