The working principle of optical autocollimator
Sep. 19, 2020
The optical autocollimator is designed based on two basic optical principles: the collimation principle of light and the reflection principle of the beam by the plane mirror. The autocollimator projects the image in a form of a parallel beam (collimated light) onto a mirror, which reflects its beam back to the autocollimator to form an autocollimated image. If the mirror is perpendicular to the optical axis, the beam will reflect back to itself.
There are three types of optical systems for optical autocollimators, Gaussian system, Abbe system and integrated system.
The light path of gaussian system includes light source, condenser, beam splitter, reticle, collimator, optical reflector and eyepiece. In order to prevent the eyepiece from being blocked by the light source, the optical path of the autocollimator is equipped with a spectroscope on the optical axis. Cube prism can be used as the spectroscope. The optical design can also be that a spectroscope (cube prism) is placed in front of the objective lens group, so that the objective lens has two conjugate focal planes due to its light splitting. One focal plane is placed on the cross-line reticle and illuminated by the light source. The other focal plane is placed on the double-reticle. The optical path separates the self-collimated image from the original reticle and avoid blind areas.
The advantage of the Gaussian system is, the field of view is not blocked by the light source, the reticle can be located in the center of the field of view, and the measurement range is relatively large. The disadvantage is that the loss of high brightness is relatively large. A large amount of brightness is lost every time through the spectroscope.
The Abbe system uses part of a focal plane for the collimator tube and part for the eyepiece group. The optical path includes right-angle prisms, optical lenses, optical mirrors and reticles. The main advantage of the Abbe system is high light intensity and low brightness loss. But due to the glued prism, the field of view will be blocked.
The integrated system includes the advantages of the Gaussian system and the Abbe system, with no obstruction of the field of view and low brightness loss. The optical path includes optical lenses, condenser, optical reflector and reticle.
The optical autocollimator is mainly used to measure angle and parallelism. It can also measure some parameters of optical components. For example, the angle between the wedge and the parallel plate, the angle of prism, and the spherical radius of the concave and convex optical components.
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