Lens centration is the relationship between a lens’s optical axis and a defined reference axis, such as the lens edge, a mounting cell, or the optical axis of another lens. A centration error occurs when these axes differ in position or direction.
Precise centration and alignment are critical for maintaining the intended image quality of an optical system. Centration errors can occur during the production, cementing, bonding, and adjustment of lenses and lens assemblies.
What causes centration errors?
Centration errors can occur at different stages of manufacturing and assembly. They may result from the position or tilt of a lens, errors introduced during cementing or bonding, or misalignment between optical elements and their mechanical reference axes.
For complex lens assemblies, it may be necessary to evaluate the position and orientation of multiple optical surfaces relative to a common reference axis.
What needs to be measured?
Depending on the lens and application, centration measurement can include:
* Translational displacement of a lens
* Lens tilt
* Surface tilt error
* Cementing error
* Tilt of an aspherical axis
* Air gaps and center thickness
For assembled lens systems, measurement can also be used to determine the optical axes of individual lenses, lens groups, or the complete optical system.
How is lens centration measured?
A typical centration measurement requires the lens to rotate around a precise reference axis. Measurement can be performed in reflection or transmission, depending on the lens and measurement requirements.
In reflection measurement, an autocollimator observes the image reflected from the lens surface as the lens rotates. A centration error produces a circular movement of the observed image, from which the error can be determined.
When is measurement not enough?
In production environments, identifying a centration error may be only the first step. If the lens needs to be positioned relative to a defined optical or mechanical axis, an alignment process can be used to correct the position and orientation before cementing or bonding.
This is particularly relevant when assembling high-performance optical systems, where consistent alignment between individual elements is important.
A solution for lens centration and alignment
OptiCentric® from TRIOPTICS is one example of a system designed for high-precision centration testing, lens alignment, cementing, and bonding. Depending on the configuration, OptiCentric systems can handle spherical, aspherical, and cylindrical lenses and lens assemblies across UV, VIS, and IR applications. The systems can achieve measurement accuracy of up to 0.1 µm. Need help selecting the right optical metrology solution? Prolog Optics can help evaluate your application requirements and identify a suitable solution.