I Can Meet with Dead Scientists

Due to the absence of glass casting, grinding, and polishing processes, its production cost has always been very low.

The most famous example in the future would be the LZT large telescope at the University of British Columbia:

It possesses a super large 6m diameter liquid mirror, currently the largest in the world.

In his past life, before Xu Yun ventured into writing, he had participated in the design of a certain domestic liquid parabolic mirror, which at that time was considered a national-level project.

The mirror, with a diameter of several meters, cost less than fifty thousand US dollars.

However, compared to telescopes.

The more famous liquid lens in the future would actually be from a certain phone's advertisement, which once dominated trending searches.

But that device was actually a refractive liquid lens, quite different from a reflective one.

Returning the focus to the present.

After preparing various items, Xu Yun began to allocate tasks:

"Master, mercury evaporation is toxic, and since it needs to be combined with the Rotating Instrument Clock, it must be supervised by a professional.

Thus, I will take charge of the liquid parabolic surface, do you think that works?"

Over the past few days.

The relationship between Xu Yun and Old Su had developed to something akin to mentor and friend, far beyond the ordinary master-servant relationship.

Therefore, Xu Yun's request was mostly procedural, and Old Su naturally would not give arbitrary orders:

"As you suggested, Xiaowang, what other assistance do you need?"

Xu Yun thought for a moment, pointed at Wang Bing and another man, saying:

"I only need Captain and Zhang Qijian."

Old Wang was an officer in the army and had experience in grain transportation; his oversight and precision were unquestionable.

As for Zhang Qijian, he was a Junior Eighth Grade Instrument Inspector from the Artifact Bureau.

His full name was Zhang Jiabao, somewhat like those workshop supervisors elevated from the front lines in later times.

Zhang Jiabao had been temporarily assigned to the Old Su Mansion a week ago for use, and Xu Yun had seen his technical skills several times, which were quite reliable.

With the assistance of these two supervisors, the liquid parabolic surface should proceed without significant mishaps.

Old Su remained silent for a moment, agreed to Xu Yun's request, and turned to Wang Bing and Zhang Jiabao, saying:

"Zheng Chen, Zhang Qijian, you two will assist Xiaowang."

Wang Bing and Zhang Jiabao accepted the orders.

Afterward, Xu Yun thought for a moment and said:

"As for the secondary mirror... I'm afraid you, Master, will need to lead the team."

In this mirror-making plan, Xu Yun designed a telescope structure similar to the RC system.

It's an advanced Newtonian reflector optimized from the classical Cassegrain system according to primary aberration theory.

Telescopes like the Keck Observatory and the Gemini Observatory in later times use this structure.

However, these telescopes' secondary mirrors are ground and tested, with extremely high costs, something Xu Yun clearly couldn't achieve due to industrial limitations.

Thus, he had no choice but to opt for a spherical mirror similar to the Dall-Kirkham system.

A combination structure with a mercury liquid parabolic surface as the primary and a spherical mirror as the secondary.

Based on observational data.

Xu Yun designed an effective field angle of about 1.3°, which translates to a half-field angle of 0.65°.

For the photosensitive element, Xu Yun used fluorite, with a diagonal length of approximately 74mm.

Therefore, when observing Jupiter, assuming the apparent diameter of Jupiter is 40 arcseconds.

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

After being magnified by the eyepiece, it would be about 27.4mm at the 250mm distinct vision distance.

This way.

It ensures Jupiter's bright and dark cloud bands are visible, Saturn's rings can be seen, and Venus's phases observed.

This kind of imaging quality should adequately meet Old Su's needs.

Indeed.

27.4mm.

Seeing this.

Some students might already have realized:

Based on the effective field angle, Xu Yun was planning on creating a 4000mm focal length behemoth! (See note)

What concept does a 4000mm focal length entail?

To put it simply.

Its diameter is nearly one meter, roughly the height of Pandora minus the head.

As for its length...

No less than ten meters.

Similar to William Herschel's reflective telescope that defined the Milky Way Galaxy.

Faced with such a colossal entity, even if the auxiliary secondary mirror doesn't require overly precise data, its fabrication is still tremendously cumbersome.

