Usually one can first meter using a larger aperture (so that the metered exposure time is under 30 seconds), then stop down as necessary and multiply the exposure time accordingly.
The f-stop, otherwise known as the aperture, determines your depth of field (the area in focus) and how much light can pass through the lens to reach the sensor.
f制光圈(或称光圈)决定相机的景深(对焦区域)以及有多少光能通过镜头到达传感器。
3
Each aperture size (referred to as a stop) is marked with a corresponding number that represents half the light of the previous stop.