| 摘要 |
PROBLEM TO BE SOLVED: To obtain a compact photographing lens with high resolution and a small number of components. SOLUTION: The lens is composed of an arrangement of a first lens L1 as a negative lens nearest to the object, apertures S1 and S2 with air gaps, a second lens L2 as a positive lens with a small air gap, a third lens L3 as a negative lens with an air gap, a fourth lens L4 as a positive lens and a fifth lens L5 as a positive lens with a small air gap. The lens constitutes a retro-focus type with the diverging effect of the first lens L1 and the condensing effect of the second lens L2 to the fifth lens L5 backward from the apertures S. Lithium niobate which is a material having a high refractive index (nd>2.0) is used for an optical low-pass filter to reduce the length of the back focus in the photographing optical system in which the above lens is disposed.
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