With the increasing use of digital cameras in road vehicles, aircraft, head-mounted displays, and security systems, the testing and calibration of cameras targeting distant objects has become essential in development, production, and validation. Whether constrained by the limited space of an optical laboratory or the compact footprint of automated production equipment, the collimator is the inevitable choice for simulating distant targets within a confined physical space.

The principal components of a collimator include a uniform area light source, a test target, and a collimating objective. Owing to material properties and fabrication challenges, large-aperture collimators and those operating in the infrared spectrum often employ reflective optical designs (such as off-axis parabolic mirrors) to eliminate chromatic aberration and achieve broad spectral coverage. For visible-light camera testing, refractive collimating objectives using lenses are more common.

Function of Each Component
Area light source: provides uniform illumination for the transmissive test target.
Test target: provides a reference pattern (such as a checkerboard target, circular edge target, etc.) located at the focal plane of the system, serving as the test object for the device under test (DUT).
Collimating objective: converts the divergent rays emitted from an object point at its focal plane into a parallel beam, thereby simulating imaging conditions at infinity.

Operating Principle
The area light source uniformly illuminates the transmissive test target, which modulates the intensity and spatial distribution of the light beam through its pattern and transmittance. According to the principle of convex lens imaging, rays emitted from an object point at the focal plane are refracted by the lens (or reflected by a parabolic mirror) and emerge as parallel light. To the device under test (DUT), the image of the target formed by the collimator objective is located at infinity, equivalent to an object at an infinite distance. This addresses the problem of simulating a distant target within a confined space.