It is still the courtyard where Lao Su’s study room is located.
At this moment.
All the decorations in the courtyard have been removed and vacated.
In the entire yard, there was only an open space, a stone table and a few trees.
Xu Yun, along with Lao Su, Lao Jia, Xiao Li and seven or eight others, stood in the center of the courtyard.
And around them, there are a large number of exposed or sealed items, as well as...
A donkey.
Wait until everyone has arrived.
A trace of expectation flashed in Lao Su's eyes, he patted the box containing the goods and said to Xu Yun:
"Xiao Wang, everything you want is here."
Upon hearing this, Xu Yun opened a box and picked up a piece of crude glass.
He put the glass in front of his eyes and inspected it, nodded with satisfaction and said:
“No problem, the quality of the raw materials is very good.”
As a veteran in the DIY circle, Xu Yun has rubbed more than 300 lenses in his two lifetimes.
Judging the quality of glass by its feel is already an instinct engraved in the soul.
Then Lao Su carefully took a box from Mr. Xie Duguan, handed it to Xu Yun cautiously, and said:
"Xiao Wang, this thing is a bit dangerous, please keep it safe."
Xu Yun carefully took the box and placed it firmly on the stone table.
Seeing this, Xiao Li on the side couldn't help but asked curiously:
"Wang Lin, what's in the box?"
Xu Yun glanced at her and said directly:
"mercury."
Xiao Li blinked and subconsciously took a step back:
"Mercury, this is poison, what do you want to do with it?"
Seeing this, Xu Yun smiled softly. This poison, which was quite famous in the Song Dynasty, was an indispensable and important item for this mirror-making process.
He raised his head, glanced at the sky, and slowly exhaled:
"Of course it's to make... a paraboloid."
Mentioned before.
In the DIY field of later generations, Newtonian reflecting telescopes are basically the most common type.
Because compared with refractor telescopes, the optical system of Nitroscope is simple and easier to use.
At the same time, there is no chromatic aberration, and the convenience is higher than that of refractors.
The so-called convenience refers to the fact that there is only one reflective concave surface that actually participates in imaging.
However, no matter how convenient something is, it often becomes complicated when it is combined with optics.
For example, in later generations.
This choice of a single concave surface has always been quite topical.
Precisely.
It should be a dispute over which one should choose between a sphere and a paraboloid.
Later generations can prove through Fermat's principle that the paraboloid can perfectly satisfy the condition of equal optical path when parallel light is incident, so it can perfectly image parallel light.
But what about the other side.
The parabola has only one axis of symmetry and does not satisfy Abbe's sine condition.
Therefore, the paraboloid has obvious coma.
It cannot perfectly image parallel rays that are not incident along the axis of symmetry.
Even if the incident angle is small, the imaging quality will degrade rapidly.
Although the spherical surface has spherical aberration, it also has an incomparable advantage - it has countless axes of symmetry.
For a single ball, there is no such thing as off-axis rays.
In the telescope scene.
Although the spherical surface cannot perfectly image the star point, the imaging quality within the entire field of view can be guaranteed to be uniform.
Coupled with cost issues, many people cannot afford the price of paraboloids.
Therefore, in later generations, quite a few people chose the spherical surface to make a single convex surface.
But don't forget.
The prerequisite for this choice is...in the Hereafter.
The current timeline where Xu Yun is located is the ancient Song Dynasty.
Therefore, when rubbing spherical lenses by hand, there is one problem that cannot be avoided no matter what:
Xu Yun couldn't make a knife-edge instrument or an interferometer.
In fact, the knife-edge instrument is easy to say. If you really need to rub it with your hands, you can still make twenty or thirty simple prototypes.
But interferometers are difficult because they require lasers...
These two instruments are exactly the most critical, and even core, part of hand-rolled spherical mirrors:
Why is it said that DIY ball lenses with good craftsmanship in later generations can completely surpass machines?
The reason is because these two machines provide extremely precise inspection.
As long as you detect where there is an error, just rub it with soft asphalt stained with polishing powder a few times.
For example, Canon lenses - especially high-end L lenses, now have many hand-ground lenses.
As for the rest of the rotary clock and so on, it’s easier to say:
The water-borne ceremonial platform that Lao Su tinkered with was actually the earliest rotating ceremonial bell, which was like wearing it on the head of our ancestors...
Considering that this is a documentary... ahem, a rigorous novel.
Therefore, from the beginning, Xu Yun made a plan in advance:
Use rotating mercury to realize the paraboloid, and at the same time, hand-grind a spherical mirror that does not require too much precision to assist in the critical focal ratio of the aberration limit, which is an RC-like structure. (I hinted at it when using the mercury thermometer, but no one noticed it. I was disappointed.
ah.....)
