What is a Field Microscope?
The field of view is also called the field of view in optical engineering. The size of the field of view determines the field of view of the optical instrument. The field of view can be represented by FOV, and its relationship with focal length is as follows: h = f * tan \ [Theta]; image height = EFL * tan (half FOV); EFL is the focal length; FOV is the field of view.
1. In optical instruments, take the lens of the optical instrument as the apex,
The field of view is divided into the object-side field of view and the image-side field of view. Concerns for users of general optical equipment
Standard lens: The angle of view is about 45 degrees, and the range of use is wide.
Today, LEDs are widely used in various fields, such as road lighting, projectors, and indoor lighting, due to their long life and low energy consumption. In many applications, the distance between the illuminated target surface and the light source and the field of view of the light beam are not fixed. For example, infrared lighting equipment used in night surveillance systems needs to be able to change its own The field angle and energy density distribution make its irradiation range cover the entire monitoring area. If the field angle of the infrared lamp is too large, it will cause waste of light energy, otherwise it will produce a flashlight effect and affect the lighting effect. To meet this application requirement, it is necessary to design an LED illumination optical system with a variable field of view. [3]
Conventional variable viewing angle illumination optical systems often use two or three lenses to distribute light Figure 4 2D structure of total reflection lens
There are several problems with this form. Most infrared emitting diodes have a half-field angle of about ± 60 °, similar to the Lambertian distribution. The use of a multi-lens form inevitably prevents large-angle beams from being collected and utilized, resulting in a waste of light energy. Because the number of lenses is often more than one, the volume of the system is relatively large. The traditional lens structure has a low degree of freedom in design. The structure designed for one or two modes only works well in this mode, and its beam uniformity decreases significantly after deviation. In response to these problems, this paper uses a new type of total reflection (TIR) lens structure to replace the traditional structure to achieve variable field angles. According to the different requirements of the light intensity distribution of the beam collimation mode and the maximum field angle mode, based on the separation variables The design theory of non-imaging optical system designs its transmission surface and total reflection surface respectively. Because the transmission surface and the total reflection surface of the new total reflection lens adopt the form of free curved surface, which has a high degree of design freedom, it can better consider each field of view and keep the entire field of view angle change process high Light energy utilization and beam uniformity, and the overall structure is compact, easy to install and adjust.
Field of View Design Method
Figure 4 shows the 2D structure of the new total reflection lens. The black rectangle indicates the LED. AB, Figure 5 3D view of a total reflection lens
BC, CD, and EF are straight lines, and DE and FG are free curves. CD is the lens base, and the length is denoted as t. P 1 P 2 represents the moving range of the LED during the change of the viewing angle, and the length is denoted as 1. When the LED is located at P 1 , the optical system is in a collimation mode, and when the LED is located at P 2 , the optical system is in a maximum field angle mode. represents the included angle between the LED emitted light and the optical axis. 1 represents the angle between P 1 B and the optical axis, that is, the critical value of the beam angle assigned by the transmission surface and the total reflection surface in the collimation mode. 2 represents the angle between P 2 B and the optical axis, that is, the critical value of the beam angle assigned by the transmission surface and the total reflection surface in the mode of maximum field angle. The transmissive surface is designed based on the collimated emission of the light beam when the LED is located at the position P 1 , and the total reflection surface is designed uniformly according to the total emitted light beam when the LED is located at the position P 2 . In the design process, LED is considered as an ideal point light source.
Field of View System Simulation
According to the above method, a new total reflection type with a field of view angle change range of 8 ° to 20 ° is designed. Figure 6 Ray tracing diagrams in (a) collimation and (b) field of view maximum modes
The main technical parameters of the lens are shown in Table 1. After the design is completed, UG software is used for 3D structural modeling, as shown in Figure 5. In the process of LED moving, the system's light energy utilization rate is between 80% and 85.8%, and the irradiance uniformity is between 77.3% and 89.3%. Take the average of the three modes to measure the optical performance of the entire zoom process of the system. The average light energy utilization rate is 83.7%, and the average irradiance uniformity is 84.1%. A conventional lens structure that also achieves a range of field angle variation of 8 ° to 20 ° is used as a comparison. The traditional optical system uses a two-lens structure, of which the former is a standard spherical lens. Table 1 Optical design parameters
With the freedom of design, the rear surface of the rear lens is designed as an even aspheric surface. The ray tracing diagram is shown in FIG. 6.
Simulate the irradiance distribution on the target surface at 10 m at 20 °, 14 ° and 8 ° beam angles. Compared with the new total reflection structure proposed in this paper, the results are shown in Table 2. Achieve the same range of FOV from 8 ° to 20 °. The traditional structure system has a total length of 40 mm and a diameter of 44 mm. The system structure using a new total reflection lens has a total length of 13.5 mm and a diameter of 26 mm. 1/5 of the structure. The average light energy utilization rate of the traditional structure in three fields of view is 70.2%, while the new structure Table 2 Performance comparison results
The average light energy utilization rate of the structure is 83.7%, which is about 13% higher than that of the traditional structure. It can be seen from Table 2 that the irradiance uniformity of the traditional structure is high when the field angle is small, but the uniformity decreases rapidly after the field angle becomes larger. . Although the uniformity of the new structure is not as good as that of the traditional structure at a small field of view, the uniformity remains above 75% during the entire zooming process, and the average uniformity is about 17% higher than that of the conventional structure. Considering the entire process of changing the viewing angle, the system using the new total reflection lens structure always maintains high light energy utilization and uniformity of irradiance, and it is compact and easy to install and adjust, so its overall effect is better than traditional Lens structure.
Field of View Study Conclusions
A design method of LED illumination optical system with variable field of view is proposed. The total reflection lens structure is adopted. According to the different requirements of the light intensity distribution in the alignment mode of the optical system and the maximum field angle mode, the transmission surface and the total reflection surface are respectively designed, and the total reflection surface is optimized based on the simulation results. Finally, a comparative analysis is performed under the same conditions as the conventional lens structure, and the simulation results show that the structure is superior to the traditional structure in terms of light energy utilization rate and irradiance uniformity. And the optical system contains only one lens, which is more compact and easy to adjust. [4]
