Into Unscientific Chapter 146

  Chapter 146 Donkey: &%￥#@!

   Two days later.

   It is still the courtyard where Lao Su's study is located.

   Right now.

   All the decorations in the courtyard have been removed and vacated.

  In the entire yard, only an open space, a stone table, and a few trees remained.

  Xu Yun took Lao Su, Lao Jia, Xiao Li and seven or eight people together and stood in the center of the courtyard.

   Around them, there are a large number of exposed or packaged items, and

   A donkey.

   Wait for everyone to arrive.

  A look of anticipation flashed in Old Su's eyes, he patted the box containing the goods lightly, and said to Xu Yun:

   "Xiao Wang, everything you want is here."

  Xu Yun heard this and opened a box, and picked up a piece of rough glass from it.

  He put the glass in front of his eyes and inspected it, nodded in satisfaction, and said:

   "No problem, the ingredients are of good quality."

  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 feel is already an instinct engraved into the soul.

  Later, Lao Su carefully took a box from Xie Laoduguan, handed it to Xu Yun cautiously, and instructed:

   "Xiao Wang, this thing is a little dangerous, so please hold it."

  Xu Yun took the box carefully and placed it on the stone table steadily.

  Seeing this, Xiao Li asked curiously:

   "Wang Lin, what's in the box?"

  Xu Yun took a look at her, but didn't give a damn, and said directly:

   "Mercury."

  Xiao Li blinked, and took a step back subconsciously:

   "Mercury, this is poison, what do you want to do with it?"

  Xu Yun smiled lightly when he saw this. This poison, which was quite famous in the Song Dynasty, is an indispensable and important item for this mirror-making process.

  I saw him raise his head, glance at the sky, and exhale slowly:

   "Of course it's for making a paraboloid."

   Mentioned earlier.

  In the DIY field of later generations, Newtonian reflector telescopes basically belong to the most common type.

  Because compared with the refracting telescope, the optical system of Niufan is simpler and easier to use.

  At the same time, there is no chromatic aberration in the cow reflector, and the convenience is higher than that of the refractor.

  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 things are, they often become complicated when they are combined with optics.

   For example in the hereafter.

  The choice of this single concave surface has always been quite topical.

Precisely.

   It should be a dispute over which one to choose between a sphere and a parabola.

  Later generations can prove by Fermat's principle that the paraboloid can perfectly satisfy the equal optical path condition for the incident parallel light, so it can perfectly image the parallel light.

   But on the other hand.

  A paraboloid has only one axis of symmetry, and does not satisfy Abbe's sine condition.

  So the paraboloid has obvious coma.

  It cannot perfectly image the parallel rays that are not incident along the axis of symmetry.

  Even if the angle of incidence is small, the image quality will degrade rapidly.

  Although the spherical surface has spherical aberration, it also has an unparalleled advantage—it has countless symmetry axes.

  For a single sphere, there is no such thing as an off-axis ray.

  In the scene of the telescope.

  Although the spherical surface cannot perfectly image the star point, the imaging quality in the entire field of view can be guaranteed to be uniform.

  Combined with cost issues, many people cannot afford the price of paraboloids.

   Therefore, in later generations, quite a few people chose spherical surfaces to make individual convex surfaces.

   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 figure out the knife-edge instrument and interferometer.

  In fact, it's easier to talk about the knife-edge instrument. If you really want to rub your hands together, you can still make twenty or thirty simple prototypes.

   But the interferometer is very difficult, because this thing needs a laser

  And these two instruments are precisely the crucial, even the core, part of the hand rubbing spherical mirror:

  Why do you say that DIY ball mirrors with good craftsmanship in later generations can completely surpass machines?

  The reason is because these two machines provide extremely precise detection.

   As long as there is an error detected, just rub it with soft asphalt with polishing powder a few times.

  For example, Canon lenses—especially high-end L lenses, there are still many hand-ground lenses.

  As for the rest of the rotary clock, it's okay to say:

  The water astronomical platform that Lao Su worked on is actually the earliest rotating instrument clock, which is equivalent to wearing it on the ancestor's head.

   Considering that this is a documentary. Ahem, rigorous novel.

  So at the very beginning, Xu Yun made a plan in advance:

  Use rotating mercury to realize a paraboloid, and at the same time, hand grind a spherical mirror that does not require too much precision to assist the critical focal ratio of the aberration limit, which is an RC-like structure. (It was hinted at when the mercury thermometer was used, but no one found it, so disappointed.)

   Actually.