Actually.
The idea of applying liquids to optical devices can be traced back to the days of Mavericks...or rather, Old Cows.
However, due to many engineering and technical difficulties, it was not until the 19th century that later generations attempted to develop reflective liquid components.
The so-called reflective liquid parabolic mirror refers to a liquid mirror made of high reflectivity mercury as the lens material.
By placing it in a stable container rotating at a constant speed of 8.5 rpm, a paraboloid can be formed.
Since there is no need for pouring, grinding and polishing of glass lenses, its cost has always been very low.
The most famous local example in later generations is the LZT Large Telescope at the University of British Columbia:
It has a super large liquid lens with a diameter of 6m, which is currently the largest liquid lens in the world.
In his previous life, when Xu Yun had not gone to sea to code, he had also participated in the design of a domestic liquid parabolic mirror, which was a national second-class project at the time.
This chapter is not over yet, please click on the next page to continue reading! A lens with a diameter of several meters costs less than half a million US dollars.
But compared to a telescope.
The more famous liquid lens in later generations was probably an advertisement for a certain Mi mobile phone, and it once dominated the hot searches.
But that thing is actually a refractive liquid lens, which is quite different from the reflective type.
His gaze returned to its original position.
After preparing many objects, Xu Yun began to assign tasks:
"Sir, mercury evaporates and is poisonous. In addition, it needs to be combined with a rotary clock, so it must be supervised by professionals.
Therefore, the liquid paraboloid is left to the villain, what do you think?"
In the past few days.
The relationship between Xu Yun and Lao Su has developed to the point where they are both teachers and friends. It has long been no longer an ordinary master and servant.
Therefore, Xu Yun's request for instructions was mainly just a formality, and Lao Su naturally would not give random orders:
"That's what you said, Xiao Wang, what other help do you need?"
Xu Yun thought for a while, pointed at Wang Zhen and another man and said:
"All it takes is the Captain and Supervisor Zhang."
Lao Wang is an officer in the army and has also been responsible for transporting food. It goes without saying that he has experience and rigor in supervision.
As for the other instrument supervisor Zhang, he is an eighth-grade instrument supervisor from the Instrument Manufacturing Bureau.
This person's full name is Zhang Jiabao, and he is probably similar to the kind of workshop supervisor who was promoted from the front line in later generations.
Zhang Jiabao was seconded to Lao Su's house a week ago. Xu Yun had seen his skills several times and his level was quite reliable.
With the help of two supervisors, the liquid paraboloid should not make any big mistakes.
Lao Su was silent for a moment, agreed to Xu Yun's request, turned to Wang Zhen and the others and said:
"Zhengchen, Zhang Qijian, you two go and help Xiao Wang."
Wang Zhen and Zhang Jiabao both took orders.
Then Xu Yun thought for a while and said:
"As for the secondary mirror... I'm afraid you will have to lead the team."
In this mirror-making plan, Xu Yun designed an RC-like structure for the telescope.
That is, based on the classic Cassegrain system and based on the primary aberration theory, an advanced version of the cow reflex is optimized.
Later generations such as the Keck telescope and the Gemini telescope all used this structure.
However, the secondary mirrors of these telescopes use convex mirrors that are extremely expensive to grind and inspect. Xu Yun obviously cannot achieve this level due to industrial capacity issues.
Therefore, he had no choice but to settle for a ball lens similar to the Dall-Kirkham system.
That is, a combined structure in which the mercury liquid paraboloid is the main component and the spherical mirror is the supplement.
Judging from the observation data.
The effective viewing angle designed by Xu Yun this time is about 1.3°, which is a half field of view angle of 0.65°.
As for the photosensitive element, Xu Yun uses fluorite, with a diagonal length of approximately 74mm.
In this way, when observing Jupiter, assume that the apparent diameter of Jupiter is 40 arcseconds.
Its size on the focal plane is: 40*1800/206264=0.776mm.
After magnifying with the eyepiece, at a clear vision distance of 250 mm, the size is almost 27.4mm.
Thus.
This ensures that Jupiter can see the alternating light and dark cloud belts, Saturn can see the rings, and Venus can see the profit and loss.
This level of imaging effect should be enough to meet Lao Su's needs.
That's right.
27.4mm.
See here.
Some students must have already reacted:
According to the effective field of view, it can be deduced that what Xu Yun wants to build this time is a giant cannon with a focal length of 4000mm! (See note)
4000mm focal length, what is this concept?
