objective focal length
The focal length of an objective lens is an important factor in an optical system. There were many methods to measure the focal length of an objective lens. The fixed-focal length collimator method had a large measurement range and high accuracy. The relative error was generally less than 1%. It was a commonly used measurement method. In a telescope, the multiplying power was equal to the focal length of the objective lens divided by the focal length of the eyepieces. In terms of aperture, the F value was the ratio of the focal length of the objective lens (f) to the perimeter of the entrance pupil (D). Different types of telescopes or instruments had different focal length values of the objective lens. For example, the focal length of an astronomical telescope was 400mm, and the focal length of the objective lens of the ZWJ - 851 Collimator was 200mm. Read more exciting novels for free
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>
Staircase camera focal length
For a relatively narrow environment such as stairs, a 2.8mm focal length camera could generally be used. Its field of view was larger and the range that could be seen was the largest. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
How big is the focal length of the monitor?
The focus of the monitor depended on a number of factors. First, he had to consider the scope of surveillance. If the monitoring range is small and the viewing angle is large, such as a family living room, small shops, etc., you can choose a surveillance camera with a smaller focal length. For example, a camera with a 3.6mm or 4mm focal length can have a viewing angle of 75°-90 °, and the effective monitoring distance can reach more than 5 meters, covering a space of 40 - 80 square meters. If the monitoring range is large, such as a space of 10m × 10m, you need to choose a surveillance camera with a larger focal length. Secondly, pay attention to the size of the scene to be monitored, the distance between the camera and the scene, and the size of the camera's imaging device (such as 1/3", 1/2", 2/3", or 1"). The appropriate focal length can be determined by the calculation method f = vD/V or f = hD/H (where f represents the focal length, f = vD/V: v represents the vertical height of the CCD-target surface, D represents the distance from the lens to the scene, and V represents the height of the observed object;f = hD/H: h represents the horizontal width of the CCD-target surface, D represents the distance from the lens to the scene, and H represents the width of the observed object). In addition, different focal lengths had different shooting effects. The larger the focal length, the farther the view, but the smaller the field of view. The smaller the focal length, the closer the view, and the larger the field of view. At the same distance, the larger the focal length, the smaller the angle of view, but the clearer the relative details. At the same focal length, the further the distance, the wider the angle of view, but the lower the degree of recognition. If one wanted to see a human face or figure clearly, the further the distance, the greater the focal length needed. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
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>
Laser engraving machine focal length
In the laser engraving machine, the focal length is the distance from the center of the lens to the focal point of the light. For example, the focal length of the 3DJQL- * 00L series laser engraving machine was 960 - 1440mm. In the laser marking equipment, after the laser was shaped by the laser, it would illuminate the focusing field lens (usually a concave lens) with a parallel beam. The concave lens would be refracted by the optical refraction to focus the parallel beam onto a focal point, forming a focal surface. The vertical distance from the center of the concave lens to the focal surface was the focal length, which was generally represented by F =. Most of the laser equipment's matching focusing field lens would have a label on it. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
How to choose the focal length of the surveillance camera
The following aspects could be considered when selecting the monitoring focal length: * * 1. Choose according to the monitoring range ** 1. * * Small monitoring range and large viewing angle **: For example, in a family living room or small shops, you can choose a surveillance camera with a smaller focal length. For example, a camera with a focal length of 3.6mm or 4mm can have a viewing angle of 75 °-90 °, an effective monitoring distance of more than 5 meters, and can cover a space of 40 - 80 square meters. 2. * * Large monitoring range (10m * 10m or more)**: You need to choose a surveillance camera with a larger focal length, but a larger focal length will reduce the monitoring angle. To achieve complete monitoring, you can consider using a cloud platform ball machine or installing multiple surveillance cameras. 3. * * Surveillance range is fixed and very far away (such as monitoring a parking lot 30 meters away)**: You need to choose a camera with a larger focal length, such as a surveillance camera with a 12mm or higher. * * 2. Choose based on the usage scenario ** 1. * * Narrow space (such as garage, storage room, etc.)**: It is recommended to choose 2.8mm focal length, and the best monitoring distance is within 3 meters. 