Do you know what types of field mirrors there are?

Field mirrors can be divided into flat field mirror (f-theta) lens and telecentric lens according to their functions. Telecentric lens is mainly designed to eliminate phase difference. It can keep the image magnification unchanged within a certain object distance, which is a very important application when the measured object is not on the same object plane. Telecentric lens is mainly used in machine vision where lens distortion is highly required. Therefore, flat field mirror is mainly used in laser marking machine in industrial application.

Flat field mirror lens

For monochromatic light imaging, the image plane is a plane, and the image quality on the whole image plane is consistent, the aberration is small, and there is no vignetting. For a certain incident light, the deflection speed corresponds to a certain scanning speed, so the linear scanning can be realized by the incident light with equal angular speed. The deflection position of the incident beam is generally placed at the focus in front of the object space. The main light of the image square is parallel to the optical axis, which can achieve the consistency of image quality on and outside the axis to a great extent, and improve the illumination uniformity. It is widely used in the laser marking system, which will produce off-axis deflection, and there will be abnormal image or distortion on the marking surface compared with the ideal plane. The purpose of flat field mirror lens is to form a uniform focusing spot in the whole marking plane. It is one of the most important accessories of laser marking machine. Due to the high cost and expense of telecentric lens, f-theta lens is mainly used in industrial laser marking machine. Without deformation, the position of the focus depends on the focal length of the lens and the tangent of the deflection angle, and the position of the focus depends only on the focal length and deflection angle, which simplifies the calculation method of focus positioning.

Telecentric lens

Telecentric lens is specially designed to make the main light of the focused beam perpendicular to the focal plane at any field angle by making the entrance pupil of the system at the front focus position of the lens system. In the system, the entrance pupil position refers to the position where the beam deflects from the optical axis. In a uniaxial system, the entrance pupil is located at the lens; In a biaxial system, it is located in the middle of two galvanometers.

The telecentric optical path is divided into object telecentric and image telecentric. The principle of object telecentric is that the aperture light barrier of the system (the aperture in the camera) is imaged at infinity by the lens in front of it, so the main light is parallel to the optical axis. As a result, when the object moves back and forth, the image points on the image plane will only be blurred and the position center of gravity will remain unchanged. Telecentric optical path is most commonly used in precision measurement system using imaging principle. The index to measure the telecentric optical path is telecentricity. Because the main light of the object is parallel to the optical axis, the lens aperture is large and larger than the object field of view.

The main technical parameters considered in the selection of field mirror are working wavelength, incident pupil, scanning range and focusing spot diameter.