Excuse me, how do I calculate the focal length of my glasses?
The focal length of the glasses was calculated according to the relationship between the focal power and the focal length. First of all, it was clear that the focal length was "D = 1/f"("f" is the focal length, the unit is meters, and "1/m" is also called refraction), and the power of the glasses was the focal length multiplied by "100". If you know the power of the glasses, you can first divide the power by <<100>> to get the focal length, and then calculate the focal length according to the focal length formula, which is <
How to calculate the focal length of glasses
The power of the glasses was multiplied by the focal power by 100 (focal power refers to the inverse of the focal length, and the unit of focal length is meters), that is, the power = 1/f × 100. From this, the focal length f = 100/degrees (meters) could be derived. For example, a pair of 400-degree glasses would have a focal power of <i>= 400/100 = 4, and a focal length of f = 1/4 = 0.25m = 25cm. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
Normal focal length of glasses
Normal glasses included short-sighted glasses and far-sighted glasses (presbyopic glasses). The focal length was related to the degree of the glasses. For short-sighted glasses, the degree and focal length were in an inverse relationship, that is, the shorter the focal length, the higher the degree. For long-sighted glasses (presbyopic glasses), the degree of the concave lens (far-sighted lens) was positive, and there was a similar relationship between the degree and focal length. To be specific, the power of the lens was equal to 100 divided by the focal length (in meters). For example, a 100-degree spectacles would have a focal length of 1 meter. However, it was not clear whether "normal glasses" were short-sighted or farsighted, so it was impossible to determine a specific focal length value. This was because different degrees of glasses had different focal lengths. From correcting mild vision problems to high vision problems, the focal length would vary greatly. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
Distance and the focal length of glasses
The relationship between the distance and the power of the glasses was: the power of the glasses = 10000/distance (in centimeters). As for glasses for short-sightedness, the focal length corresponding to the degree was related to the distance of the far point. The degree of short-sightedness could be seen as a concave lens of the same degree in the eye. The far point was the focal length of the concave lens, and the focal length of the concave lens was the inverse of the focal length, that is, focal length x focal length = 1. For example, if you have 50 degrees of nearsightedness, the focal length can be calculated to be 2 meters according to the relationship between focal power and focal length. This is also the distance of the far point when you have 50 degrees of nearsightedness. The distance between the far point of the myope and the front of the eyeball is equal to the focal length of the concave lens needed to correct the myope. For example, the far point of-2.0D myope is 50cm in front of the eye, and the far point of-4.0D is 25cm in front of the eye. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
Wearing glasses, focal length changes
Under normal circumstances, glasses were mainly worn to correct vision so that light could be focused on the retina. For nearsighted people, the concave lens they wore would diverge the light, causing the image that was originally in front of the retina to move back to the retina. For farsighted people, the concave lens would converge the light, causing the image to move from the back of the retina to the retina. When wearing glasses, the optical system formed by the eyes and glasses changed the path of light transmission, thus affecting the focal length. For example, the higher the degree of the glasses, the shorter the focal length, and the stronger the ability to disperse light, so that the eyes can focus and form images in a relatively short distance; the higher the degree of the glasses, the shorter the focal length, and the stronger the ability to converge light, helping the eyes to focus in a normal distance. If you take off your glasses with one hand, it is easy to distort the glasses. This distortion may affect the focal length of the glasses and damage your vision. When looking at nearby objects (such as mobile phones), if a nearsighted person wears glasses, the ciliary muscles need to adjust the focal length again. If he wears glasses to look at nearby objects for a long time, the overwork of the ciliary muscles may lead to an increase in nearsightedness. In addition, different degrees of glasses correspond to different focal lengths. The calculation method is that the degree is 100 times the inverse of the focal length (for concave lenses, the degree is negative, and for concave lenses, the degree is positive). For example, glasses with 400 degrees of nearsightedness (-4.00D) have a focal length of 0.25 meters. In short, the wearing of glasses was closely related to the change in focal length, and the accuracy of focal length directly affected the health of vision. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
intelligent focal length presbyopic glasses
Smart focus presbyopic glasses did not have a focal length that could be changed automatically. Instead, there were multiple focal lengths on a pair of glasses. The lenses were distributed with different focal lengths from top to bottom, so the degrees of different positions of the lenses were different. There were many degrees, such as 50 - 250 degrees auto-focusing, and 100 - 700 degrees auto-adjusting. Some smart zooming presbyopic glasses had anti-blue light functions, and the price was different. There were 2.99 yuan and 29.9 yuan for two pairs. This kind of glasses could better assist the eyes in adjusting the focal length to solve the problem of short-distance vision caused by the weakening of the elasticity of the crystalline lens due to age, so that the wearer could obtain a clearer visual effect. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
How to calculate the focal length of a telephoto lens