  The idea of ​​applying liquid to optical devices can be traced back to the age of the calf or the old cow.

  However, due to many engineering and technical difficulties, it was not until the 19th century that later generations tried to develop reflective liquid components.

  The so-called reflective liquid parabolic mirror refers to the liquid mirror made of mercury with high reflectivity as the lens material.

   By placing it in a stable container rotating at a constant speed of 8.5rpm, a paraboloid can be formed.

   Since the pouring, grinding and polishing process of glass lenses is not required, its cost is also historically low.

  The most famous 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 hadn't entered the sea, he also participated in the design of a liquid parabolic mirror in China, which belonged to the second project of China at that time.

  The cost of a lens with a diameter of several meters is less than half a million dollars.

   But compared to the telescope.

  The more famous liquid lens in later generations should be an advertisement of a certain Mi mobile phone, and it once dominated the hot searches.

   But that thing is actually a refractive liquid lens, and there is still a big gap between it and the reflective type.

  The line of sight returns to the original place.

   After preparing many items, Xu Yun began to assign tasks:

   "Master, mercury is volatile and poisonous, and it needs to be combined with a rotary clock, so it must be supervised by professionals.

  So the liquid paraboloid is handed over to the villain, how do you think? "

  The past few days.

  The relationship between Xu Yun and Lao Su has developed to the point where they are both teachers and friends, and they are no longer in the nature of ordinary masters and servants.

  Therefore, Xu Yun's request for instructions was mainly for a show, and Lao Su naturally would not give orders indiscriminately:

   "So according to what you said, Xiao Wang, what other helpers do you need?"

  Xu Yun thought for a while, pointed to Wang Ting and another man and said:

   "Just the captain and Zhang Qijian."

  Old Wang is an officer in the army and has also undertaken the task of transporting food. Needless to say, he has experience in supervision and rigor.

  As for the other Zhang Qijian, he is a subordinate of the Eighth Grade Qijian from the Qiqi Bureau.

  This person's full name is Zhang Jiabao, and he is probably similar to the workshop supervisor who was promoted from the front line in later generations.

   Zhang Jiabao was seconded to Lao Su's residence a week ago to listen to him. Xu Yun has seen his skills several times, and his level is quite reliable.

  With the assistance of two supervisors, the liquid paraboloid should not make too many mistakes.

  Old Su was silent for a moment, agreed to Xu Yun's request, turned around and said to Wang and the two:

   "Zhengchen, Zhang Qijian, you two should go to Xiao Wang's subordinates to help."

  Wang Bao and Zhang Jiabao took orders together.

   Then Xu Yun thought about it, and said:

   "As for the secondary mirror, I'm afraid the master will lead the team."

  In this mirror-making plan, Xu Yun designed an RC-like structure for the telescope.

   It is an advanced version of Niufan optimized on the basis of the classic Cassegrain system and based on the primary aberration theory.

   Later generations, such as the Keck telescope and the Gemini telescope, all use this structure.

  However, the secondary mirrors of these telescopes all use convex mirrors with extremely high grinding and testing costs. Due to the problem of industrial capacity, Xu Yun obviously cannot achieve such a level.

  So he had to settle for the next best thing and chose a spherical lens similar to the Dall-Kirkham system.

   That is, the combined structure of the mercury liquid parabola as the main part and the spherical mirror as the auxiliary part.

  From the observation data.

   The effective viewing angle of Xu Yun's design this time is about 1.3°, that is, the half field of view is 0.65°.

  As for the photosensitive element Xu Yun uses fluorite, the diagonal length is about 74mm.

  In this way, when observing Jupiter, it is assumed that the apparent diameter of Jupiter is 40 arcseconds.

  Its size on the focal plane is: 40*1800/206264=0.776mm.

  After zooming in with the eyepiece, the size is almost 27.4mm at a distance of 250mm.

Thus.

   It can ensure that Jupiter can see the alternating light and dark cloud bands, Saturn can see the rings of Saturn, and Venus can see the profit and loss.

  This level of imaging effect should be enough to meet the needs of Lao Su.

   Exactly.

  27.4mm.

   See here.

  Some students must have already reacted:

  Based on the effective field of view, it can be estimated that what Xu Yun is going to do this time is a giant cannon with a focal length of 4000mm! (see note)

  4000mm focal length, what is this concept?

   To put it bluntly.

   Its diameter is close to one meter, almost equal to the height of Pandora without its head.

   As for the length.

   Not less than ten meters.

   That is something like William Herschel's reflecting telescope that defined the Milky Way.

