Petzval field curvature

Petzval field curvature, named for Joseph Petzval,[1] describes the optical aberration in which a flat object normal to the optical axis (or a non-flat object past the hyperfocal distance) cannot be brought properly into focus on a flat image plane.

Most current photographic lenses are designed to minimize field curvature, and so effectively have a focal length that increases with ray angle.

[citation needed] Large mosaics of sensors (necessary anyway due to limited chip sizes) can be shaped to simulate a bend over larger scales.

The primary way to control this aberration is by inserting further optical elements which counteract the curved focal plane off axis.

Using a small aperture to limit the effect of field curvature greatly decreases the light collecting power of the lens.