Smartphone-based corneal topography with null-screens.

To measure the shape of the fast corneal surface of the human eye, we propose the design and characterization of a compact corneal topographer using the capabilities of a smartphone. The performance evaluation of the compact corneal topographer includes the calculation and compensation of the distortion introduced by the smartphone lens used to acquire the images and the evaluation of a reference surface. To demonstrate the feasibility of our proposal, we performed surface topography measurements on some human corneas and compared the results with those obtained by a commercial corneal topographer.

Testing the surface quality of a reflective parabolic trough solar collector with two flat null-screens.

In this work, we present a technique for quantitatively assessing the optical quality of a parabolic trough solar collector. The presented method is an adaptation of the null-screen technology, a collection of processes that retrieve information from the reflection of a known object from the surface and then use that information to reconstruct the surface's normal vectors. Via numerical simulations, it is shown that the precision attainable by this method is up to 0.

Analytic conic constants to reduce the spherical aberration of a single lens used in collimated light.

We study the formation of caustic surfaces produced by conic lenses, considering a plane wavefront propagating parallel to the optical axis. The shape of the caustic can be modified by changing the parameters of the lens in such a way that if we are able to vanish the caustic, the optical system produces the sharpest diffraction-limited images. Alternatively, caustic surfaces with a large area can be applied to the design of non-imaging optical systems, with potential applications such as diffusers of light for illumination or solar concentrators.

Surface shape evaluation with a corneal topographer based on a conical null-screen with a novel radial point distribution.

In order to measure the shape of fast convex aspherics, such as the corneal surface of the human eye, we propose the design of a conical null-screen with a radial point distribution (spots similar to ellipses) drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact array of circular spots if the surface is perfect. Any departure from this geometry is indicative of defects on the evaluated surface. We present the target array design and the surface evaluation algorithm.

Improving fast aspheric convex surface tests with dynamic null screens using LCDs.

A method for testing fast aspheric convex surfaces with dynamic null screens using LCDs is shown. A flat null screen is designed and displayed on an LCD monitor with drop-shaped spots in such a way that the image, which is formed by reflection on the test surface, becomes an exactly square array of circular spots if the surface is perfect. Any departure from this geometry is indicative of defects on the surface.

Quantitative evaluation of an off-axis parabolic mirror by using a tilted null screen.

We report the testing of a fast off-axis surface based on the null screen principles. Here we design a tilted null screen with drop shaped spots drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact square array of circular spots if the surface is perfect. Any departure from this geometry is indicative of defects on the surface.

Threshold algorithm to recover the deformation of optical surfaces.

The global optimization threshold algorithm is reported to obtain the deformations of an optical surface. The advantage of these types of algorithm is that they can be solved for the correlation problem presented in Seidel polynomials. We obtain the 2D deformations of a surface test with the transversal aberration along one direction only.