The focal point and the focal plane of the camera
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. Read more exciting novels for free
the focal length of a camera lens
The focal length was the division of the focal length of the lens. It was generally divided into super wide angle, wide angle, standard, medium focal length, medium telephoto, telephoto, and super telephoto. Take a 35mm camera (135 camera) as an example: a lens with a focal length below 20mm is an ultra-wide-angle lens; a lens with a focal length of 21mm-40mm is a wide-angle lens; a lens with a focal length of 41mm-60mm is a standard lens; a lens with a focal length of 61mm-100mm is a medium-focal lens; a lens with a focal length of 101mm-180mm is a medium-long focal lens; a lens with a focal length of 180mm-300mm is a telephoto lens; A lens with a focal length of 301mm or above was a super telephoto lens. Different focal lengths had different characteristics and applicable scenes. For example, the ultra-wide angle lens had a wide angle of view, which was suitable for shooting large scenes such as scenery and architecture; the standard lens was close to the human eye's angle of view, with very little distortion, which was more suitable for documentary photography; the telephoto lens could achieve background blurring, compress space, and highlight the main body, but the scene was small, so it was difficult to blend the background with the main body well. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
Phone camera focal length
The focal length of a cell phone camera could be categorized into many categories and uses: - ** Ultra-wide-angle lens **: A lens with a focal length between 6mm and 16mm is called a "fisheye lens". It is an extreme ultra-wide-angle lens. The angle of view is more than 180 degrees, and some can reach 230 degrees. It is more entertaining. The "ultra-wide-angle camera" in the smartphone had a focal length of about 16mm, which was usually 0.6 times the focal length of the main camera. The ultra-wide-angle camera mode in the camera APP was also known as "0.6X zoom." It was suitable for shooting tall buildings and scenery. After optimization, it could be used as a "super macro lens." - ** Wide-angle lens **: A lens with a focal length between 24mm and 35mm is a "wide-angle lens". It has a smaller focal length and a wider angle of view. It can record a wide space and is called a "master lens". The focal length of the main camera in the field of smart phones was usually 25mm-28mm, also known as the "wide-angle main camera." The 1X focal length (main focal length) had good image quality, suitable for shooting portraits, buildings, scenery, documentary and many other scenes. - ** Portrait lens (standard lens)**: A lens with a focal length between 35mm and 70mm is considered a "standard lens". Among them, the 50mm focal length has the best effect. When shooting portraits, the distortion is small and the background blurring effect is good. It can highlight the main body of the character. In the field of smart phones, the 50mm focal length is about twice that of the wide-angle main lens. It can be called a portrait lens or an equivalent 2X telephoto lens. - ** Telephoto lens **: Generally speaking, a focal length of 70mm or above is a "telephoto lens", but the standard for smart phones is lower. A focal length greater than 50mm is considered a telephoto lens. The focal length of the telephoto lens of a traditional mobile phone could reach up to about 90mm (equivalent to a 3X telephoto lens). Different phone models had different focal lengths. Single-camera phone lenses were mostly wide-angle lenses with an equivalent focal length of about 22mm-30mm; multi-camera phones often used wide-angle lenses as the main camera, combined with ultra-wide-angle or telephoto lenses. For example, the 0.5x focal length was equivalent to the 13mm focal length of the single-lens reflex, which was suitable for shooting large scenes; the 1x focal length was equivalent to the 26mm focal length of the single-lens reflex, which was suitable for portraits and cultural documentary shooting. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
camera focal length factor
For digital cameras, because the area of their CCDs or sensors was smaller than that of traditional 135 cameras (35mm full-frame), when using the same lens, the imaging area was smaller than that of a film camera, resulting in fewer scenes falling on the imaging element than traditional 135 cameras. This gave rise to the concept of focal length coefficient. The focal length coefficient was calculated as the ratio of the length of the film to the length of the corresponding side of the CCD. For example, if the film is calculated as 24mm, the corresponding side length of the CCD-side is 12mm, and the coefficient is 2. When using lenses on different frame cameras, the focal length needed to be converted by a factor. For example, the Canon APS-C camera needed to be multiplied by a factor of 1.6. For example, a 100mm fixed-focus head hung on the APS-C body would have an equivalent focal length of 160mm, while the Canon APS-C classic head's actual focal length of 18 - 135mm would be 28 - 216mm. The focal length coefficient made it so that when the lens was used on different frame cameras, although the angle of view had an equivalent change, the depth of field and perspective effect were still the same as the original lens. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
