Industrial lenses come in a wide variety of types and vary greatly in quality. However, general users often do not pay enough attention to industrial lenses when designing machine vision systems, which can lead to unsatisfactory images or even system development failures.
The function of an industrial lens is optical imaging. Industrial lenses are crucial components of machine vision systems, playing a key role in image quality. They influence several key image quality indicators, including resolution, contrast, depth of field, and various aberrations.
I. Classification of Industrial Lenses:
1. Classification based on the size of the effective image field:
Camera lenses can be categorized into television camera lenses, film camera lenses, and still camera lenses. Television camera lenses are further divided into 1/4 inch, 1/3 inch, 1/2 inch, 2/3 inch, and 1 inch lenses, among others.
2. Classification by focal length:
Based on whether the focal length is adjustable, industrial lenses can be divided into two main categories: fixed focal length lenses and zoom lenses. Fixed focal length lenses can be further divided into four categories: fisheye lenses, short focal length lenses, standard lenses, and telephoto lenses. Zoom lenses can be divided into manual zoom and power zoom lenses.
3. Classification based on industrial lens interface type:
There are many different types of interfaces between industrial lenses and industrial cameras. Commonly used interfaces for industrial cameras include C-mount, CS-mount, F-mount, V-mount, T2-mount, Leica-mount, M42-mount, and M50-mount. The type of interface is not directly related to the performance or quality of the industrial lens; it simply represents a different interface method. Adapters between various commonly used interfaces can usually be found.
C-mount and CS-mount are the most common international standard interfaces for industrial cameras. They are 1-inch-32UN imperial threaded connectors. The thread connection of C-type and CS-type interfaces is the same. The difference lies in the back focal length: C-type interface has a back focal length of 17.5mm, while CS-type interface has a back focal length of 12.5mm. Therefore, industrial cameras with CS-type interfaces can be used with both C-type and CS-type lenses, but a 5mm adapter ring is required when using C-type lenses; industrial cameras with C-type interfaces cannot use CS-type lenses.
F-mount lenses are the interface standard for Nikon lenses, hence the name Nikon mount. They are also a commonly used type in industrial cameras. Generally, industrial cameras with a sensor size larger than 1 inch require F-mount lenses.
V-mount lenses are the standard primarily used by the renowned professional lens brand Schneider, and are also generally used in industrial cameras with larger sensor surfaces or for special purposes.
Other special-purpose lenses:
Microscope lenses are generally used in imaging systems with an imaging ratio greater than 10:1. However, since the pixel size of modern industrial cameras has been reduced to within 3 micrometers, microscope lenses are also used when the imaging ratio is greater than 2:1.
A macro lens generally refers to a specially designed lens with an imaging ratio ranging from 2:1 to 1:4. When image quality requirements are not very high, a magnified image effect can usually be achieved by adding a close-up adapter ring between the lens and the industrial camera, or by adding a close-up lens in front of the lens.
Telecentric lenses are lenses specially designed to correct parallax in traditional lenses. Within a certain object distance range, the magnification of the image does not change with the object distance. This is very important for applications where the objects being measured are not on the same object plane.
Ultraviolet (UV) lenses and infrared (IR) lenses are generally designed for use within the visible light range. Because the same optical system has different refractive indices for different wavelengths of light, light of different wavelengths emitted from the same point cannot converge into a single image, resulting in chromatic aberration. Common lenses are designed to achromatic out of the visible light range; UV and IR lenses are specifically designed for ultraviolet and infrared light, respectively.
II. Selection of Industrial Lenses:
Lenses are categorized by aperture into manual aperture lenses and automatic aperture lenses. The choice primarily depends on the stability of the ambient light. Manual aperture lenses are generally used in stable environments, and once the initial setup is successful, they are sufficient. Conversely, automatic aperture lenses are used in less stable environments (requiring an industrial camera with an automatic aperture lens mount), enabling automatic brightness adjustment. The control signals for automatic aperture lenses can be divided into DC and VIDEO control, i.e., DC voltage control and video signal control. Proper coordination is crucial in selecting the type of automatic aperture lens, the connection method of the industrial camera's automatic aperture lens mount, and the selection of the automatic aperture lens drive switch.
With a fixed lens specification (lens specifications are generally divided into 1/3″, 1/2″, and 2/3″, etc.), the relationship between lens focal length and field of view is as follows: the longer the focal length, the smaller the field of view; with a fixed focal length, the relationship between lens specification and field of view is as follows: the larger the lens specification, the larger the field of view. With a fixed object distance, as the focal length increases, the image area decreases, but the image details become clearer; conversely, as the lens specification increases, the image area increases, but the image details become increasingly blurred.
Fixed focal length: The focal length is fixed and can be divided into two types: with aperture and without aperture. With aperture: The aperture size of the lens can be adjusted. The aperture size should be adjusted according to changes in ambient light. Without aperture: Also known as fixed aperture, its light transmission is constant. Mainly used in situations with constant light sources or industrial cameras with built-in electronic shutters. Zoom lens: The focal length can be adjusted as needed to magnify or reduce the image of the subject. Commonly used zoom lenses are 6x and 10x zoom. Triple variable lens: Adjustable focal length, focus, and aperture. Diple variable lens: Adjustable focal length, focus, and automatic aperture. Given a fixed lens specification and focal length, the field of view of a CS-mount lens will be larger than that of a C-mount lens.
When the focal length can be fixed, a fixed-focus lens is used. This lens has only one manually adjustable focus ring (marked with several distance reference values). Rotating this ring left and right will make the image on the CCD target surface as clear as possible, resulting in the clearest image on the monitor screen. Manual zoom lenses are generally used in situations where requirements are more stringent and fixed-focus lenses are difficult to meet. Zoom lenses should generally be consistent with the specifications of the industrial camera, or the lens specifications should be larger than the camera specifications. All camera lenses are threaded. There are two industrial standards for CCD camera lens mounting: C-mount and CS-mount. Both have the same thread, but the distance from the lens to the photosensitive surface differs. C-mount: The distance from the lens mounting reference surface to the focal point is 17.526mm. CS-mount: The distance from the lens mounting reference surface to the focal point is 12.5mm. To mount a C-mount lens to a CS-mount camera, the gasket at the front of the camera should be removed before installing the lens. Otherwise, a lens converter is required.
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