| 摘要 |
A collimating magnifier lens which may be used in a head-up display has a focal length of F. The lens has a front part comprising at least one positive element with a focal length between +1 F and +3 F and a negative element with a focal length between -1.2 F and infinity, the focal length of the front part as a whole being between +1 F and +6 F and the negative element of the front part not being cemented to any other element, a rear part comprising a single positive element with a focal length between +0.4 F and +1.2 F, and a field flattener behind the rear part and comprising a single negative element with a focal length between -0.4 F and -1.1 F. The negative element of the front part may have a refractive index less than or equal to 0.13 greater than that of any positive element of the front part and may be meniscus in shape having a focal length of at least 2.8 times that of the positive component and which produces overcorrect spherical aberration. A single positive element with a focal length between +1.4 F and infinity may be used as a middle part. The air gap in front of the rear part is preferably between 0.6 F and 1.1 F, and the air gap between the rear part and the field flattener is preferably between 0.01 F and 0.5 F. The front part of the lens may have two positive elements. A mirror may be interposed in the gap between the rear and front, or rear and middle.
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