If it was a digital camera, the zoom ratio was the ratio between the longest focal length and the shortest focal length of the lens. For example, if the actual focal length of a camera was a-bmm, the zoom ratio would be b/a. However, because the size of the sensor in a digital camera was different from the size of a 135 film, there was a factor conversion problem. This factor was the ratio of the size of the sensor in a digital camera to the size of a 135 film. The actual focal length of a digital camera multiplied by this factor was equivalent to the focal length of a 135 film camera. The size of the sensor in a full-frame digital camera was the same as that of a 135 film, so there was no problem with the focal length conversion factor. The telephoto distance of a phone was calculated by the zooming ratio. For example, a 5x zoom was equivalent to 120 for a 35mm film focal length, and 10x was equivalent to 240. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
How to calculate the focal length of a camera lens
The focal length of the lens was calculated based on the size of the field of view, the distance from the lens to the object being captured, and the size of the image. The specific calculations were as follows: 1. ** Calculating the relationship between the focal length of the lens and the field of view, object distance, and image size ** - When the width of the image (the width of the image of the object on the CCTV target), the width of the object, and the distance from the object to the lens are known, the focal length of the lens is (f = wL/W); - When the height of the image (the height of the object on the LCD target), the height of the object, and the distance from the object to the lens are known, the focal length of the lens is (f = hL/H). 2. ** Field of view calculation ** - If you know the horizontal field of view, or the vertical field of view, you can calculate the width of the scene according to the formula. - Horizontal field of view <<beta>= 2tg^{-1}<frac{w}{2f}>>, vertical field of view <<q>= 2tg^{-1}<frac{h}{2f}>>(Here,<w>>,<h>>,<f>> are image width, image height, and lens focal length respectively). In addition, the concept of equivalent focal length (equivalent focal length = focal length x equivalent coefficient) was also involved when matching lenses with different frame cameras, which helped to compare the imaging effects of lenses between different frames. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
Knowing the lens size, how to calculate the focal length
If it is a thin lens, the focal length can be calculated according to the object-image distance formula of the thin lens. The focal length depends on the lens 'geometry (the curvature radius of the two surfaces) and the material (the material's refraction index), but also the refraction index of the medium on both sides. When it is used in air (the refraction index of the medium on both sides is approximately 1), the focal length can be calculated according to the lens manufacturer's formula. If it is a non-thin lens, the thickness of the lens must be considered when calculating the focal length. The focal length formula is different from that of a thin lens. The specific formula is [specific formula]. At the same time, according to the focal point of the lens, a lens with a real focal point (f 'and f> 0) is called a positive lens or a converging lens; a lens with a virtual focal point (f' and f <0) is called a negative lens or a diffusing lens. When the refraction index of the lens material is greater than the refraction index of the medium on both sides, a concave lens is a positive lens, and a concave lens is a negative lens. In addition, the focal length of the concave lens was related to the radius of curvature. The larger the radius of curvature, the larger the focal length, and the smaller the amplification factor. The smaller the radius of curvature, the smaller the focal length, and the larger the amplification factor. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
The principle of measuring the focal length of glasses with sunlight
According to optical principles, for a concave lens, parallel rays (such as sunlight can be regarded as parallel rays) will converge at a point after passing through the concave lens. The distance from this point to the center of the lens is the focal length. Mythic spectacles were concave lenses, and the focal length of concave lenses could be obtained indirectly by using the relationship between concave lenses and concave lenses. When a beam of parallel sunlight passes through the concave lens, it will converge into a focal point. Put the glasses (concave lens) in front of the concave lens. Because the concave lens has a dispersing effect on the light, it will make the light that was originally converged by the concave lens diverge again. At this time, the light screen needs to move back a certain distance to get a clear image point again. By measuring the distance change before and after this movement and the known focal length of the concave lens, etc. The focal length of the concave lens (spectacles) could be calculated using optical imaging formulas. However, this process involved more complicated optical imaging principles and formula calculations. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
How does the focal length of the camera lens calculate the distance?
1. First, it was the calculation of the focal length of the lens, the size of the field of view, and the distance between the lens and the object being captured: - There are formulas,[f = wL/W] and [f = hL/h]([f] is the focal length of the lens;[w] is the width of the image, which is the width of the image of the object on the target surface of the camera;[W] is the width of the object;[L] is the distance from the object to the lens;[h] is the height of the image, which is the height of the object on the target surface of the camera;[H] is the height of the object.) - The installation distance or the field of view can also be calculated according to the angle of view, the distance between the camera and the object, or the width of the object to be seen, with the formula, Tan(alpha/2)=0.5×V/D. 2. In addition, if you know the horizontal or vertical field of view, you can calculate the width and height of the scene according to the formula.(\beta = 2tg^{-1}\)(Part of the formula content is omitted here, related to <w>,<H>,<F>), vertical field of view <(q = 2tg^{-1})(also omitting part of the formula content, related to <w>,<H>,<F>). There is a certain relationship between the horizontal field of view and the vertical field of view (<q=> or <q =>). Combined with the relevant known quantities (such as the size of the object, the field of view, etc.), using the above formula relationship, you can calculate the distance-related quantity under the condition that the focal length of the lens is known. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>