To put it most bluntly.
Its diameter is close to one meter, which is almost equal to the height of Pandora without its head.
As for the length...
No less than ten meters.
That is, something similar to William Herschel's reflecting telescope that defined the Milky Way.
Facing such a behemoth, even if the auxiliary mirror does not require too detailed data, it is still very troublesome to forge.
The first is the issue of the curvature of the secondary mirror. Xu Yun had no choice but to take action personally.
no way.
Spherical aberration is a third-order aberration that cannot be expressed within the scope of Gaussian optics, let alone the experienced experts who have not even had much exposure to Gaussian optics.
Xu Yun’s calculation plan is as follows:
According to the spherical aberration part of the Seidel aberration polynomial, the spherical aberration coefficient of a single thin lens can be written:
Here c1 and c2 are the curvatures of the two surfaces of the thin lens, s is the object distance, and y is the ray height.
As for Xu Yun’s secondary lens group.
Due to the thin lens assumption, the height of the rays on the two spherical lenses is the same.
This way you can approximate this height in the final result.
The object of the first spherical mirror A is located at infinity, and the object of the second spherical mirror B is the image of the first lens.
So we have Sa=∞, Sb=∫a.
Xu Yun had specially asked Lao Su to collect flint glass (see Chapter 125). By preparing allicin in an electrolytic cell, he could obtain standard glass with a refractive index n of 1.51680.
Yes.
When Xu Yun was preparing to make allicin, he had considered the step of the telescope and even further.
Then, by substituting the actual parameters into the solution, two sets of feasible solutions can be obtained.
One group is c1=0.000494801mm^-1, c2=-0.00173844mm^-1
The other group is c1=0.00107834mm^-1, c2=-0.0011155mm^-1 (the calculation should be correct, please correct me if there is any error)
That is to say.
There are two suitable glass curvatures.
Then transfer these two sets of data records and apply them to the formula close to 1.3 that Lao Jia and the others calculated earlier.
Then we can get the optimal music library template that can be determined theoretically without the need for an interferometer.
This chapter is not over yet, please click on the next page to continue reading! Then Xu Yun thought for a while and continued to say to Lao Su:
"Sir, according to our estimates, the grinding of the secondary mirror may take about a month.
Therefore, you and Master Qi may need to work harder in the coming days."
When Lao Su heard this, he laughed with some emotion:
"It's only ten months. If you can see the stars clearly, I can last for a year, not to mention a month!"
Then he turned around and bowed his hand to another little old man in his fifties and sixties:
"Master Qi, I'm afraid I'll have to help you this time."
The little old man quickly returned the gift:
"Don't dare, don't dare. If it hadn't been for the help from my benefactor, my whole family would have been turned into withered bones on the roadside, and how could they have enjoyed the blessings they have today?
I also ask my benefactor not to say too much, otherwise you will really embarrass me."
When Old Su heard this, he didn't say anything more, but patted the little old man's shoulder affectionately.
This little old man is also a master of the Weapon Making Bureau, named Siegfried. It is said that he is the craftsman with the best forging technology in the Northern Song Dynasty.
When Lao Su went to Ludong to check the accounts, he accidentally met Siegfried on the roadside who was fleeing a food shortage.
At that time, Lao Su saw that he was pitiful, so he took him with him out of good intentions.
Just like Xu Yun did before, he planned to arrange a servant's job after returning to Beijing.
However, by a coincidence, Old Su unexpectedly discovered that Siegfried was very good at work, even better than many craftsmen in the capital.
So Lao Su changed his mind and introduced him to work in the Instrument Manufacturing Bureau, where he was taken care of a lot during the period.
Later, Siegfried married and had children in Beijing, so the whole family treated Old Su as their benefactor.
Siegfried never turned down anything that Old Su needed from him and was within his ability, and he always tried his best to do it.
For example, the balance spring in Lao Su's self-priming pump was made by this person.
In addition, the capillary tube of Xu Yun's mercury thermometer was also made by this person.
Judging by Xu Yun's naked eyes.
This Master Qi's precision level is estimated to be comparable to that of the legendary eighth-level craftsmen of later generations. It is a type of humanoid self-propelled precision machine.
Of course.
In addition to manual work, grinding lenses also requires grinding equipment.
In 1671.
Huygens once built a machine tool that could process lenses. It was very easy to assemble, so Xu Yun copied it.
At that time, the power Huygens used was human power, which meant paying people to drive the equipment.
But now...
Xu Yun raised his head and looked at the people in the courtyard...