2. * * Home or small shop environment **: It is recommended to choose 4 mm focal length, and the best monitoring distance is 3 - 5 m. 3. * * Family courtyard, balcony, doorway, etc. **: 6mm focal length is recommended. 4. * * A wide outdoor area without high requirements for details **: A camera with a 4mm focal length is more suitable. 5. * * Need to capture detailed information from a distance (such as license plate number or facial features)**: A camera with an 8mm focal length is more suitable. In addition, the field of view of the surveillance camera is determined by the width, height, and distance from the surveillance camera. Once the scene to be monitored is determined, the correct choice of the focal length of the lens is also affected by the size of the scene to be monitored, the distance between the camera and the scene, and the size of the camera imagers (such as 1/3 ", 1/2", 2/3 "or 1 "). The calculation method is: f = vD/V or f = hD/H (where, f represents the focal length. When f = vD/V, v represents the vertical height of the CCD-target surface, D represents the distance from the lens to the scene, and V represents the height of the object being observed; when f = hD/H, h represents the horizontal width of the CCD-target surface, D represents the distance from the lens to the scene, and H represents the width of the object being observed). After calculating the focal length value, if there was no corresponding focal length lens, one could choose a similar model according to the product catalog. Generally, one would choose a smaller lens than the calculated value, so that the viewing angle would be larger. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
How to measure the focal length of a laser lens
The focal length of the laser lens was measured as follows: 1. ** Experimental measurement method ** - ** Roughly measure the focal length of the concave lens (uncertainty not calculated)**: clearly image an object in the distance (such as the scenery outside the window or a lit table lamp more than 5 meters away in the room) on the image screen. Move the lens back and forth, and measure the distance between the concave lens and the image screen with a steel ruler. This distance is the focal length of the lens. The reading is accurate to millimeters. It is not estimated below 1 mm. - ** Measuring the focal length of the concave lens by the two-time imaging method (estimated reading: 1/2 mm, uncertainty not calculated)**: Place the object screen and the image screen on the optical bench, so that the distance between the object screen and the image screen is greater than 4 times the focal length of the lens. The distance between the object screen and the image screen was kept constant, and the concave lens was moved. The positions of the concave lens corresponding to the magnified image and the reduced image were recorded clearly on the image screen, and the focal length of the concave lens was calculated after multiple measurements. - ** Measuring the focal length of a concave lens by auto-alignment ** - ** Manual reading (uncertainty limit 0.1mm, estimated reading 1/2 division value (mm))**: Put the light source, object screen, concave lens, and reflective mirror on the optical bench in turn, move the concave lens until a clear image is seen on the object screen (the method to determine that it is a self-aligned image depends on the specific experimental situation), and record the position of the object screen and the concave lens; then rotate the concave lens around the support by 180°, repeat the above measurement, and finally calculate the focal length and uncertainty of the concave lens. - ** Laser ranging (uncertainty limit 0.2mm, minimum indication value 1mm, no estimation)**: Similarly, place the light source, object screen, concave lens, and reflective mirror on the optical bench in order. Move the concave lens until a clear image appears on the object screen. Record the position of the object screen and the concave lens. Then rotate the concave lens 180° around the support and measure again to calculate the focal length. 2. ** Calculating using optical principles **: For an ideal thin lens, the formula can be used according to the curvature radius and refraction index of the lens.(f = \frac{(n -1) \times R}{2}\)(where <f> is the focal length,<n> is the refraction index of the lens material, and <R> is the radius of curvature of the lens). For thick lenses, the thickness of the lens and the curvature radius of the two surfaces need to be considered.(<frac{1}{f} = (n-1) (<frac{1}{R1} -<frac{1}{R2} -<frac{(n - 1)d}{nR1R2})>)>, where <R1> and <R2> are the curvatures of the two surfaces of the lens, and <d> is the thickness of the lens.) 3. ** Determined according to the characteristics of the laser resonant cavity **: In the laser system, the focal length of the laser resonant cavity is related to the mode radius and the optical wavelength of the laser crystal. The focal length of the thermal lens can be determined by measuring the output power of the laser, but this process involves the influence of the thermal effect of the laser on the parameters. 4. ** Use optical design software **: In modern optical design, professional optical design software can be used to help calculate the focal length. These software can simulate the path of light in the lens and accurately calculate the focal length. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
How to find the focal length of laser welding
