reference:
Aperture 光圈計算
焦段 / 光圈值 = 光圈葉片所需打開的大小
所以定光圈的設計上 所說的定光圈值 實際上就是把光圈的葉片開啟直徑大小給在拉大
ex: 28-70/ constant f2.8
28mm / f2.8 = 10mm , 10mm 級為所需打開的光圈葉片直徑
在70MM焦段位了達成同樣的效果 就必須把 葉片開啟直徑大小給拉大到 70 / 2.8 = 25mm
而光圈值的規算 亮度在級與級之間的差異計算方式為
新光圈值 A, 舊光圈值 a
A = 2的更號2 乘以 a 
EX:
a = f2.8 則 下一級光圈為 f2.8* 1.414= f3.9xxxxx 故為 f4
以下為本解釋的原文:
The size of the opening of an aperture is denoted as Fx.y. Here are a number of examples: F1.4, F2.0, F2.8, F5.6, F8.0, F11.0 and so on. These numbers are usually referred as f-numbers or f-values. The larger the f-number, the smaller/narrower the aperture/lens opening. For example, an aperture F5.6 has an opening smaller than that of F4.0 and F2.8. Hence, by varying the aperture, we can control the amount of light that can reach the image capturing device.
The maximum aperture of 995 is shown on the lens as 1:2.5-5.1. What does this mean? The lens of 995 is a variable-aperture zoom lens. This type of lenses usually has a larger aperture in the short focal length end and a smaller one in the longer focal length end. Since the on-camera lens is 8-32mm (or 38-152mm, 35mm equivalent), this means at focal length 38mm (35mm equivalent), the maximum aperture is F2.5, while the aperture at 152mm is F5.1. As you zoom from 38mm to 152mm, the maximum aperture changes from F2.5 to F5.1.
沒有留言:
張貼留言