to count the exact number of horsemen 5 leagues away, and on top of that can tell that their

能數五里格外騎兵的精確數量， 他更說騎兵的領袖

leader is very tall. But even with the most perfect eyes possible, would anyone be able

很高大。但是就算有最好的眼睛， 有沒有人可以

to see that far?

看到這麼遠？

When we see, we're looking at light that's traveled outwards from a light source, bounced

當我們看東西，我們看到的是 光從光源走出來，在

off an object, passed through the lens in the eye, and been focused into an image on

在物件上反彈，經過眼睛的 晶狀體，然後影像在

the retina. Except... light isn't a particle traveling in perfectly straight lines - it

視網膜對焦。但是... 光不是一粒 在直線上移動的粒子 - 光

is a wave. And therein lies the problem, both for us, and for Legolas.

是波形的，這就是問題所在，對我們 和勒苟拉斯都一樣。

Because any wave - whether water, sound or light - that travels through a small opening

因為所有波浪都一樣 - 無論是 水，聲音，還是光 - 當經過一個小孔，

will become spread out by a process known as diffraction, which for light, essentially

就會散開，這個現象叫 繞射，當光繞射，

blurs the image.

就會模糊影像。

You can see this with a telephoto camera lens where the camera aperture has been made very

你可以看到這個相機鏡頭 的光圈調節到很小

very small - small details in the photograph start to become spread out, blurred, and even

照片中微小的細節開始 變得模糊，甚至

indistinguishable! Or, if you hold the edge of a piece of paper in front of your eye and

不能辨別。或者，你把一 張紙的角放你眼睛前面，

try to read past it, small words will become blurry!

嘗試閱讀一些文字， 微小的字會變得模糊！

The blur that a small point of light spreads out to become is called an Airy disk, and

穿過一個孔然後散開 的光叫艾里斑，

the size of the Airy disk for distant tiny objects depends only on the wavelength of

微小物體的艾里斑，大小 是根據光的波長

light in question and the size of the opening you're looking through. So for visible sunlight

和它經過的孔的大小，所以， 如果是可見光和

and a human-sized pupil, diffraction limits us to at best be able to distinguish objects

跟人一樣大小的瞳孔，繞射 限制我們只能辨別大過

that are bigger than seven one-thousandths of a degree, for example, an object one centimeter

7千分之一度的東西， 例如一個1厘米大

in size a hundred meters away,. Another way of putting this is that everything 100m away

和一百米的物體，就是 指一百米外和

and smaller than 1cm gets blurred so that it appears to be about 1cm in size, no matter

小過一厘米的東西模糊 得像一厘米大，無論

how small it really is - subtle details smaller than 1cm blur away.

那件東西是多麼小 - 小過一厘米 的細節就會變得模糊。

So when Legolas, who has very human-sized pupils, looked at the riders of Rohan 24 km

當一位有跟人類相似的眼睛的 勒苟拉斯看到24公里外的洛汗騎兵，

away, diffraction tells us that everything smaller than 3 METERS would have been blurred

繞射會使所有小過3米 的東西變得模糊像

to about three meters in size - perhaps he could still count the number of horsemen,

大約3米大 - 他可能可以 點算出騎兵的數量，

but he definitely couldn't distinguish their heights to within a few centimeters...

但他一定不可能分別出 他們相差幾厘米的高度...

Unless Legolas could see in ultraviolet. Shorter wavelength light diffracts less, so if he

除非勒苟拉斯可以看到紫外光，波長較短的 光繞射情況較少，所以如果

could see in the extreme UV, then he'd be able to distinguish objects 10 cm in size,

他能看到極端紫外光，他就 能分辨出10厘米的差別，

almost enough to discern the height of a man.

差不多足夠出辨別人的高度。

Except that pretty much any kind of air absorbs extreme UV light - so even if he could see

可是空氣裡面大部分的氣體吸收 極端紫外光 - 即使他能夠看到

UV, Legolas would have been left in the dark. Or maybe it's just... magic.

紫外光，勒苟拉斯就會困在黑暗裡。 或者，他可能... 擁有魔法。