Uploaded October 2025 | Updated September 2026, 2 hours ago
Field curvature is a form of optical aberration that affects the shape of an optical system’s focal plane. For an on-axis collimated beam, the focal plane is located along the optical axis at a distance equal to the system’s back focal length, also referred to as its working distance.
Field curvature only presents with off-axis rays, since on-axis rays converge along the optical axis. The shape of the focal plane can be observed by tracking a collimated beam’s point of focus across a range of off-axis angles. For small off-axis angles, the amount of field curvature may be negligible. But for larger angles, greater deviation from the on-axis focal plane has detrimental effects for imaging and laser scanning applications.
In imaging applications, most camera imaging sensors are flat. When optical systems have a flat focal plane, they can produce images that are in-focus across the whole sensor. But when field curvature is present, the plane of focus can only be shifted between the edges of the image and its center.
Single element systems often suffer from field curvature. A field-flattening element like a plano-concave lens can reduce its severity, but in aberrated systems it can create a tradeoff. In this case, worsening distortion.
Field-flatteners best minimize field curvature when other forms of optical aberrations aren’t present. Singlet systems with lots of aberration can be replaced with additional elements to reduce aberration while maintaining a similar effective focal length. With additional aberrations reduced, the addition of a field-flattener effectively eliminates field curvature.
Field curvature is a form of optical aberration that affects the shape of an optical system’s focal plane. For an on-axis collimated beam, the focal plane is located along the optical axis at a distance equal to the system’s back focal length, also referred to as its working distance.
Field curvature only presents with off-axis rays, since on-axis rays converge along the optical axis. The shape of the focal plane can be observed by tracking a collimated beam’s point of focus across a range of off-axis angles. For small off-axis angles, the amount of field curvature may be negligible. But for larger angles, greater deviation from the on-axis focal plane has detrimental effects for imaging and laser scanning applications.
In imaging applications, most camera imaging sensors are flat. When optical systems have a flat focal plane, they can produce images that are in-focus across the whole sensor. But when field curvature is present, the plane of focus can only be shifted between the edges of the image and its center.
Single element systems often suffer from field curvature. A field-flattening element like a plano-concave lens can reduce its severity, but in aberrated systems it can create a tradeoff. In this case, worsening distortion.
Field-flatteners best minimize field curvature when other forms of optical aberrations aren’t present. Singlet systems with lots of aberration can be replaced with additional elements to reduce aberration while maintaining a similar effective focal length. With additional aberrations reduced, the addition of a field-flattener effectively eliminates field curvature.
