1.
Focus-to-film distance(f.f.d)
焦点-胶片距离(焦距)
2.
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。
3.
The flatter the ellipse, the farther apart are the foci, and the farther each focus is from the center .
椭圆越扁平，两焦点之间的距离越远，每个焦点离中心的距离也越远。
4.
Eyeglasses having trifocal lenses.
有三焦距镜片的眼镜
5.
Having three focal lengths.
三焦距的有三个焦距的
6.
equivalent focal length
当量焦距，等效焦距
7.
Only a bit out of focus.
只是焦距有点不对。
8.
back focal distance
【光】后焦距﹝指镜头与菲林间的距离﹞
9.
coincidence range finder
复合焦点测距仪，叠象测距仪
10.
macro teleconverter
增距式微距附加镜﹝使标准镜头变成微距而保留最近封焦距离﹞
11.
autofocus zoom lens
自动聚焦变焦距镜头
12.
variable focal length (cylindrical) lens
变焦(距)(圆柱)透镜
13.
long focus lens
长焦距（望远）镜头
14.
Discussion about Off-Focus Influence on MTF for Long Focus Aerial Camera
长焦距航天遥感相机离焦对传递函数的影响
15.
Attach the infrared filter and focus on the subject. Read the indicated distance off the lens barrel.
按上红外线滤光片,对拍摄景物对焦,请读出镜头筒指示的距离。
16.
Bring the object into focus if you want to take a good photograph
你想拍一张好照片，就得对准焦距。
17.
You cannot take a good photograph unless the object is in focus.
只有对准焦距才可以拍出好照片。
18.
Focus your camera (on those trees).
把照相机的焦距调准（把焦点集中在树上）.