"Shan Zhang, in this case, do I think I have succeeded~? Then you have to keep what you promised me back then!"
Hearing Li Zexuan's affirmation, Mo Lingwei suddenly became excited and said quickly.
Li Zexuan chuckled and said: "Haha, this is still far from success! What I said at the beginning was to let you build an astronomical telescope. Miss Mo, do you think you can see the moon in the sky with this little thing~?"
Mo Lingwei blinked curiously and said, "Why can't it work? My clairvoyance can already see very far. Can't I use it to see the moon~?"
"Of course not!"
Seeing that Yan Shaoning next to him also looked confused, Li Zexuan could only patiently explain to them: "I told you before that the magnification of this clairvoyance is related to the ratio of the focal length of the objective lens and the eyepiece. The magnification of the clairvoyance you are making now is The magnification is only about seven to eight times at most. In other words, using this to see a person a hundred feet away means zooming in to a distance of about ten to twelve feet, and the moon is about eighty feet away from us. Eighty thousand miles away, do you think we can see clearly what the moon looks like with this thing?"
(Usually, the distance between the moon and the earth is about 400,000 kilometers. In the Tang Dynasty, Li Shimin's double steps (one step each for the left and right feet) were used as the size standard, called "bu", and it was stipulated that three hundred steps were one mile, and one " One-fifth of a "step" is a foot. In the Tang Dynasty, the foot is now 0.303 meters, and one mile is 454 meters. When converted, the distance between the earth and the moon is almost equivalent to 880,000 miles in the Tang Dynasty)
"Eighty-eighty thousand miles? How far is that~?"
After the two of them heard this, they were speechless. Yan Shaoning thought for a while and asked: "Xiaoxuan, according to your opinion, do we only need to increase the magnification of the clairvoyance~?"
Li Zexuan thought about his chin and replied: "Yes, but it is not just a matter of increasing the magnification. When the magnification is too high, the final image produced by the clairvoyant will be severely distorted. You must find ways to reduce the imaging distortion. , otherwise it will be useless no matter how high the magnification is~!”
Mo Lingwei frowned and asked in confusion: "Chief Shan, what is imaging distortion?"
It’s not to blame for her ignorance. The main reason is that this knowledge has not been mentioned in the first volume of the physics textbook.
Li Zexuan organized some words and explained: "I have told you about the imaging principles of convex lenses before. In fact, those are situations where light is close to the central optical axis, but in fact there is always a part of the light that is not close to the central optical axis. They are at the edge of the lens. Compared with the actual object, the final image of this part of the light has undergone a certain deformation. I call it distortion!
For clairvoyance, if you want to obtain higher magnification, the length of its overall optical path will become longer. At this time, after a small distortion passes through such a long optical system, the degree of distortion will become larger. big! So when you increase the magnification of clairvoyance in the future, don’t ignore the image quality! According to my experience, as long as you can ensure a magnification of more than thirty times, you can basically meet the requirements for astronomical observation! "
Li Zexuan is very, very familiar with telescopes. When he was in high school, one of his buddies in the dormitory brought a telescope with him, saying that he could see the scenery across from the dormitory, but there were only girls' dormitories opposite. In the end, the skynet was restored, and the boy's telescope was confiscated by the head teacher who suddenly checked his bed.
When he was in college, thanks to the school's geographical location, he spent thirty-five yuan to sneak in at an open day of a planetarium in the capital. It was considered that he had personally used an astronomical telescope, and he was an undergraduate and graduate student. The majors he studied during this period involved a considerable part of optical knowledge, and he even polished lenses himself during his internship. In this era of the Tang Dynasty, he could be called an expert in optics! This is why he was able to explain things clearly to Mo Lingwei and Yan Shaoning.
"Then Xiaoxuan, how should we solve the imaging distortion~?"
To be honest, Yan Shaoning is not shocked at all by the endless stream of novel knowledge that always pops up in Li Zexuan's mind, because he has already been numbed by shock. What is more important than being shocked is that he needs to try his best to absorb Li Zexuan New knowledge revealed.
"This is difficult!"
Li Zexuan shook his head with a complex expression. To deal with the imaging distortion and chromatic aberration problems of lenses, the method of cementing lenses is often used in modern times. Two or more lenses are fixed with photosensitive glue, and then baked with ultraviolet light. After two After the curing process, a set of cemented lenses can be obtained.
Some modern precision optical components, such as microscope objectives, telescope eyepieces, etc., all use lens groups that are glued with photosensitive glue. If you only use a simple convex lens or concave lens, it will be difficult to obtain better imaging results.
However, in this era of extremely backward basic science, trying to control imaging distortion like modern optical lens companies is tantamount to wishful thinking. Not to mention that there is no photosensitive adhesive, and even pure ultraviolet light cannot be obtained. In this situation Next, how is it possible to make a cemented lens set?
"Although it is difficult, you can find a way to replace a simple single lens with a lens group composed of many closely spaced small lenses, and still keep the overall imaging light path unchanged! The results obtained in this way may be The difference~!”
After thinking for a long time, Li Zexuan finally had no choice but to treat the dead horse as a living horse doctor and said.
Yan Shaoning and Mo Lingwei were both lost in thought.
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"Clang clang clang clang~!"
With a burst of "clear" gongs and drums, today's training at Yanhuang Academy finally ended. Qin Qiong (who was late in the morning due to heavy rain and bad roads), as the academy's chief military training instructor, decisively blew the whistle.
"School is over~!"
The students were very enthusiastic about training today, and there was no need to deliberately make things difficult for others, so Qin Qiong had a very good impression of the instructors. When school is over, let the students go to school without hesitation!
"Oh~! It's a holiday~!"
"I can finally go home and sleep in~!"
"Haha~! I must eat a lot of meat in these two days, Zuixianlou, this young master is here!"
The students burst into cheers, and then Yanhuang Academy became a sea of joy, and cheers could be heard everywhere. The students ran back to the dormitory like a gust of wind, then rushed out of the dormitory, exited the academy gate, and headed directly to Chang'an City down the mountain.
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