Portrait mode chooses a large aperture (a small 'f' number) which will make the depth of field (the amount of your shot in focus) smaller.

人像模式用一个大光圈(f值小)，而让景深(清晰对焦的那部分)变小。

youdao

F is a gradient field. Why?

为什么要说F是一个梯度场？

youdao

We have three conditions, F= so our criterion -- Vector field F equals .

有三个条件，因此我们的标准，向量场。

youdao

The F-35 has already seen plenty of field time in the US, with more than 500 flights already in 2012, and it's set to make its way to the UK armed forces next week and the Netherlands later this year, but while the aircraft is quite familiar to the pilots tasked with flying it, the public hasn't had an opportunity to experience Lockheed's latest airborne warrior.

ENGADGET: Lockheed Martin F-35 Lightning II stealth fighter cockpit demonstrator hands-on (video)