| 摘要 |
PURPOSE:To reduce the weight of a focusing group by satisfying 0.15<l/f<0.25, 0.7<fR/f<0.9, and 0.4<Hex/Hin<0.6 when performing focusing operation by a rear-group extension system. CONSTITUTION:When focusing operation from infinite distance to short distance is carried out, a rear group GR is moved along the optical axis and focused. At this time, 0.15<l/f<0.25, 0.7<fR/f<0.9, and 0.4<Hex/Hin<0.6 is satisfied. Here, (l) is the air gap between a front group GF and the rear group GR, (f) is the focal length of the whole system, fR is the focal length of the rear group GR, and Hin and Hex are the height where a rand light of the highest incidence height passes through the 1st surface of the rear group GF and the height where the light beam exists from the final surface of the rear group GR. Consequently, while a relatively wide view angle and brightness are maintained, an excellent image is obtained.
|
