| 摘要 |
<p>The front-lens attachment has a negative front element stationary relative to the image plane and two lens elements displaceable along the optical axis. The positive lens element adjacent the front element and the negative displaceable lens element cause the imaging scale to change when the focal length is adjusted. The focal length of the negative displaceable lens element and the focal length of the positive displaceable lens element fulfil conditions stipulated by a given formula. The positive lens element can consist of a positively refracting lens, a negatively refracting lens cemented to it and a positively refracting simple lens.</p> |
