The relationship between the image distance of the camera and the double focal length
When the object distance was greater than 2x focal length, the image distance was between 1x focal length and 2x focal length; when the object distance was equal to 2x focal length, the image distance was also 2x focal length. Read more exciting novels for free
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>
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>
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>
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>
I want to know the relationship between shooting distance and focal length
There was a certain relationship between the shooting distance and the focal length. First of all, the shorter the focal length, the larger the shooting range, and the smaller the subject in the picture. For example, in a surveillance lens, a 12mm lens is more suitable to see people at 10m. Different lenses have corresponding field of view. According to the field of view, the distance between the camera and the object or the width of the object to be seen, the installation distance or the viewing range can be calculated. From the perspective of the viewing range, the focal length of the lens determined the viewing range of the camera, and the focal length was inverse to the angle of view (short focal length, large angle of view; long focal length, small angle of view), and the shooting distance was one of the elements that determined the scene. In photography, these factors influenced each other. For example, a short focal length could capture a larger range of objects even if the shooting distance was relatively close, while a long focal length could capture a larger image ratio when the shooting distance was far. In addition, the focal length and depth of field were also inverse (short focal length, large depth of field; long focal length, small depth of field), and the shooting distance would indirectly affect the depth of field effect. Under different shooting distances, in order to achieve the ideal depth of field effect, it might be necessary to adjust the focal length. In terms of perspective, the perspective of the image was only related to the shooting distance, not the focal length. <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 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>