Field curvature, also called “Petzval field curvature,” is a defect in
the lens in which the object of a flat plane is not focused on the
image surface. Field curvature measurement is important in lens
performance tests. This paper presents an electrowetting liquid lens
based on the depth from defocus method for measuring field curvature.
This method uses only a pair of defocused images for a patterned flat
object, which are captured using the focus tuning function of the
electrowetting liquid lens. Image processing for calculating field
curvature is carried out using MATLAB. The results of the measurement
experiment demonstrated high accuracy of the 12 µm root mean square
error between the captured image surface and fitted curved image
surface. There is no need for complex equipment such as lasers,
microscopes, and telecentric systems. Because this system has no
mechanical movement for focus tuning, it is simple and shows fast
measurement time compared with other conventional methods.