| 摘要 |
PROBLEM TO BE SOLVED: To correct a spherical aberration of an optical system complementarily, use a resin lens and make an apparatus compact, light-weight and low-cost, by constituting so that a change of an index of refraction per unit temperature and a numerical aperture of a collimator lens and an objective lens satisfy predetermined conditions. SOLUTION: When a temperature rises and if a collimator lens 2 and an objective lens 4 are formed of resin, an index of refraction of each lens decreases, a focal point of the collimator lens is separated from a position of a light source, specifically, moved from Of to Of', an output light changes from a parallel light 3 to a scattering light 6, and a condensed point becomes 7. On the other hand, a focal point Of' of the objective lens 4 comes close to 7 due to the decrease of the index of refraction. Supposing that indices of refraction per unit temperature of the collimator lens and objective lens are nc, nb and numerical apertures of the lenses are NAc, NAb, respectively, nb<=nc<=5nb, 0.8<=NAc<=0.4, 0.45<=Nab<=0.75, 0.25(NAc.nc)/(NAb.nb)<1.5 are satisfied, so that a spherical aberration is almost eliminated. |
