A new method for testing wide range horizontal field angle

In order to solve the problems of small measurement range, large error and low efficiency of laboratory optical field angle testing, a high-precision, easy -operating, high-efficient, and widely used horizontal field angle test method is proposed. It comes to a conclusion that the test method can reduce the experimental error through the analysis of the principle of the field of view error and the calculation of laboratory simulation. The simulation results show that for cameras with a field of view of more than 150 degrees, the measurement error can be reduced by 37 degrees, and when the field of view of the camera under test is close to 170 degrees, the method can reduce the measurement error by nearly 54 degrees. Meanwhile, a wide-range horizontal field angle measurement method is proposed. The camera under test is moved on the supporting mobile platform to image the target test board, and then the imaging target is read by reading the scale value on the test board calculates the angle of the camera under test. This method can effectively avoid the measurement error of the angle caused by the distance between the center of the lens surface and the center of the entrance pupil, so as to quickly obtain the angle of view test results, and improve the testing accuracy, and it is also suitable for cameras that measure a wide range of field angles (wide-angle camera or fisheye camera, etc.) to solve the problem of laboratory testing a wide range of horizontal field angles.

High-precision Shack-Hartmann wavefront sensing with a multi-focal diffraction Taiji-lenslet array

A Hartmann wavefront sensor is a type of wavefront detection instrument that has been widely used in various fields. Traditional Hartmann wavefront sensors usually comprise a monofocal refraction lenslet array to segment the wavefront at the entrance pupil. Each wavelet is focused at the focal plane along the projection of the lenslet, forming the foci array. Unlike the multifocal self-interference Taiji-lenslet array, a type of multifocal diffraction Taiji-lenslet array was proposed in this study to improve the measurement accuracy using the weighted centroid location algorithm of these multifocal spots, where the latter is more easily designed than the former. An optical experiment was implemented using the multifocal diffraction Taiji-lenslet array to verify its effectiveness. As a type of diffractive lens, a large-aperture Taiji-lenslet array can be easily fabricated via lithography, which has great potential for application in the measurement of large-scale laser beams and optical elements.

Comparison of Camera Calibration and Measurement Accuracy Techniques for Phase Measuring Deflectometry

Phase measuring deflectometry (PMD) is a competitive method for specular surface measurement that offers the advantages of a high dynamic range, non-contact process, and full field measurement; furthermore, it can also achieve high accuracy. Camera calibration is a crucial step for PMD. As a result, a method based on the calibration of the entrance pupil center is introduced in this paper. Then, our proposed approach is compared with the most popular photogrammetric method based on Zhang’s technique (PM) and Huang’s modal phase measuring deflectometry (MPMD). The calibration procedures of these three methods are described, and the measurement errors introduced by the perturbations of degrees of freedom in the PMD system are analyzed using a ray tracing technique. In the experiment, a planar window glass and an optical planar element are separately measured, and the measurement results of the use of the three methods are compared. The experimental results for the optical planar element (removing the first 6 terms of the Zernike polynomial) show that our method’s measurement accuracy reached 13.71 nm RMS and 80.50 nm PV, which is comparable to accuracy values for the interferometer.

Signal of an autocorrelation low-coherence interferometer probing a layered object by a wave-field with wide angular spectrum

The effect of the width of the angular spectrum (numerical aperture) of a broadband-frequency wave-field probing a layered object on the signal of an autocorrelation low-coherence interferometer (ALCI) under spatially coherent and incoherent illumination of the entrance pupil is considered. It is found that under incoherent illumination an increase in the width of the angular spectrum of the field leads to a decrease in the amplitude, a change in the shape and position of the measuring signals of the interferometer due to decorrelation of the object field partial components which have reflected from various interlayer boundaries inside the object. In the case of coherent illumination, the ALCI signal is formed in a confocal mode, which leads to the amplitude extraction of the measurement signals are determined by the mutual correlations between a partial component reflected from the boundary on which the probing field was focused, and partial components of this field which have reflected from other boundaries within the object. This effect makes it possible to determine parameters of the internal layered structure of an object doing without apriori structure-related information. In this case, an increase in the numerical aperture of the probing light beam leads to an increase in the systematic error in determining the optical thicknesses of the layers, which can be estimated on the basis of the obtained expressions.

A model of the appearance of the moving human eye

The entrance pupil and first Purkinje reflection (“glint”) in an image of the human eye serve as important features in 3D, model-based eye tracking applications. Here I present a physically and biologically accurate, ray-traced model that supplies the appearance of the pupil and glint of a moving eye. Once biometrically calibrated for a subject under study, simultaneous fitting of the pupil and glint features by the model supplies eye rotation, radius of the aperture stop, and the translation of the eye relative to the initial camera position. The biometric parameters of the model, including corneal curvature and the depth of the centers of rotation, are obtained by model-based fitting of images of the eye posed at known gaze angles. This approach was applied to eye recordings from 30 people obtained during gaze calibration, and while head position was recorded simultaneously using echoplanar magnetic resonance imaging. The refractive and reflective effects of spectacle and contact lenses worn by some subjects were incorporated into the model. The fitted parameters reveal that the center of rotation for horizontal eye movements is deeper (13.8 mm) than that for vertical eye movements (12.1) mm, consistent with prior studies. Individual differences in the depth of the rotation centers, and in corneal curvature, were well related to biometric measures obtained from these subjects using clinical ophthalmologic instruments. Once biometrically calibrated for each subject, gaze position was modeled with a cross-validated, median (across subject) absolute error of 0.58°, and image-plane translation of the head was estimated with sub-millimeter accuracy. The open-source model described here produces biologically accurate simulations of the appearance of the eye in motion, and may be used in model-based search to derive eye pose and biometric properties from empirical data.