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How to Calibrate an Autocollimator

An autocollimator is an optical instrument used to align the various movable components in optical or mechanical systems. It works by projecting an optical image onto a mirror, and measuring the degree by which the image that is returned is deflected from its expected position. Autocollimators need to be calibrated before they are used in order to ensure accuracy. However, the only reliable way to calibrate an autocollimator is to measure deflection of an image through controlled angles.

Things You'll Need

Autocollimator
Test reticle
Flat mirror
Table-mounted c-clamp
Protractor
Ruler

Instructions

- 1
  Mount your autocollimator on a flat table surface parallel to the edge of the table.
- 2
  Mount your c-clamp to the corner of the table constituted by the edge on which you mounted your autocollimator. Make sure your autocollimator is facing the c-clamp.
- 3
  Place your mirror inside your c-clamp tilted at a 45-degree angle relative to the tabletop, with its reflective surface facing both the autocollimator lens and the table. Loosely tighten the c-clamp around the sides of the mirror and make fine adjustments to your angle by measuring with the protractor. Make sure that the mirror's surface is exactly 45 degrees relative to the top of the table, and tighten the c-clamp.
- 4
  Measure the circumference of the image in your test reticle -- a pattern or grid placed in the eyepiece to provide scale -- with your ruler and place it inside the autocollimator's lens.
- 5
  Shine the autocollimator at the mirror and the test reticle's image will be reflected down onto the table top. Measure its circumference. If it is equal to the circumference measured in Step 4, your autocollimator is properly calibrated. If not, make fine adjustments to the vertical and horizontal positioning dials adjacent to the housing of the autocollimator's lens and try again until it is.

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