| 摘要 |
PROBLEM TO BE SOLVED: To provide an objective lens for picking up light which is composed of a plastic material and in which a focal position change caused by a temperature change is small. SOLUTION: This objective lens for pickup is used of the pickup of an optical system recording and reproducing device, has a single lens, constituted of a plastic material, provided with a brazed grid-shaped refraction surface where a saw-toothed difference is formed in a ring-belt shape on at least one of a first surface 1 or a second surface 2 and satisfies the condition expression of 0.4-(63ψ.λ/NA2)<=ψD/ψ<0.8+(63ψ.λ/NA2), provided that ψ expresses the power of an entire system, ψD expresses the sum of the power of the diffraction surfaces on the first and the second surfaces, λ expresses a wavelength, and NA expresses a numerical aperture on an image side. |
