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光影如何转换为照片?

How Does a Photon Become a Film Photo?

[音乐]
[♪ INTRO]
我们拍照的大多数时候
For most of the time we’ve had photography,
都不可能直接从手机上得到一张照片
you couldn’t just snap a picture on your phone.
必须使用特殊制备地胶片才行
You had to use specially made film.
拍出一张完美的照片意味着你必须通晓一些化学知识
And taking the perfect photograph meant you had to master some chemistry,
从捕捉光线到生成肉眼可见的图片
from capturing light, to developing an image that you can see.
当光子进入胶卷相机时 其能量也穿过镜头
When photons enter a film camera, these packets of light energy fly through the lens and hit
撞击在覆盖有乳液的塑料片上
a piece of plastic covered in what’s called an emulsion.
对化学家来说 这可能是一个稍有误导性的名字
And for you chemists out there, that might be kind of a misleading name.
在化学中 乳液指两种或多种不互溶液体的混合
In chemistry, an emulsion is a mixture of two or more liquids that normally can’t
就像美味的调味汁里的油和醋
be combined, like the oils and vinegar in a tasty vinaigrette.
严格来说 涂在胶卷上的物质更接近于
The stuff coating a film strip is technically closer to a suspension,
漂浮着许多微小固体颗粒的悬浮液
which has tiny solid bits floating around in a fluid.
有代表性地 是悬浮在胶状体中的卤化银晶体
Typically, it’s silver halide crystals floating around in gelatin,
其最终固定在胶卷上
which solidifies on the film.
卤化银由银原子与卤素原子组成
Silver halides are just atoms of silver bound to atoms of any element known as a halogen,
卤素原子包括像溴 氯 碘等元素
which includes things like bromine, chlorine, and iodine.
卤化物还被叫做盐
Another name for a halide is a salt.
例如 普通食盐是由钠和氯组成的卤化物
Like, ordinary table salt is a halide made from sodium and chlorine.
卤素能与金属反应生成卤化物晶体
Halogens can react with metals to form halide crystals,
晶体中原子以非常有序的格子排列 称为晶格
in which the atoms become arranged in a very orderly grid called a lattice.
其中所有原子都被电离:它们要么失去一个电子
And all those atoms are ionized: they either lose an electron
要么得到一个电子 从而得到一个电荷
or gain one to give them a charge.
直到被光线照射到
Until they’re struck by light.
例如 光子撞击胶卷表面的溴化银晶体时
When a photon hits a crystal of silver bromide on a film strip, for instance, it knocks an
从带负电的溴离子上“敲掉”一个电子 生成一个溴原子
electron off a negatively-charged bromide ion to create an atom of bromine.
接着 该电子在晶格中移动 直到融入晶格缺陷中
Then, that electron moves around the crystal lattice until it settles into a defect.
最终它与附近的一个银离子结合
And eventually it can combine with a nearby silver ion
使其转化为带中性电的银原子
to turn it into a neutrally-charged silver atom.
随着更多的光照射在乳液上 这个过程反复进行
As more light hits the emulsion, this happens over and over again,
并且生成更多的金属银
and creates small pockets of metallic silver.
但仍有很多的溴化银存在
There’s still plenty of silver bromide left over, though.
光子不会改变所有的卤化物
The photons don’t change every halide.
为了使胶卷被适当的曝光 只有部分银原子需要被改变
Only some of the silver atoms need to be changed in order for the film to be considered exposed.
但此时你还不能在胶卷上看到任何图案
You still can’t see anything on the film at this point, though.
为了使图案清晰地显示出来 胶卷需要
In order to make that image appear clearly, the film needs to be developed
通过其他的化学反应进行显影
With another chemical reaction!
化学显影剂取决于所用胶卷的种类
Chemical developers vary depending on the kind of film you’re using.
但基本思路都是与残留的卤化银晶体反应
But the basic idea is that they react with the remaining silver halide crystals
生成可见的图案
to create an image you can see.
重点是 显影剂里包含还原剂