The focal length of the surveillance camera
In an optical system, the focal length of the surveillance camera was the distance from the optical center point of the lens to the camera's CCD-based/CMOS-based sensor. It can also be understood as the distance from the center of the lens to the focal point of the light when parallel light is incident. The size of the focal length determined the image size, field of view, and depth of field of the surveillance image. Generally speaking, the larger the focal length, the farther the view, and the smaller the field of view. The smaller the focal length, the closer the view, and the larger the field of view. The focal length of mainstream surveillance cameras was generally 2.8mm, 3.6mm/4mm, 6mm, 8mm, 12mm, 16mm, etc. Some even had a zooming function. Cameras with different focal lengths are suitable for different monitoring ranges. For example, for situations where 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 3.6mm or 4mm focal length camera can have a viewing angle of 75°-90 °, an effective monitoring distance of more than 5 meters, and can cover 40 - 80 degrees of space); for a larger monitoring range (such as a space of 10m * 10m), you need to choose a surveillance camera with a larger focal length. <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>
Photographer focal point
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>
What's the focal length of the camera?
There were many values to choose from for the focal length of the camera. The common ones were 2.8mm, 3.6mm, 4mm, 6mm, 8mm, 16mm, 32mm, and so on. Cameras with different focal lengths had different monitoring ranges, angles, and distance characteristics. Generally speaking, the smaller the focal length, the larger the monitoring angle, the closer it would be. For example, the 2.8MM lens could reach 100 degrees, but the distance was about 5 meters. The larger the focal length, the farther the monitoring angle would be. For example, the 12mm lens could reach 26 degrees, and the distance could reach about 35 meters. In addition, when selecting the focal length, it can also be determined by the calculation formula f = h×D × H (where f is the focal length, h is the horizontal size of the sensor, D is the object distance, and H is the object width) according to the parameters such as the object distance, object width, and the sensor width. It can also be selected by estimation according to the use scene. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
The focal length of a direct-focus camera
In direct-focus photography, when the eyepieces of the telescope were removed, leaving only the main mirror, the lens of the DSLR was also removed to expose the LCD sensor, and then the telescope was directly connected to the DSLR (may require an M42 ring). At this time, the focal length of the telescope's main mirror was the focal length of the lens. For example, when using the MK20240 for direct-focus photography, the focal length was 2400mm, so the focal length of the lens was 2400mm. <a href="/?from=ask_words" style="color:red" target="_blank">Read more exciting novels for free</a>
The difference in the focal length of the surveillance camera
For surveillance cameras, there were many differences in focal length: 1. ** Image size **: The focal length affects the image size of the captured image. 2. ** Field of view **: - The larger the focal length, the smaller the field of view. With the lens as the apex, the angle formed by the two edges of the largest range of the object image through the lens would be smaller. The range of the viewing angle would be smaller, but the relative details would be clearer. - The smaller the focal length, the larger the field of view, and the larger the range of view, but the lower the degree of recognition. 3. ** Depth-of-field **: Depth-of-field refers to the distance between the front and back of the object being photographed when the camera lens can obtain a clear image. The depth of field was different at different focal lengths. 4. ** Surveillance Distance **: - The larger the focal length, the farther the surveillance camera could shoot. It was suitable for monitoring distant targets or large areas, such as outdoor rectangular areas. - The smaller the focal length, the closer the surveillance shooting distance. It was suitable for monitoring closer targets or areas with a small range and a large viewing angle, such as indoor square areas such as family living rooms and small shops. <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>