1.
the ratio of the focal length to the diameter of a (camera) lens system.
相机镜头直径焦距比。
2.
overall f - number
总光圈大小, 总孔径焦距比
3.
A near-sighted eye has a shorter focus than a normal eye.
近视眼比正常的眼睛有较短的焦距。
4.
Having three focal lengths.
三焦距的有三个焦距的
5.
equivalent focal length
当量焦距，等效焦距
6.
Focus-to-film distance(f.f.d)
焦点-胶片距离(焦距)
7.
(geometry) a ratio describing the shape of a conic section; the ratio of the distance between the foci to the length of the major axis.
描述圆锥曲线部分形状的比率；长轴长度与焦距距离比。
8.
autofocus zoom lens
自动聚焦变焦距镜头
9.
variable focal length (cylindrical) lens
变焦(距)(圆柱)透镜
10.
long focus lens
长焦距（望远）镜头
11.
Focal length: The distance between the centre of a lens and its principal focus.
焦距:镜头中心与其主焦点的距离。
12.
The ratio of the focal length of a lens or lens system to the effective diameter of its aperture.
F值物镜或物镜系统的焦距与入射光孔直径之比
13.
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快速变焦距手术显微镜
14.
Only a bit out of focus.
只是焦距有点不对。
15.
One must focus the camera before taking a picture.
拍照之前先要对焦距。
16.
The image is out of focus.
这影像的焦距没调好。
17.
Don't forget to focus the lens.
别忘了调节镜头的焦距。
18.
rear-controlled zoom lens
背面调整变焦距透镜