During the hand-held laser welding process, you can find the focal length by following the steps below: 1. Preparing: - The hand-held laser welding machine was usually equipped with a remote control or a hand-held controller, which had to be prepared to adjust the parameters of the laser. - He also needed to prepare tools for measuring focal length, such as a focal length ruler and a magnifying glass. At the same time, it was necessary to understand the basic principle, that is, the focal length was generated during the working process of the laser welding machine. It was affected by the distance between the lens or mirror and the welding material. If the focal length was not accurate, the welding effect would be worse, and there would be welding defects or a reduction in the welding strength. 2. Steps of adjustment: - Turn on the power supply of the hand-held laser welding machine, place the welding head above the welding material, and observe the focus of the laser beam. - Use the focal length ruler to measure the distance between the lens or mirror and the welding material, and record the measured value. - According to the measurement results of the focal length ruler, the remote control or the hand-held controller was used to adjust the parameters of the laser, including the size of the spot, the position of the spot, and the welding speed. - After adjusting the various parameters, the welding effect test was carried out to check whether the welding quality and accuracy met the requirements. If the welding effect was not ideal, the focal length needed to be adjusted again. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
How to increase the focal length of the camera lens
To increase the focal length of the camera lens, the following methods can be used: 1. Use a telephoto lens: The focal length of a telephoto lens is larger. For example, a 50mm lens is considered a standard lens, and a 200mm lens is a telephoto lens. Using a telephoto lens can zoom in on distant objects and make the picture more full. This is the most direct way to expand the focal length. 2. Use a magnifying lens: The magnifying lens can be directly installed on the lens to double or more the focal length. For example, the focal length of the camera lens was 50mm. After installing a 100mm magnifying lens, the focal length of the camera could be expanded to 100mm, and the cost of this method was relatively low. 3. Use digital zoom: Most modern digital cameras are equipped with digital zoom, which uses software algorithms to magnify images without changing the focal length of the lens. However, this method will cause the quality of the image to deteriorate because it is achieved by cropped images. It is not recommended to use it often. 4. Use post-production software: If you don't have a large focal length lens or a magnifying lens, you can use post-production software (such as PowerPoint or Lighthouse) to simulate a large focal length effect by trimming and adjusting the image. However, this requires a certain amount of skill and experience, and is often used in creative photography. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
How to know the focal length of a concave lens
The focal length of the concave lens can be determined by: 1. ** Concave lens assisted secondary imaging method **: Place a light source on the main optical axis of the concave lens, adjust the distance between the light source and the concave lens, so that the object point becomes a real image; According to the principle of virtual object imaging (an object becomes a real image through a lens, and the emitted light is refracted by the second lens before reaching the image point, then the first image can be regarded as a virtual object in the second image, and the focal length of the virtual object is negative), the focal length of the concave lens is obtained. 2. ** Plane mirror auxiliary method **: Put the point light source behind the concave lens to form an image, put a flat mirror vertical to the main optical axis behind the image, and put a small screen next to the light source; then put the concave lens between the concave lens and the image, move the concave lens back and forth, so that the light is refracted by the concave lens and shot out parallel. At this time, it forms a real image on the screen, and then calculate the focal length. 3. ** focal length stacking method **: measure the equivalent focal length of the two lenses and the focal length of the concave lens, and calculate the focal length of the concave lens through a formula (this method is suitable for thinner lenses, and the absolute value of the focal length of the concave lens is greater than the focal length of the concave lens. The formula derivation uses the knowledge of virtual object imaging). 4. ** Similar triangle method **: The sunlight (parallel light) is shot along the main axis to the concave lens. The diameter of the concave lens, the diameter of the light spot on the screen behind the concave lens, and the distance from the concave lens to the screen are measured. According to the geometric relationship, the focal length of the concave lens is calculated by using the similarity ratio. 5. **"Incident-exit" ray method **: insert two needles parallel to the main optical axis on one side of the concave lens, and also insert two needles on the other side of the concave lens, so that the images of these two needles and the first two needles are in a straight line, and then calculate the focal length by making the incident ray and the exit ray. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>