Industrial lens classification by field of view

With the industrial lens as the apex, the angle formed by the object image of the measured object passing through the two edges of the maximum range of the lens is called the field of view angle. In other words, the field of view is the size of the object that can be seen when the lens is connected to the CCD camera. The size of the field of view determines the field of view of the optical instrument. The larger the field of view, the larger the field of view and the smaller the optical magnification.

According to the size of the camera's field of view: small field of view lens, standard lens, wide-angle lens and extra wide-angle lens, telecentric lens, microscope head, microscope head and other types.

Standard lens

A lens with an angle of view of about 50 degrees and a focal length close to the diagonal length of the camera frame is also the angle that a person's single eye can see without turning their heads and eyes, so it is also called a standard lens. The focal length of a standard lens of a 5mm camera is mostly 40mm, 50mm, or 55mm, and the focal length of a standard lens of a 120mm camera is mostly 80mm or 75mm. The larger the CCD chip, the longer the focal length of the standard lens.

Wide-angle and ultra-wide-angle lenses

The angle of view is above 90 degrees, which is suitable for shooting scenes with a large distance and a large range, and can deliberately exaggerate the foreground to show a strong sense of distance, that is, perspective. A typical wide-angle lens for a 35mm camera has a focal length of 28mm and a viewing angle of 72 degrees. A 50 and 40mm lens for a 120 camera is equivalent to a 35 and 28mm lens for a 35mm camera.

Long focal length lens

Suitable for shooting distant scenes. A small depth of field can easily make a subject with a blurred background stand out, but it is bulky and difficult to focus on a dynamic subject. 35mm camera long focal length lenses are usually divided into three levels, below 135mm is called the middle focal length, 135-500mm is called the long focal length, and above 500mm is called the super long focal length. The 150mm lens of the 120 camera is equivalent to the 105mm lens of the 35mm camera. Because the long focal length lens is too bulky, there is a telescopic lens design, that is, a negative lens is added behind the lens, and the main plane of the lens is moved forward, and the short focal length can be obtained with a shorter lens body.

Reflective telescope head

It is another kind of super telescope lens design, which uses a mirror surface to form the image, but because of the design, it is not possible to install an aperture, and only the shutter can be used to adjust the exposure.

(2) Wide-angle and ultra-wide-angle lenses: The angle of view is above 55 °. The wide-angle and ultra-wide-angle lenses have shorter focal lengths and larger angles of view than standard lenses. For a 135 camera, a focal length of about 30mm and a viewing angle of about 70 ° are called wide-angle lenses; a focal length of about 22mm and a viewing angle of about 90 ° are called ultra-wide-angle lenses. "

(3) Telephoto and ultra-telephoto lenses: Within a 20 ° angle of view, telephoto and ultra-telephoto lenses have a longer focal length and a smaller angle of view than standard lenses. For a 135 camera, a focal length of about 20mm and a viewing angle of about 12 ° is called a telephoto lens; a focal length of more than 300mm and a viewing angle of less than 8 ° is called a super telephoto lens.

(4) Fisheye lens and reflective lens: Fisheye lens seems to be an extreme ultra-wide-angle lens. It uses the distortion of the lens to obtain a great angle of view. The angle of view is about 180 °, because its huge angle of view is similar to the angle of fisheye. name. Reflective lenses, also known as fold-reflective lenses, are actually a super-telephoto lens. They are short and fat, about half as short as telephoto lenses of the same focal length, and light in weight. Convenience.

(5) Zoom lens: The focal length has a certain range of variation. Its lens focal length can be freely adjusted within a larger range, and it plays the role of several fixed-focus lenses with different focal lengths. It also has two types of manual zoom and electric zoom, which can capture the image of the field of view of the monitored scene and the target with a zoom distance, which is suitable for long-distance change observation and capture of the target. The characteristics of a zoom lens are: in the case of clear imaging, the image size and field of view are changed by changing the focal length of the lens.

(6) Macro lens, perspective adjustment lens and leather cavity lens: Macro lens, also called colossus lens, is a kind of lens that can produce colossus effect. Perspective adjustment lens, also known as shift lens, is a special lens used to adjust the perspective effect or depth of field effect of an image. A leather cavity lens is a lens that uses a hose-type leather cavity to connect to a 135 camera.

Pinhole lens: The lens tip is only a few millimeters in diameter and can be concealed for installation. Pinhole lenses or prism lenses are suitable for use in environments with cover or special requirements.At this time, standard lenses are easily damaged or easily found.Using pinhole lenses or prism lenses can meet similar special requirements, such as in industrial kiln. Furnaces and mental hospitals.

Micro lens

If you have strict requirements on the working distance, you can consider using a macro lens. A general wide-angle lens and an appropriate extension tube can achieve the macro effect. In addition to macro photography at extremely close range, telephoto can also be taken.

Telecentric lens

Telecentric lenses generally have a smaller field of view. From the perspective of the machine vision industry, most telecentric lenses are between 0.5 and 2 times. There are also more than 2 times telecentric mirrors, such as 4X, 8X and so on.

Microscope head

Generally, when the field of view is very small, such as below 1mm, because our sensors are usually a few mm (more between 4.8 ~ 8.8), so if you need to take a field of view of about 1mm and below, the general CCTV is not able to Meet this requirement. Therefore, you can consider using a microscope head, which can be magnified several times or ten times.

Determine the desired field of view (FOV) and working distance (WD), and then calculate the focal length (f) of the industrial lens based on these two requirements and the known target surface size. The calculation formula is:

Focal length f = WD × target size (H or V) / FOV (H or V)

Field of View FOV (H or V) = WD × target size (H or V) / focal length f

Field of View FOV (H or V) = target surface size (H or V) / optical magnification

Working distance WD = f (focal distance) × target surface size / FOV (H or V)

Optical magnification = target surface size (H or V) / FOV (H or V)