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隐形现身:超慢镜头下看纹影法成像过程 – 译学馆
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隐形现身:超慢镜头下看纹影法成像过程

Seeing the Invisible: Schlieren Imaging in SLOW MOTION

如果有一个大门 通过它你可以看到所有隐形的
If there were a portal through which you could see all of the invisible
气流 温度梯度 压力差以及
air currents, temperature gradients and differences in pressure and
空气成分
composition of air,
那么这就像是划火柴
then this is what it would look like to strike a match.
这是从气球中挤出的氦气
This is helium being squeezed out of a balloon.
你可以看到温暖的空气从你的手上升起
You could see the warm air rising off your hands.
看到异丙醇上空的无形气体 当你打喷嚏时可以看到羽毛状的物质喷射出来
The invisible vapors of isopropyl alcohol and a plume of ejected material when you sneeze.
这就是拍摄以上视频的装备
This is the setup for how I made those shots over here
我有一个直径为40厘米的凹面抛物面反射镜
I have a 40 centimeter diameter concave parabolic mirror
通常这种反射镜是用来制作望远镜
normally this would be used to make a telescope
一旦反射形成 只是一个巨大球形的一小块
but if it’s formed, just a tiny piece of a big spherical shell
对吗 一个巨大的球形镜子 我们在里面
Right? A giant spherical mirror that we’re inside
那么镜子的中心就在这里
then the center of that mirror would be right here
我把LED放在这里 它直径只有3毫米
And that’s where I’ve placed this led it’s three millimeter
但是我试着用一些黑色指甲油使光源变得更小
But I try to make the light source even smaller by painting it with some black nail polish
所以我们试着去接近一点那光源现在那光
so, we try to approximate a point source of light there now that light
向四面八方扩散 光照在镜子上发生反弹并反射回来
spreads out in all directions, and it bounces off the mirror and reflects back
几乎接近于光源
Almost to exactly the point where the light is
你可以看到光会聚在一个点上
you can see that the light converges to a point right there
现在我把光线稍微偏移了一点 这样光线就可以
Now I’ve offset the light just a little bit so that this light
直接穿过镜头进入我的镜头
will pass straight through and into the lens of my camera
因此我把刀片放到这个位置
So right here, I position this razor blade,
这样它阻挡了一半的光线通过
so it cuts off about half the light passing through
此设置能让你看到镜子前面的细微变化
This setup allows you to see tiny variations in what is in front of the mirror
例如当你的蜡烛冒出热气时
For example when you have hot gases coming off of a candle
你可以看到 因为LED的反射光
Well, you can see that because as the reflected light from the led
穿过这股热空气时
Passes through this column of hot air
它会轻微的改变方向 那就是折射
It changes directions ever so slightly that is it refracts
其原因在于在它热空气的折射率
and the reason for that is because the refractive index of hot air
不同于周围较冷空气的折射率
is different from the refractive index of the cooler air around it
现在折射率是测量光在介质中传播的速度的一种量度
Now refractive index is a measure of how fast light travels through a medium
相对于真空中的速度
Relative to its speed in a vacuum
对于空气来说 这个数值相当接近1 但更热的空气实际上折射率较低
So for air the value is pretty close to 1 but hotter air actually has a lower index of refraction
在这种情况下 折射率的差别非常微小
in this case the difference in refractive index is incredibly tiny
所以我们没有注意到光的偏转
and so we don’t notice the deflection of the light
但是有了这个设备
but with this setup
它实际上会产生不同 因为一些光会通过这个刀片
It actually makes a difference because some of the light that would have passed over this razor blade
取而代之的是光线向下偏转并被阻止并在图像上形成一个较暗的点
Instead gets deflected down and gets blocked and that forms a darker spot on the image
类似地 一些射中刀片的光线会被偏转
Similarly some light that would have hit the razor blade is instead deflected over
它在图像上创造了一个亮点 那就
it creating a brighter spot on the image and that
是如何运作的 所以你可以看到热量从你的头上升起
is how this works, so you can see the heat rising off your head and
你可以看到你的呼吸
You can see your breath
你可以看到冰冷的空气从一杯冰中涌出
And you can see the cold air poured out of [a] cup of ice
但温度并不是影响折射率的唯一因素
But temperature is not the only thing that affects the refractive index
不同材料不同物质
different materials [different] substances
它们有不同的折射率 例如打火机中的丁烷 显然我们用肉眼看不见
They have different refractive indices for example the butane in a lighter obviously we can’t see that
现在就能拍到它出来了 但相机甚至可以在打火机点燃之前就能拍到丁烷
It’s coming out right now, but the camera can even before the lighter is lit
当它通过气泡时 光也会折射
light also refracts when it passes through a bubble
折射的角度取决于气泡膜的厚度
and the amount depends on the thickness of that bubble film
这种技术被成为纹影摄影 基于德语单词[ FLIR ]命名
This technique is known as Schlieren based on the German word [flir]
意思是条纹 第一次发现纹影摄像是在
which means streak and it was first observed in
1665年 罗伯特·胡克曾用
1665 by Robert Hooke who was using
两支蜡烛和一些透镜 在19世纪
Two candles and some lenses then in the 19th century
他们用这种方法试图找出缺陷和制作镜头的玻璃
they used this method to try to find defects and the glass used to make lenses
且人们最近已经使用纹影摄影进行研究
and more recently people have used Schlieren to study
空气动力学和流体流动 因为它可以让你看到温度梯度中的压力差
Aerodynamics and fluid flow because it allows you to see those pressure differences in temperature gradients
那么 你可以看看冲击波和气体成分的差异
So [you] can look at [shockwaves] and differences in the composition of gases
所以当你观看火柴发出的光时 你正好能看到摩擦产生的热量
So when you watch the lighting of this match you’re seeing heat generated from Friction
点燃磷 从而产生更多的热量
Igniting phosphorus which in turn generates more heat
开始硫和氯酸钾之间的反应
and begins the reaction between sulfur and potassium Chlorate
开始释放二氧化硫 你也可以看到
which releases sulfur dioxide which you can also see
当我吹灭火焰时 你可以看到我的呼吸
And you can see my breath as I blow [out] the flame [I]
我非常兴奋 我能把这装置搭建起来
Am so excited that I got this set up to work
那么如果你能想到任何在暗影照相中看起来很酷的东西 请在评论中告诉我
So if you can think [of] anything that would look really cool in Schlieren, then let me know in the comments
我会试着让它产生 如果你是这个频道的新观众 我们点击这里订阅
And I will try [to] make [it] happen, and if you’re new to this channel, [we’ll] click here to subscribe
我有一些很棒的视频很快就要来了
I’ve got some awesome videos coming up very soon

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视频概述

一个通过技术手段与摄像器材来记录光与空气的微妙变化的视频。

听录译者

收集自网络

翻译译者

ID034118

审核员

审核团C

视频来源

https://www.youtube.com/watch?v=4tgOyU34D44

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