  Facing such a huge monster, even if the auxiliary secondary mirror does not require too fine data, it is very troublesome to forge.

  First of all, there is the problem of the curvature of the secondary mirror. Xu Yun can only do it himself.

no way.

  Spherical aberration is a third-order aberration, which cannot be expressed within the scope of Gaussian optics, let alone Lao Jia who has not even had much contact with Gaussian optics.

  Xu Yun's calculation scheme is as follows:

  According to the spherical aberration part in the Seidel aberration polynomial, the spherical aberration coefficient of a single thin lens can be written as:

S=((c1-c2)ns+2(c1-1/s)-(c1-c2)n(2c1-3/s)+n(c1-1/s)(c2-3/s))+ (y(1-n)/n)

   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.

  For Xu Yun's secondary lens group.

  Due to the thin lens assumption, the ray heights on both spherical lenses are the same.

  Thus, we can go to 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 Sa=∞, Sb=∫a.

  Xu Yun specially asked Lao Su to collect flint glass (see Chapter 125). Through the electrolytic cell treatment of preparing allicin, a standard glass with a refractive index n of 1.51680 can be obtained.

Yes.

  When Xu Yun was preparing to make allicin, he considered this step of the telescope, and even further.

   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 (there should be no mistake in the calculation, please correct me if there is any mistake)

   That is to say.

  There are two kinds of suitable glass curvature.

  Then transfer these two sets of data records and put them into the formula close to 1.3 calculated by Lao Jia and the others earlier.

  The optimal music library template that can be determined theoretically without interferometer can be obtained.

   Then Xu Yun thought about it, and continued to say to Old Su:

   "Master, according to our estimate, the grinding of the secondary mirror may take about a month.

  So in the next few days, you and Master Qi may need to work harder. "

  Old Su smiled with emotion when he heard the words:

   "It's only ten months, if you can see the stars clearly, not to mention January, even a year old man can last!"

   Then he turned around and bowed his hands to another little old man in his fifties and sixties:

   "It's Master Qi, I'm afraid I will have to trouble you this time."

  The little old man hurriedly replied:

   "Don't dare, if it wasn't for the help of benefactor at the beginning, the whole family of the little old man would have already become dry bones on the side of the road. How could they have enjoyed the blessings they have today?

   Also please benefactor not to talk too much, otherwise it will really embarrass the old man. "

  Old Su didn't say anything after hearing this, but patted the little old man's shoulder kindly.

  This little old man is also a master of the Tool Making Bureau, named Siegfried, and it is said that he is currently the best forging craftsman in the Northern Song Dynasty.

  When Lao Su went to Ludong to check the accounts, he happened to meet Siegfried on the side of the road who was fleeing due to food shortage.

  At that time, Old Su saw him as pitiful, so he took him with him out of kindness.

  Just like what he did to Xu Yun at the beginning, he planned to arrange a job as a servant after returning to Beijing.

   But by a coincidence, Lao Su accidentally discovered that Siegfried had a good job, even better than many craftsmen in Beijing and China.

  So Lao Su changed his mind and introduced him to work in the Tool Manufacturing Bureau, and took care of him during the period.

  Later, Siegfried married a wife and had children in Beijing, so the whole family treated Lao Su as a benefactor.

  Everything that Lao Su needs and can do, Siegfried never refuses, and does his best.

  For example, the balance spring in the Laosu self-priming pump was built by this person.

  In addition, the capillary of Xu Yun's mercury thermometer was also made by this person.

   According to Xu Yun's naked eye judgment.

  The precision level of Master Qi is estimated to be comparable to that of the legendary eighth-level mechanic in later generations, and it belongs to the type of humanoid self-propelled precision machine.

Of course.

  Grinding lenses requires not only human hands, but also grinding equipment.

   in 1671.

  Huygens once created a machine tool that can process lenses, and the assembly difficulty is very low, so Xu Yun copied it.

  At that time, the power used by Huygens was manpower, that is, paying people to drive the equipment to run.

   But now

  Xu Yun raised his head and looked at the man in the courtyard.

   That donkey.

Note:

  Actually, it is not suitable to simply talk about the focal length of astronomical telescopes, but for ordinary readers to have an intuitive concept, it is reluctant to wait for a while. Readers majoring in optics do not need to go too deep~

   It's been 13 hours since 2 o'clock in the morning, ask for a monthly pass

   Too sleepy, go to bed now, maybe there is a typo, correct it when you get up

  (end of this chapter)

Chapter end