Autocollimator

PRODUCT RANGE AND SPECIFICATION

The Autocollimator is a single instrument combining the functions of a collimator and a telescope. It detects small angular displacements of a mirror by means of its own collimated light.The two reticles are positioned in the focal plane of the corrected objective lens, so that the emerging beam is parallel. This usual configuration is known as infinity setting, i.e the autocollimators are focused at infinity.When moving the reticles out of the focal plane of the objective lens, the autocollimator can be focused at finite distances, and the beam becomes divergent (producing a virtual image) or convergent (real image). This results in a focusing autocollimator. The shape of the beam -convergent or divergent-depend on the direction in which the reticles are moved.

CONSTRUCTION

The main components of a standard autocollimator i.e. focused at infinity are:

• Tube mounted objective lens

• Beam splitter mount which contains two reticles

• Eyepiece

• Illumination device

The illuminated reticle projected over the beamsplitter towards the lens is known as collimator reticle. The second reticle placed in the focus of the eyepiece is the eyepiece reticle.The beamsplitter mount together with the eyepiece and the illumination device form a main unit called: Autocollimator Head.A focusing autocollimator (finite disatnce setting) is similary built. The autocollimator head containing the two reticles is now mounted on a draw out tube for focusing adjustment.

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OPERATING PRINCIPLE

Autocollimation is an optical technique of projecting an illuminated reticle to infinity and receiving the reticle image after reflection on a flat mirror. The reflected image is brought to the focus of the objective lens in which the eyepiece reticle is located. Thus the reflected image of the collimator (illuminated) reticle and the eyepiece reticle can be simultaneously observed. 

When the collimated beam falls on a mirror which is perpendicular to beam axis, the light is reflected along the same path. Between the reflected image and the eyepiece reticle which are seen superimposed, no displacement occurs.

If the reflector is tilted by an angle α the reflected beam is deflected by twice that angle i.e. 2α. The reflected image is now laterally displaced with respect to the eyepiece reticle.

The amount of this displacement „d“ is a function of the focal length of the autocollimator and the tilt angle of the reflector: d=2αf. (α in radians). 

The tilt angle can be ascertained with the formula: where „f“ is the effective focal length EFL of the autocollimator. Since the „f“ is a constant of the autocollimator, the eyepiece reticle can be graduated in angle units and the tilt angle can be directly read off.

Standard Autocollimators

Infinite settings

	The available beam splitter mounts are of different types: Standard beam splitter mount including two reticles at choice.
	RC – Beam splitter mount with illuminated reticle changer (4 positions for collimator reticles) and one eyepiece reticle. Five reticles at choice are included.
	RC/FC – Beam splitter mount with illuminated reticle changer. Filter changer with 4 positions. One green and one white diffuser are included. Further filters on request.
	Large field beam splitter mount including two reticles at choice.