# Tagged with: Off-axis mirrors

## 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.

## Using the Point Source Microscope (PSM) to find Conjugates of Parabolic and Elliptical Off-axis Mirrors (ABSTRACT)

ABSTRACT: Describes using the Point Source Microscope to find the vertex radius and off-axis distance of off-axis parabolic mirrors by measuring the distance between the sagittal and tangential astigmatic foci and the mirror.

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• 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.

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