Measurement parameters of optical lens and principle of optical parameters

First, the measurement of the radius of curvature

The radius of curvature is one of the most important indicators reflecting the information of a single spherical surface, and it is also a direct parameter that needs to be controlled in spherical surface processing. The machining control accuracy of the radius of curvature directly affects the focal length of the lens and other functional indicators.

The traditional curvature radius measurement is based on template control, which requires a template to be made in advance and increases the risk of damaging the processed lens. Now many optical lens manufacturers have gradually replaced the traditional measurement method with non-contact non-destructive measurement methods. Fully automatic measurement, simple and convenient operation, high measurement efficiency.

The radius of curvature is measured using the reflective state. The high-quality CCD camera respectively focuses on the optical lens surface and the center of curvature, and the focusing position is accurately calculated by the test r software on the cross-wire image and grating scale data collected by the CCD. The imaging position of the surface image and the central image of the meniscus lens, the radius of curvature of the lens to be measured is equal to the distance between the two positions.

Second, the measurement of focal length

The focal length is one of the important lens design indicators. Although it cannot be directly controlled in the processing process, it reflects the comprehensive information of each surface including curvature, material, thickness, etc. The accuracy of the focal length directly affects the actual function of the lens. The accuracy of the focal length directly affects the actual function of the lens. According to different calculation positions, the focal length can be divided into effective focal length (EFL), back focal length (BFL) and front focal length (FEL). Its measurement principle is slightly different.

The principle of focal length measurement:

Effective focal length is the distance from the optical principal plane to the corresponding focal point. The measurement method is the transmission mode. The measurement wavelength adopts cold light source, double vertical crosshairs, collimator, lens under test, achromatic objective lens and photoelectric self-collimating objective lens. A double vertical line image is formed on the CCD. The measurement software controls the motorized translation stage to accurately focus the image and automatically calculates the focal length of the special measurement lens based on the collected images.

The front and rear focal lengths are the distances from the vertex of the optical surface of the lens to the corresponding focal point. The measurement method is similar to the measurement of the radius of curvature. The detection components of the system focus and image the lens surface (reflection method) and focal plane (transmission method), respectively, and test the focus position. The software can calculate the reticle image and raster rule data collected by the CCD with front and rear focal lengths equal to the distance between the two positions.

When measuring the focal length, the operator needs to select the top of the "Focal Length Measurement" software, and select the lens and reticle type according to the range of the focal length of the lens to be measured, then adjust the position of the photoelectric autocollimator, and find a clear double image on the screen. You can get the focal length value of the vertical line cross-wire image, and the true result will be displayed in the display box in sequence.

3. Measurement of center deviation

Eccentricity (or center deviation) plays an important role in lens assembly and application function. The eccentricity of a lens (or lens group) refers to the deviation of the position or direction of the optical axis from the reference axis when the optical axis is not aligned with the reference axis. The eccentricity of a lens (lens group) is usually measured by rotating the sample. By adding a certain lens rotation device, the comprehensive measuring instrument can also be used as a high-precision eccentricity measuring instrument.

In addition, there are also instruments for central deviation that are very targeted for measurement:

High-precision cylindrical lens eccentricity measuring instrument: an instrument mainly used to test the relevant indicators of the center deviation of cylindrical lenses, and also suitable for transflective measurement of the center deviation of rectangular spherical lenses.

Digital lens eccentricity measuring instrument: a precision measuring instrument for the center deviation of the optical lens group with large size and multiple lenses, equipped with a high-precision air-floating rotary table to drive the lens group to rotate smoothly, so as to realize non-contact measurement.

Double optical path center deviation measuring instrument: more suitable for infrared lens or lens assembly with lenses installed at both ends

4. Comparative measurement of angular accuracy

The measurement principle also adopts the principle of collimating light pipe. The crosshairs illuminated on the focal plane of the collimating lens are projected to infinity, reflected by the mirror, and then imaged by the collimating lens on the photosensitive surface of a high-precision CCD industrial camera. Small changes between the autocollimator's optical axis and the mirror angle will cause a deviation in the cross-image position, which the system translates into the angular value that needs to be measured.