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.
Recently, a planoconvex structure electrowetting lenticular lens capable of 2D/3D conversion through a varifocal property by an electrowetting phenomenon has been developed. However, even though it has a similar planoconvex structure to that of a commercial solid lenticular lens, comparable 3D performance could not be realized because the refractive index difference between nonconductive liquid and conductive liquid was not large. Therefore, the goal of the present study is to obtain better 3D performance compared to the conventional planoconvex structure by introducing a novel biconvex structure using ETPTA. The newly developed biconvex structure electrowetting lenticular lens showed greatly improved characteristics compared to the planoconvex structure: dioptric power (171.69D → 1,982.56D), viewing angle (26degrees → 46degrees), and crosstalk ratio (27.27% → 16.18%). Thanks to these improvements, a fine 3D image and a natural motion parallax could be observed with the biconvex structure electrowetting lenticular lens. In addition, the novel biconvex structure electrowetting lenticular lens was designed to achieve a plane lens state with a no voltage applied condition, and as such it could show a clean 2D image at 0 V. In conclusion, a novel biconvex structure electrowetting lenticular lens showed 2D/3D switchable operation as well as excellent 3D performance compared to a solid lenticular lens.
Depth from defocus (DFD) obtains depth information using two defocused images, making it possible to obtain a depth map with high resolution equal to that of the RGB image. However, it is difficult to change the focus mechanically in real-time applications, and the depth range is narrow because it is inversely proportional to the depth accuracy. This paper presents a compact DFD system based on a liquid lens that uses chromatic aberration for real-time application and depth accuracy improvement. The electrical focus changing of a liquid lens greatly shortens the image-capturing time, making it suitable for real-time applications as well as helping with compact lens design. Depth accuracy can be improved by dividing the depth range into three channels using chromatic aberration. This work demonstrated the improvement of depth accuracy through theory and simulation and verified it through DFD system design and depth measurement experiments of real 3D objects. Our depth measurement system showed a root mean square error (RMSE) of 0.7 mm to 4.98 mm compared to 2.275 mm to 12.3 mm in the conventional method, for the depth measurement range of 30 cm to 70 cm. Only three lenses are required in the total optical system. The response time of changing focus by the liquid lens is 10 ms, so two defocused images for DFD can be acquired within a single frame period of real-time operations. Lens design and image processing were conducted using Zemax and MATLAB, respectively.
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