The important thing is that developers include reducing agents: chemicals that generally
它能在化学反应中给其他化合物提供电子
donate electrons to other compounds during a chemical reaction.
此反应中 电子受体是残存的银离子
In this case, the recipients of those electrons are the remaining silver ions.
曝光的卤化物晶体含有金属银 该晶体的银离子
The silver ions in the exposed halide crystals, the ones with metallic silver in them,
与显影剂反应更加充分 从而生成更多的金属银
will have more reactions with the developer, creating more metallic silver in those grains.
现在 你或许会想 金属银会不会像
Now, you might assume that the metallic silver will look like
昂贵的餐具里闪亮的勺子
shiny spoons in a fancy dining set.
但为形成镜状表面 银原子必须严格按照统一模式排列
But in order to have that mirror-like surface, the silver atoms have to be arranged in a
所以它们能向相同的方向反射光线
rigid, uniform pattern so they all reflect light the same way.
但当你近距离观察一张照片
When you look closely at a photograph, though,
你会发现 胶卷颗粒是不平整的
you can see that the film grains are bumpy and uneven.
在胶卷上 金属银其实看起来是黑色的
On a piece of film, metallic silver actually looks dark.
更多光子撞击卤化银晶体 会引发更多显影剂反应
If more photons hit a silver halide crystal, more reactions with the developer can happen,
并且胶卷上的该点也会变得更暗
and that spot on the film strip becomes darker.
一般来说 拍照时
Now, generally, when you take a picture,
影像会有亮区和暗区
your image will have brighter areas and darker areas.
与来自树影下的光线相比 天空会有
There’s more light coming from the sky into your camera lens
更多的光线进入你的镜头
than from a shadow under a tree.
更多的光线照射到胶卷
And the more light that hits the film,
化学处理后产生更多的金属银
the more metallic silver you get after it’s developed.
所以图像的这一部分会更暗
So that part of the image will look darker.
基本上 暗区看起来亮些 亮区看起来暗些
Basically, shadows will look bright, and highlights will look dark.
(这是)因为 明和暗的信息被颠倒了
Because the light and dark information has been reversed.
我们称其为负片
We call this a negative image.
摄影师用负片制作相片的副本
Photographers use negatives to make copies of their pictures.
他们透过负片把光照到另一张像纸上
They shine light through the negative onto another piece of photographic paper,
使得曝光反应再次进行
to make the exposure reaction happen again.
但这次 负片中暗的部分阻挡光照到副本上
But this time, the dark parts of the negative block light from reaching the copy.
所以当副本显影时 现实中明亮的部分
So when the copy is developed, the areas where the highlights were in real life
打印出来时也会更亮
show up brighter on the print.
暗区同理
And vice versa with the shadows.
这张新照片就是正片 正如你开始见到的那样
This new photo is a positive image, like what you originally saw!
如果你有胶卷相机 可以试一试
So if you get your hands on a film camera, give it a shot.
不像手机拍的自拍照 它需要一点化学知识
It’s not the same as taking a selfie with your phone, but with a little chemistry knowledge,
胶卷一点也不难懂
film isn’t so mysterious after all.
感谢观看这一集的SciShow
Thanks for watching this episode of SciShow,
特别感谢在Patreon上赞助我们的观众
and a special thank you to all our patrons on Patreon.
如果你想支持更多相关视频
If you want to help support more videos like this one,
可以到Patreon.com/SciShow
you can go to Patreon.com/SciShow.
最后别忘记到YouTube.com/SciShow订阅我们
And don’t forget to go to YouTube.com/SciShow and subscribe!
[音乐]
[♪ OUTRO]

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视频概述

胶卷、照片,曾经记录下我们无数美好回忆。可你知道它的工作原理吗?本视频带你了解胶卷中的化学知识,感受光影的魅力。

听录译者

收集自网络

翻译译者

leoma

审核员

审核团V

视频来源

https://www.youtube.com/watch?v=gIicTlGaGQE

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