| 摘要 |
A small super-wide angle optical system is provided to secure a super-wide angle range and a short total length by positioning a first lens group with strong negative refractive force in the front side of an iris. A small super-wide angle optical system is composed of a first lens group having a first lens(L1) having the negative refractive force and a second lens(L2) having the positive or negative refractive force, which are disposed in order from an object, and having the negative refractive force in general; a second lens group having a third lens(L3) having the positive refractive force; a third lens group comprising having a fourth lens(L4) having the positive refractive force and a fifth lens(L5) having the negative refractive force, which are arranged in order from the object, and having the positive refractive force in general; and an iris installed between the first and second lens groups. The first lens group, the iris, the second lens group, and the third lens group are aligned in order from the object. The first and second lens groups satisfy the following condition, 0.4<Phi12/Phit<0.8, where Phi12 is the reciprocal of the total focal distance of the first and second lens groups, and Phit is the reciprocal of the total focal distance of all the lenses.
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