| 摘要: | 本論文提出一五百萬畫素超大廣角鏡頭設計，由7片玻璃鏡片所組成，鏡頭焦距為1.649 mm，鏡頭長度23.235 mm，F/#為2.1，最大半視角為80，在鏡片優化中我們保持系統的焦距不變之條件下，同時消除色差與消熱差之設計。
考量廣角鏡頭在大視角區域時其影像會有被嚴重壓縮之特性，將傳統的光學畸變評估方式成改以F-theta畸變作為檢視該光學系統的成像扭曲程度。並考量汽車使用之環境溫度範圍，與大視場角相對照度之控制。
不同的鏡片材料有不同的熱膨脹係數，在室溫(T0)條件下鏡片的參數如曲率半徑R，厚度D，以及非球面係數a4、a6、a8，當環境溫度變化(T)時，會因鏡片材料熱膨脹係數影響與溫度改變(T=T-T0)，而改變其鏡片參數如曲率半徑R，厚度D，以及非球面係數a4、a6、a8。故在光學系統在消熱差的條件方面，由光學系統所選擇的玻璃材料的溫度係數(dn/dT)與鏡片熱膨脹係數可推得溫度改變導致的屈光度變化，而當光學系統的屈光度變化不為零時，則可利用鏡筒材料的熱膨脹係數(β)或藉由改變鏡片材料達到消熱差。
在室溫下(20C)單一溫度之鏡頭優化設計，可得鏡頭在空間頻率180 lp/mm 下之MTF至少大於0.57，但在溫度-30C至70C範圍其鏡頭MTF(180 lp/mm)降為0.423以上，而鏡頭MTF最低的位置在室溫70C的環境。最後針對-30C至70C做鏡頭優化設計，我們考量玻璃材料之熱膨脹係數，鏡筒熱膨脹係數，與7片鏡片材料，對於達成無熱化可以得到很好的效果。
最終設計為7片玻璃鏡片，其中含2片非球面鏡片，其鏡頭成像品質在溫度範圍-30C至70C間，MTF(180 lp/mm)至少大於0.597，其MTF變化值在0.597至0.627範圍內。相對照度至少大於89.75%，其相對照度變化值在89.75%至90.53%範圍內。橫向色差至少小於0.851 m，其橫向色差的變化值在0.851 m至0.543 m範圍內。F-theta distortion至少小於0.90%，其F-theta distortion的變化值在0.90%至0.83%範圍內。
;This paper proposed a ultra-wide lens design, which has 5 Mega pixel, and compose of seven glass, the focal length of the lens is 1.649 mm, the total length is 23.235 mm, F/# is 2.1, the maximum of half field-of-view is 80 degree. In the lens optimization we maintain the system′s focal length of the same conditions, While eliminating the design of chromatic aberration and athermal dissipation.
Consider the wide-angle lens in the large viewing area of the image will be severely compressed features, The traditional optical distortion assessment method was changed to F-theta distortion as a view of the degree of imaging distortion of the optical system. And consider the use of the ambient temperature range of the car,and the control of the large field angle relative to the illumination.
Different lens materials have different coefficients of thermal expansion,
at room temperature(T0) conditions, such as the parameters of the lens radius of curvature(R), thickness(D), and aspheric coefficient (a4、a6、a8), when the ambient temperature changes, due to the thermal expansion coefficient of the lens material and temperature changes(T=T-T0), and change the lens parameters. Therefore, in the optical system in the athermal conditions, Therefore, in the optical system in the athermal conditions,the temperature coefficient of the glass material selected by the optical system and the coefficient of thermal expansion of the lens can be used to estimate the diopter change due to the temperature change. And when the dioptric change of the optical system is not zero, you can use the lens barrel material thermal expansion coefficient(β) or change the lens material to achieve athermal.
At room temperature(20C),the single temperature of the lens optimization design, you can get the lens at a spatial frequency of 180 lp / mm MTF at least greater than 0.57,but the lens MTF in the range of -30°C to 70°C is reduced to at least 0.423 ,while the lens MTF has the lowest position at room temperature of 70°C. Finally, for the temperature range of -30 ° C to 70 ° C lens optimization design, we consider the glass material thermal expansion coefficient, barrel thermal expansion coefficient, and 7 lens material, for the realization of athermalized can get very good results.
The final design for the seven glass lenses, which contains two aspherical lenses, lens imaging quality MTF (180 lp / mm) is at least greater than 0.597 in the temperature range of -30°C to 70°C, MTF changes in the range of 0.597 to 0.627. The relative illuminance is at least greater than 89.89%,and the change in relative illuminance is in the range of 89.75% to 90.53%. Lateral chromatic aberration is at least less than 0.851 m, and the change in lateral chromatic aberration is in the range of 0.851 m to 0.543 m. F-theta distortion is at least less than 0.9%, and the change in F-theta distortion is in the range of 0.9% to 0.83%. |
