trifocal

Having three focal lengths.

三焦距的有三个焦距的

Eyeglasses having trifocal lenses.

有三焦距镜片的眼镜

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。

The image is out of focus.

这影像的焦距没调好。

Don't forget to focus the lens.

别忘了调节镜头的焦距。

best image plane of zoom lens

变焦距物镜的最佳像面

focusing glass [ screen ]

【摄】调焦距用的毛玻璃

There are three types of focusing - guesstimate, rangefinder and autofocus .

有三种对焦方式-猜估，用测距仪及自动对焦。

There're three types of focusing guesstimate, rangefinder and autofocus.

有三种对焦方式——猜估，用测距仪及自动对焦。

There are three types of focus- guesstimate, rangefinder and autofocus.

有三种对焦方式??猜估，用测距仪及自动对焦。

For that I want only your face to be in-focus, and the rest of the picture will be out-of-focus.

我只使你的脸在焦距内，其它的在焦距外，

Performance Analysis of the Elliptic Beam Ring-focus Antenna with a Variable Focal Distance

椭圆波束变焦距环焦天线的性能分析

back focal distance

【光】后焦距﹝指镜头与菲林间的距离﹞

equivalent focal length

当量焦距，等效焦距

Focus-to-film distance(f.f.d)

焦点-胶片距离(焦距)

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。

Focus your camera (on those trees).

把照相机的焦距调准（把焦点集中在树上）.

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