1.
back focal distance
【光】后焦距﹝指镜头与菲林间的距离﹞
2.
inverted telephoto lens =retrofocus Iens
广角镜头之一种(扩大后组焦距的设计)
3.
retrofocus lens = inverted telephoto lens
广角镜头之一种，扩大后组焦距的设计
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.
adjust the rear mirror, the focus of a camera, the sights of a gun
调准后视镜、 照相机的焦距、 枪炮的瞄准器
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.
F"J6Rf%H'P*Qo?D~z;RC F[v
快速变焦距手术显微镜
13.
Only a bit out of focus.
只是焦距有点不对。
14.
One must focus the camera before taking a picture.
拍照之前先要对焦距。
15.
The image is out of focus.
这影像的焦距没调好。
16.
Don't forget to focus the lens.
别忘了调节镜头的焦距。
17.
rear-controlled zoom lens
背面调整变焦距透镜
18.
best image plane of zoom lens
变焦距物镜的最佳像面