The foremost issue is the curvature of the secondary mirror, something Xu Yun could only personally undertake.

No way.

Spherical aberration is a third-order aberration, which cannot be expressed within the scope of Gaussian optics, let alone by Old Jia, who hasn't even touched much of Gaussian optics yet.

The calculation plan from Xu Yun 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)²n³s + 2(c1-1/s)² - (c1-c2)²n²(2c1-3/s) + n(c1-1/s)(c2-3/s)) + (y³(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 height of the light ray.

As for Xu Yun's secondary mirror group.

Since the thin lens assumption is used, the height of the rays on the two spherical lenses is the same.

Therefore, this height can be canceled out in the final result.

And the object of the first spherical mirror A is at infinity, the object for the second spherical mirror B is the image of the first lens.

So Sa = ∞, Sb = ∫a.

Previously, Xu Yun specially asked Old Su to collect flint glass (see Chapter 125), which, when treated through the electrolytic cell for preparing allicin, can yield standard glass with a refractive index n of 1.51680.

Yes.

Earlier, when Xu Yun was preparing to make allicin, he was already considering this step for the telescope, and even further ahead.

By substituting the actual parameters to solve, two feasible solutions can be obtained.

One set is c1=0.000494801mm^-1, c2=-0.00173844mm^-1

The other set is c1=0.00107834mm^-1, c2=-0.0011155mm^-1 (no errors were calculated, but if there are errors, please feel free to correct them)

In other words.

There are two suitable glass curvatures.

Next, by transferring and applying these two sets of data to the formula previously calculated by Old Jia and the others that is close to 1.3.

Theoretically, the optimal template of the curve library can be determined without needing an interferometer.

Then Xu Yun thought for a while and continued to say to Old Su:

"Sir, according to our estimation, grinding the secondary mirror may take about a month.

Therefore, in the coming days, we might need you and Master Qi to work a bit harder."

Old Su, hearing this, smiled with some emotion:

"A mere month; if I can see the stars clearly, even if it's a month, a year, I can still hold on!"

Then he turned around and cupped his hands towards another small old man in his fifties or sixties:

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

The small old man quickly returned the courtesy:

"I dare not, I dare not. If it wasn't for your help back then, I'm afraid my entire family would've perished long ago. How could we enjoy today's blessings?

Please, sir, don't say more, otherwise, it truly embarrasses this old man."

Old Su stopped speaking upon hearing this, and warmly patted the small old man's shoulder.

This small old man is also a master at the Artifact Bureau, named Siegfried, who is said to be the best craftsman in forging techniques in the Northern Song dynasty right now.

Back then, when Old Su went to Lu Dong to check accounts, he happened to encounter Siegfried, who was fleeing due to a famine, by the roadside.

Old Su, seeing him pitiful, brought him along out of kindness.

Just like he did with Xu Yun, he planned to arrange a servant job for him once returning to the capital.

However, by coincidence, Old Su discovered that Siegfried possessed quite exceptional craftsmanship skills, even surpassing many artisans in the capital.

Thus, Old Su changed his mind and introduced him to work at the Artifact Bureau, taking care of him during this period.

Later, Siegfried got married and started a family in the capital, treating Old Su as a benefactor.

Whenever Old Su required something achievable by him, Siegfried never refused, always doing his utmost.

For instance, the balance spring in Old Su's self-suction pump was crafted by this person.

Also, the capillary tube of Xu Yun's mercury thermometer was made by this person.

In Xu Yun's judgment through the naked eye.

This Master Qi's level of precision is probably comparable to the legendary eighth-grade technical workers of later ages; he is a human precision machine.

Of course.

In addition to needing manpower for lens grinding, grinding equipment is also necessary.

In 1671.

Huygens once made a machine tool capable of processing lenses, which was very simple to assemble, so Xu Yun replicated it.

At that time, the power Huygens used was manpower, meaning he paid people to drive the equipment operation.

But now....

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

At that donkey.

........

Note:

In reality, it's not too suitable to simply discuss focal lengths concerning astronomical telescopes, but for the sake of providing an intuitive concept for general readers, a rough equivalency was made; optics professionals need not delve too deeply into this~