DAVIDSON OPTRONICS How to Use an Autocollimator to Measure the 90 degree angle of a Cube

MEASURE THE 90° ANGLES OF A HIGH PRECISION CUBE

Prior to measuring a cube's angles, the optical axis of an autocollimator such as the Model D-638, Coordinate Autocollimator must be set parallel to an optical bench as described in the previous How to Align an Autocollimator to an Optical Bench application note.

Using an autocollimator to measure the 90 degree angle of a high precision cube

Figure 1. Using an autocollimator to measure the 90 degree angle of a high precision cube

The steps needed in order to accomplish this task are as follows:

Clean the bench or the plane that the cube will be set upon thoroughly to remove any small pieces of dirt and/or dust. Dirt and/or dust will alter the angle results and they may also scratch the faces of the cube.

The cube may be either coated or uncoated. The face of the cube that is looking into the autocollimator and the face of the cube that is resting on the glass plate should be polished.

Set up the cube on the same plane used to align the autocollimator with the parallel-sided mirror and rotate the cube until the return image can be seen through the autocollimator's eyepiece.

The elevation error read in the autocollimator is the deviation of the cube's angle from a perfect 90°.

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