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Focus: In physics, it refers to the convergence point of parallel light rays after being refracted by a lens or reflected by a curved mirror. In photography, when an infinitely distant parallel light enters the camera lens, the point where the light is refracted to the lens 'main axis is the focal point of the lens. This is also the clearest point of the scene captured by the lens. It can be composed of the main focal point and many secondary focal points. Focus Plane: It is the general term for the first focal plane and the second focal plane. The plane that passes through the first focal point (front focal point or object focal point) and is vertical to the main optical axis of the system is called the first focal plane (also known as the front focal plane or object focal plane), and the plane that passes through the second focal point (back focal point or image focal point) and is vertical to the main optical axis of the system is called the second focal plane (also known as the back focal plane or image focal plane). According to the principle of lens imaging, there was always a clear position on the film or sensor of a camera. The plane formed by countless such clear points was the focal plane, and the place where the sensor was installed in the camera was at the focal plane. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>

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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>

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>

The focus of the camera was also called the photography assistant or the big assistant in the production team. In addition to cooperating with the photographer to ensure the completion of the filming mission, they also had to arrange the division of labor between the specific members of the photography team and communicate with other departments on various details. Focus was the prerequisite for a good photo. The reasons for the photo being out of focus might be that the basic skills were not up to standard, it was too late to focus in an instant, the quality of the phone or camera was not up to standard, it was over-cropped, and it was compressed during transmission. In a movie, the difficulty of focusing was not directly related to the number of special effects. For example, although Champion had few special effects, the reaction time for the focal point crew was reduced by half due to the shooting speed of 48 frames per second ("upgraded" shooting). Moreover, a large number of action scenes used "sports shots + telephoto shooting + upgraded speed," so the difficulty of focusing was very high. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>