With the increasingly widespread application of digital cameras in road vehicles, aircraft, head-mounted displays, security systems, and other applications, camera testing and calibration for distant targets have become essential in camera development, production, and verification. Whether due to the space constraints of optical laboratories or the compact footprint of automated equipment for mass camera production, the collimator has become the inevitable choice for simulating distant targets within a limited physical space.

Structure
The main components of a collimator include a uniform area light source, a test target, and a collimating objective. Due to material properties and manufacturing difficulties, large-aperture collimators and those operating in the infrared band often employ a reflective optical design (such as an off-axis parabolic mirror) to eliminate chromatic aberration and achieve broad spectral coverage. For testing visible light cameras, it is more common to use a lens as the collimating objective.

Functions of Each Component:
Area Light Source: Provides uniform illumination for the transmissive test target;
Test Target: Provides a reference pattern (such as a concentric square target, circular edge target, etc.) located at the focal plane of the system, serving as the test object for the DUT;
Collimating Objective: Converts the diverging light emitted from an object point at its focal plane into a collimated beam, thereby simulating imaging conditions at infinity.

Working Principle:
The area light source provides uniform illumination for the transmissive test target, and the target modulates the intensity and spatial distribution of the light beam through its patterns and transmittance. According to the imaging principle of a convex lens, light emitted from an object point at the focal plane is refracted by the convex lens (or reflected by a parabolic mirror) and exits as a collimated beam. For the device under test (DUT), the image of the target formed by the collimator objective is located at infinity, equivalent to an object at infinity, thus solving the problem of simulating a distant target within a limited space.