"Yamachō, does this mean that I've succeeded? You have to keep your promise to me! "
Mo Lingwei became excited when she heard Li Zexuan's affirmation.
Li Zexuan chuckled. "Haha, you're still far from success! Back then, I asked you to build an astronomical telescope. Miss Mo, don't tell me you think you can see the moon in the sky with this little thing? "
Mo Lingwei blinked curiously. "Why can't I? My Clairvoyance can already see very far. Can't I use it to see the moon? "
"Of course not!"
Seeing that Yan Shaoning was also puzzled, Li Zexuan had no choice but to patiently explain to them, "I've told you guys before that the magnification of the Clairvoyance is related to the focal length of the objective lens and the eyepiece. The Clairvoyance that you guys are making now has a magnification of at most seven to eight times. That is to say, a person who uses this to see a distance of a thousand feet will only be able to see a distance of about ten to twelve feet. The moon is about eight hundred and eighty thousand miles away from us. Do you think we can clearly see what the moon looks like with this?"
(Usually, the moon is about four hundred thousand kilometers away from the earth. In the Tang Dynasty, Li Shimin's two steps (one step for each of his left and right feet) was used as the standard. It was called "Bu". It was stipulated that three hundred steps was one li, and one-fifth of one "Bu" was one chi. In the Tang Dynasty, one chi was 0.303 meters, and one li was 454 meters. The distance between the earth and the moon was about eight hundred and eighty thousand miles in the Tang Dynasty.)
"Eight hundred and eighty thousand miles? How far is that? "
The two of them were speechless. Yan Shaoning thought for a while and asked, "Xiaoxuan, according to what you said, we just need to increase the magnification of the Clairvoyance next?"
Li Zexuan rubbed his chin and replied, "Yes, but it's not just about increasing the magnification. When the magnification is too high, the final image of the Clairvoyance will be seriously distorted. You have to think of a way to reduce the distortion of the image. Otherwise, no matter how high the magnification is, it will be useless ~!"
Mo Lingwei frowned and asked, "Yamachō, what do you mean by image distortion?"
She could not be blamed for being ignorant. It was mainly because this knowledge had not been covered in the first volume of the physics textbook.
Li Zexuan organized his words and explained, "Previously, I told you about the imaging principle of the convex lens. In fact, those are the cases where the light rays are close to the central optical axis. But in fact, there is always a part of the light rays that are not close to the central optical axis. They are at the edge of the lens. Compared to the actual object, the final image of this part of the light rays has a certain deformation. I call it distortion!
For the Clairvoyance, if you wanted to obtain a higher magnification factor, the overall length of its optical path would have to be longer. At this time, a small distortion would become even bigger after such a long optical path! So in the future, when you increase the magnification of the Clairvoyance, don't neglect the image quality! According to my experience, as long as you can ensure that the magnification is above thirty times, you can basically meet the requirements of astronomical observation! "
Li Zexuan was very familiar with binoculars. When he was in high school, one of his roommates brought a pair of binoculars with the excuse of looking at the scenery opposite the dormitory. But in reality, he was only looking at the girls' dormitory. In the end, the boy's binoculars were confiscated by the head teacher who suddenly came to check on the dormitory.
When he was in university, thanks to the school's geographical location, he once spent thirty-five yuan to go in on the opening day of a certain planetarium in the capital. It could be said that he personally used an astronomical telescope. Moreover, his undergraduate and postgraduate studies involved a considerable part of the knowledge of optics. He even personally polished lenses during his internship. In the Tang Dynasty, he could be called an expert in optics! This was also why he could explain it to Mo Lingwei, Yan Shaoning, and the others so clearly and logically.
"Then Xiao Xuan, how should we solve the imaging distortion?"
To be honest, Yan Shaoning wasn't shocked at all by the endless stream of new knowledge that kept popping out of Li Zexuan's head because he was already numb to it. What was more important than being shocked was that he had to try his best to absorb the new knowledge that Li Zexuan spat out.
"This is very difficult!"
Li Zexuan shook his head with a complicated expression. To solve the imaging distortion and chromatic aberration problem of lenses, the method of cementing lenses was often used in modern times. By fixing two or more lenses with photosensitive glue and baking them with ultraviolet light, after going through two curing processes, a set of cemented lenses could be obtained.
In modern times, some of the precision optical components, such as the objective lens of a microscope, the eyepiece of a telescope, and so on, used lens sets that were cemented with photosensitive glue. If only a simple convex or concave lens was used, it would be very difficult to obtain a better imaging result.
However, in this era where basic science was extremely backward, wanting to control the imaging distortion like modern optical lens companies was tantamount to a fool's dream. Not to mention that there was no photosensitive glue, there was no way to even obtain pure ultraviolet light. In this case, how could they make a cemented lens set?
"Although it's very difficult, you can think of a way to replace a simple single lens with a lens set composed of many small lenses that are very close to each other. Also, you have to keep the overall imaging light path unchanged! This way, the results might be different! "
After pondering for a long time, Li Zexuan could only give it a shot and said in the end.
Yan Shaoning and Mo Lingwei both fell into deep thought.
.....
Clang, clang, clang, clang ~!
With the crisp sound of gongs and drums, Yanhuang Academy's training for the day was finally over. Qin Qiong (who was late because of the heavy rain in the morning), as the chief military instructor of the academy, blew the whistle decisively.
"School is over!"
The students' enthusiasm for training today was very high. There was no need to deliberately make things difficult for them, so Qin Qiong's impression of the instructors was quite good. Once school was over, he decisively let the students go to school without any hesitation!
"Oh! It's the holidays! "
"I can finally go home and sleep in!"
"Haha! I must eat a lot of meat these two days. Drunken Immortal Restaurant, this young master is coming! "
The students burst into cheers, and then Yanhuang College became a sea of joy. Cheers could be heard everywhere. The students ran back to the dormitory like a gust of wind, then rushed out of the dormitory, out of the college gate, and directly down the mountain to Chang 'an City.
.....
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