90 focal length lens group photo
When taking group photos, a 90mm focal length lens was a more suitable choice. The standard lens had many advantages when taking group photos, such as the smallest distortion and the closest to the human eye's visual perception. When using a 120 medium format 6×7 camera to take a group photo of more than 500 people, using a 90mm lens could achieve better results. However, when using this focal length lens to take a group photo, one also had to consider other factors such as shooting distance, aperture, shooting time, queue position, etc., in order to take the ideal group photo. For example, it is recommended to choose soft natural light when shooting, such as 9 - 10 a.m. or 4 - 5 p.m.(It needs to be adjusted according to the season and regional differences). It is best to use a cloudy morning, and the direction of the light is best to be in the light. In terms of queue position, when there are more people, they can be arranged in a square array (for example, 50 - 100 people can be arranged in 4 - 5 rows). The height of the front and back rows should be reasonably arranged by chairs, stools, steps, etc. to avoid blocking. It is recommended to use a small aperture such as F11 or F16 (different cameras may have different aperture ranges). Read more exciting novels for free
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>
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 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>
Is the focal length of the laser focusing lens big or small?
The focal length of a laser focusing lens could not be determined simply. Many factors needed to be considered. From the scanning range and spot diameter, as the focal length increases, the scanning range and spot diameter will increase correspondingly, but the power density will decrease rapidly, which may be unfavorable for processing. Moreover, in the F-Theta field mirror, as the focal length increased, the difference between the actual theta and tg theta would cause the distortion to increase. In terms of laser cutting, different materials and cutting requirements have different requirements for the focal point position (related to focal length). For example, for a small laser cutting machine, the distance between the focusing lens and the material (basically 50.8MM and 63.5MM, etc.), when cutting carbon steel and stainless steel, according to the thickness of the plate, the focus position (related to the focal length) needs to be adjusted to achieve better cutting quality. When the focus of the fiber laser cutting machine is in the best position, the slit is the smallest and the efficiency is the highest to obtain the best cutting result. In the laser marking machine, the focal length of the focusing lens would also affect the effect after focusing. Under ideal circumstances, the position of the focusing point depended on the focal length and the angle of the lens, and the scanning range of the focusing lens was affected by the focal length. Over-increasing the scanning range may cause problems such as the spot becoming thicker and distorting. Therefore, it is necessary to judge whether the focal length of the laser focusing lens is large or small according to the specific application scenarios (such as cutting, marking, etc.), the processing materials, the requirements for power density and the effect of the spot. <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>
Method for converting lens glass radius and focal length
Based on context alone For a thin lens, there is a certain relationship between the focal length (f) of the lens and the radius of curvature (R) of the lens surface. This relationship can be expressed by the lens maker's formula: For a bicive-concave or bicive-concave lens,<<</>>(<</><<</><<</><</>>>/>></>>>,<<</>>/>If it is a plano-concave lens or a plano-concave lens, one of the curvatures has an infinite radius. If the refraction index of the lens is known, as well as the curvature radius of the lens, the focal length of the lens can be calculated by the above formula. However, it should be noted that this formula was based on the thin lens. In practical applications, for thick lenses, a more complicated optical model was needed to accurately describe the relationship between focal length and radius of curvature. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
How to adjust the focal length of an old-fashioned camera lens
For old-fashioned cameras equipped with a zoom lens, the focal length could be changed by turning the zoom ring to achieve the optical zooming effect. The lens was usually marked with a focal length value, and the position of the focal length scale could be used to determine which focal length was used. If a fixed-focus lens was installed on the camera, the focal length adjustment could only be achieved by changing the lens with a different focal length. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
What kind of focal length lens do street models use?
Different focal lengths had different effects and uses when shooting models on the street. The 35mm and 50mm focal lengths were suitable for full-body shots, which could better interpret the background. The 50mm focal length was close to the human eye's vision and had the characteristic of " what you see is what you get ". The 85mm focal length was called the " Portrait Mirror Emperor ". The blurring effect outside the focal length was soft and beautiful, which was suitable for shooting half-body close-ups. The 105mm and 135mm focal lengths were also good choices for street portraits because of their longer focal lengths, but the long focal length would make the photographer and model far away, making communication inconvenient. The 70 - 200mm medium telephoto lens was the most commonly used lens for street shooting. Under the same aperture, the longer the focal length, the better the blurring effect. In addition, the focal length of a portrait was usually set between 50mm and 85mm because the 85mm lens basically did not distort the face and the image compression was strong. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
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. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
On the application of focal length
In the field of photography, focal length was widely used. When shooting portraits, different focal lengths would produce different effects. For example, a focal length of 85mm was a better choice for close-up portraits, which could show a more natural facial features ratio. When shooting close-up portraits with a focal length of 17mm (a wide-angle focal length), the parts close to the lens such as the mouth, nose, and arms would be magnified, easily deformed, and the ratio of the character to the background would be exaggerated. As the focal length increased, the ratio of the character to the background would become more natural, the distance between the five facial features would be shortened, and the face would become flatter. The hairstyle would look thicker, and the face would not be so sharp. For the lens label, if the focal length label on the lens had two numbers (such as 17 - 40mm), it meant that it was a zoom lens, covering the focal length from 17mm to 40mm; if there was only one number (such as 50mm), it was a fixed-focus lens. The smaller the number, the shorter the focal length, the wider the angle of view, and the wider the viewing range. The picture could accommodate more elements but the proportion of each element was small. The larger the number, the longer the focal length, the narrower the angle of view, and the narrower the viewing range. The picture could accommodate fewer elements but the proportion of each element was larger. In some simple self-made microscopes (such as the glue stick microscope with an adjusted focal length), the focal length needed to be adjusted to observe the object (such as garlic film). <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>