| 摘要 |
PROBLEM TO BE SOLVED: To provide a rod lens of which the diameter is uniform though being small, to be able to provide a vivid image.SOLUTION: A columnar rod lens has a refractive index continuously changed from the center to the outside and has a radius r, and the refractive index within a range of 0.3r to 0.7r from the center to the outside satisfies formula (1) n(L)=n{1-(g/2)L} where nrepresents a refractive index on the center axis of the rod lens, L (0≤L≤r) represents a distance from the center axis of the rod lens, r represents the radius of the rod lens, g represents a refractive index distribution constant of the rod lens, and n(L) represents a refractive index in a position to which the distance from the center axis of the rod lens is L. The rod lens has a fluorine atom content of 0.1% by mass or more and less than 3% by mass and has the radius r of 100 to 250 μm. |
