bravergu5 发表于 2018-11-12 22:46

每两档之间的数值关系是“根号二”倍，就是1.414，这是理论值，实际中使用的光圈值是约等于的整数或者一位小数。
光圈值的序列如下
1-1.4-2-2.8-4-5.6-8-11-16-22-32
可以看出，每间隔一个，之间的关系是两倍的关系。
so，F1到F1.4是一整档，F1.2和F1.4差1/2档。

何时何地 发表于 2018-11-12 21:50

楼主中学数学过了么？

潇杨666 发表于 2018-11-12 22:06

版主说的1.2比1.4大三分之一光圈（实际0.36） 完全没毛病
而楼主T-STOP值：0.4448 也没毛病

只不过两着比较的基准不同，
版主说的是 1.2比1.4大多少的问题
楼主说的是 1.2和1.4 T-STOP 也可以说“档” 的差异[/color]

何时何地 发表于 2018-11-12 21:50

楼主中学数学过了么？

camson 发表于 2018-11-12 18:58

T-STOP要引进来，就复杂了。研究太多没用。够用就行。

T-stop

A T-stop (for transmission stops, by convention written with capital letter T) is an f-number adjusted to account for light transmission efficiency (transmittance). A lens with a T-stop of N projects an image of the same brightness as an ideal lens with 100% transmittance and an f-number of N. A particular lens' T-stop, T, is given by dividing the f-number by the square root of the transmittance of that lens:

{\displaystyle T={\frac {f}{\sqrt {\text{transmittance}}}}.} T={\frac {f}{\sqrt {\text{transmittance}}}}.
For example, an f/2.0 lens with transmittance of 75% has a T-stop of 2.3:

{\displaystyle T={\frac {2.0}{\sqrt {0.75}}}=2.309...} T={\frac {2.0}{\sqrt {0.75}}}=2.309...
Since real lenses have transmittances of less than 100%, a lens's T-stop number is always greater than its f-number.[7]

With 8% loss per air-glass surface on lenses without coating, multicoating of lenses is the key in lens design to decrease transmittance losses of  ...

camson 发表于 2018-11-12 18:45

也学习了下。感觉整复杂了，二者就差三分之一档。

Most old cameras had a continuously variable aperture scale, with each full stop marked. Click-stopped aperture came into common use in the 1960s; the aperture scale usually had a click stop at every whole and half stop.

On modern cameras, especially when aperture is set on the camera body, f-number is often divided more finely than steps of one stop. Steps of one-third stop (1/3 EV) are the most common, since this matches the ISO system of film speeds. Half-stop steps are used on some cameras. Usually the full stops are marked, and the intermediate positions are clicked. As an example, the aperture that is one-third stop smaller than f/2.8 is f/3.2, two-thirds smaller is f/3.5, and one whole stop smaller is f/4。。。。


Typical one-third-stop f-number scale
AV -1 -0.7 -0.3 0 0.3 0.7 1 。。。。。。。。。
N 0.7 0.8 0.9 1.0 1.1 1.2 1.4 。【粗体是整档，红的是比较对象】。。。。。。。。。。
[/b]
...

深攻鲍 发表于 2018-11-12 14:35

是啊，你算错了啊，列方程应该是1/1.2^2=(1/1.4^2)*n，推出n约等于1.36啊
再补充一点，理论上通光量F1.2是F1.4的1.36倍，如果要算光圈F1.2比F1.4大几档就还要用个log2(1.36)，计算出来是这个值0.445，所以这是两个概念。

巴扎嘿嘿嘿嘿嘿 发表于 2018-11-12 14:33

可能我表述有问题
我这里指的一档 是翻译的 stop 计算的就是 T-stop
f/1.0 f/1.4 f/2.0.........  这些实际都可以看成一个 T-stop  而实际上这些数字确实不是准确值，具体应该是：
f/1.0 f/1.414  f/2.0 f/2.828.... 也就是按照 根号2的比例关系递增的

如果我没理解错的话 一个 T-STOP 理论上刚好是一倍的进光量
而我计算的则是 f/1.2 和 f/1.4理论上到底差多少个stop的进光量

巴扎嘿嘿嘿嘿嘿 发表于 2018-11-12 14:18

我算的是 T-stop  不知道官方有没有这个说法  至于我说的通光量 我实际想表达的是 理论通光量 不是实际通光量