Design Of Ultra-short Focus 4K Projection Lens Based On DLP System

Projection display technology is a typical representative of modern optical imaging.With the development of science and technology and people’s continuous pursuit of better visual experience,the popularity of 4K projector has become a general trend.While the projection system pursues the development of large screen,high resolution and high image quality,it also hopes that the projection system can occupy a smaller space.Ultra-short focal projection system can break through the limitation of space environment,realize the projection of super-large screen at ultra-short projection distance,and can maintain excellent image quality.Based on the DLP system design of ultra short focal 4 k projection lens,the light path structure of fold reflex,contains only 14 pieces of lens refraction lens group,including four pieces of aspherical glass lenses,two sets of double agglutination lens,aspherical reflector adopts accidentally time,can be in in the projection distance of 460 mm,like surface can still achieve 80 inches,projection ratio as low as 0.26,The f-number is 2.2 and the resolution is 4K.The main research scheme of the design process is as follows:1)To modern projection technology development and research status at home and abroad were summarized,analyzed and compared the existing ultra short focal the advantages and disadvantages of three kinds of structure form of the projection lens,on the basis of the refraction and reflection type mix of fold reflex the light path structure,and analyzed from the principle of this kind of fold reflection type structure of ultra short focal lens under the wide field to solve field control,calibration problem.2)According to the design index formulated by the company where the practice base is located,and based on the previous PW method,the appropriate initial structure is selected,which is improved and optimized in ZEMAX according to geometrical optics,aberration theory and other relevant principles.The RMS value of the final design result is less than the single pixel size of DMD chip,MTF is greater than 0.6 at 94 LP /mm cutoff frequency,far exceeding the design index 0.3,and relative illuminance is more than 85%,horizontal TV distortion is less than 0.15%,vertical TV distortion is less than 0.1%.The vertical axis color difference is less than half a pixel size of DMD chip.3)Tolerance analysis and improvement schemes were developed.Sensitivity analysis of the system was carried out according to the existing manufacturing,processing and assembly accuracy.According to the analysis results,a tolerance item was improved or tightened appropriately for the optical structure,and the risk assessment of sensitive tolerance items was conducted.The final Monte Carlo analysis results show that at the 94 LP /mm cutoff frequency,the average MTF of all fields of view is greater than 0.441 in 90% of cases,which can meet the imaging requirements of ultra-short focal projection lens.