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Tagged with: Optical testing

A Model for Cavity Induced Errors with Wavefront Slope in High Accuracy Spherical Fizeau Metrology (ABSTRACT)

A paper by Sykora of Zygo showing that the Random Ball Test (RBT) works less and less precisely as the numerical aperture of the transmission sphere becomes smaller. In other words, the RBT works best for fast transmission spheres and another means of calibration should be used for slow test optics.

A Simple Ball Averager for Reference Sphere Calibrations (ABSTRACT)

ABSTRACT: A paper by authors at NIST about simulations and experiments done with the Random Ball Test (RBT) giving criteria for establishing the precision of transmission sphere calibration using the RBT.

Absolute Measurement of Surface Roughness (ABSTRACT)

ABSTRACT: A paper by Creath and Wyant explaining the method of calibration of surface roughness interferometers. This same method is used in the Random Ball Test (RBT) except that the random surface over which interferograms are averaged is not a plane but a sphere.

Alignment of Optical Systems (ABSTRACT)

ABSTRACT: Describes the advantages of aligning optical systems using a Point Source Microscope (PSM) where the optical axis of the system is folded in 2 or 3 dimensions  and shows how pseudo aberrations can be generated that show quantitatively the degree of precision of the alignment from the Star image seen in the PSM.

Calculation of the Vertex Radius of an Off Axis Parabolic Surface using the Sag Measured with a Three Ball Spherometer (ABSTRACT)

ABSTRACT: A paper by An and Parks describing a method of calculating the vertex radius of an off-axis parabolic segment using a three ball spherometer to measure the sag. The vertex radius is found by solving a set of six simultaneous, non-linear equations for the three coordinates of the ball centers and the corresponding three coordinates of the point of contact of the ball with the parabolic surface.

Calibration of Spherical Reference Surfaces for Fizeau Interferometry (ABSTRACT)

ABSTRACT: A study by Burke and Wu of CSIRO comparing several methods of transmission sphere calibration that concludes the Random Ball Test (RBT) has the highest precision of all the methods tried though it is tedious to perform for highest precision if the RBT is not automated.

Design and Analysis of an Alignment Procedure using Computer Generated Holograms (ABSTRACT)

ABSTRACT: Paper by Coyle describing the use of an autostigmatic microscope (PSM) along with computer generated hologram (CGH) targets for the alignment of optical systems.

Fabrication and Testing of a High-Precision Concave Spherical Mirror (ABSTRACT)

ABSTRACT: Slides by Burke and Wu of CSIRO about Random Ball Test (RBT) calibration of a transmission sphere prior to its use in the test of a high precision hemisphere.

Measuring the Four Paraxial Lens Parameters using an Autostigmatic Microscope (ABSTRACT)

ABSTRACT: Describes using an autostigmatic microscope (PSM) to find the two radii, thickness and index of a singlet lens by making 4 distance measurements similar to those used to measure the radius of curvature of a concave mirror, and then using the 4 distances to iteratively calculate the 4 paraxial lens parameters using an Excel spreadsheet and its Solver application.

Measuring Wedge in a Window (ABSTRACT)

ABSTRACT: One of the easier measurements to make with the Point Source Microscope (PSM) is determining the wedge in a nominally plane, parallel window by removing the PSM microscope objective and using the PSM as an autocollimator to view the wedge between the surfaces.

Non-Contact Probe for On-Machine Metrology (ABSTRACT)

ABSTRACT: On-machine metrology is particularly important for diamond turning and grinding as it is difficult to remount and align a part if it does not meet off-line inspection criteria. There is also the issue of tool wear; a process that started well may fail part way through the cut, and if tool replacement is needed, it is vital to know that before removing the part. A means of rapid, noncontact, in situ profiling and roughness measurement could improve the productivity of diamond tool machining.

Optical Alignment Using the Point Source Microscope (ABSTRACT)

ABSTRACT: A companion paper to "Alignment of an off-axis telescope and prism train" showing more detail of the mechanics involved in the telescope alignment and the multi-sensor instrument package.

Practical Alignment Using an Autostigmatic Microscope (ABSTRACT)

ABSTRACT: This paper defines optical alignment as placing optical conjugates and centers of curvature at the precise locations specified in the optical design. Auto-stigmatic microscopes (ASM) are the tools used to measure the offset between the optical conjugates and physical datums such as centers of balls and axes of cylinders in alignment fixtures and making precise alignment practical.

Case Studies & Testimonials

  • How small can the PSM be used for centering on a cylindrical axis?

    The PSM is an ideal tool for finding the center of curvature of a ball or the axis of a cylinder. The question is for how small a ball or cylinder can the PSM do this?

    The smallest article that was readily available was a piece of monofilament 8 pound test fishing line that was 290 μm in diameter. There was no problem finding the axis of the fishline, and separating the Cat’s eye reflection from the surface from the confocal reflection of the axis. The experiment was done with a 5x objective, and the result would have been even more definitive using a 10x objective.

  • Why is proper alignment so important?

    Here is a case of a very happy customer due to better optics.

    A few days ago an astronomer friend of mine commented that he had gotten the optics of his telescope improved and the improvement reduced the time it took to get data by a factor of 3. For an astronomer this is a dramatic improvement since observing time on large telescopes can cost thousands of dollars an hour.

    My friend did not say how the optics had been improved, but the important point is that better optics, whether due to figure errors, mounting or alignment mean more productive optics. I generally think of better optics as a better product leaving the manufacturing facility without thinking about how much the better optics mean to the productivity of the customer.