How to choose industrial lenses for machine vision?

          In the development process of machine vision systems, the selection of industrial lenses is a relatively complex process that requires understanding the specific purpose and application environment of the lens, and then conducting various experimental operations to recognize the parameters after all. Don't buy lenses without acknowledging your practical application, as it may not fully utilize the imaging function of the lens, affect the quality of product testing without clear drawings, and even lead to project development failures and increased costs. Below is an introduction to the selection method of industrial lenses.

1、 Homework distance, focal length

          The homework distance and focal length are often considered in combination. Generally, this approach can be adopted: first, clarify the resolution of the system, combine it with the CCD pixel scale to determine the expansion magnification, and then combine it with spatial structure constraints to determine the approximate object image distance, further estimating the focal length of industrial camera lenses. So the focal length of industrial camera lenses is related to the operating distance, system resolution (and CCD pixel scale) of industrial camera lenses. However, there are still many factors to consider when choosing the focal length, as follows:

          1) Fixed focal length: The focal length remains fixed and can be divided into two types: with aperture and without aperture. Aperture: The size of the lens aperture can be adjusted. According to changes in ambient lighting, the aperture size should be adjusted accordingly. No aperture: refers to a fixed aperture, with a constant amount of light passing through it. Mainly used for stable light sources or industrial cameras with built-in electronic shutters.

           2) Zoom: The focal length can be adjusted according to the needs to expand or reduce the image of the subject. The commonly used zoom lenses are six times and ten times zoom. Three variable lenses: 

adjustable focal length, adjustable focus, and adjustable aperture. Two variable lenses: adjustable focal length, adjustable focus, and automatic aperture. Under the premise of certain lens

 specifications and focal length, the field of view of CS interface lenses will be greater than that of C-interface lenses.       

2、 Image size and image quality

           The image plane size of the selected industrial camera lens should be compatible with the size of the camera's photosensitive surface, following the principle of compatibility 

between larger and smaller - the camera's photosensitive surface cannot exceed the image plane scale indicated by the lens - otherwise, the image quality of the edge field of view 

will not be guaranteed. The requirements for image quality prioritize MTF and distortion. In measurement use, special attention should be paid to distortion.

3、 Lens aperture

          The lens is divided into manual aperture lens and automatic aperture lens according to the aperture. The selection is mainly based on whether the ambient light is stable. For

 stable environments, manual aperture lens is generally selected and can be adjusted once it is OK. Otherwise, automatic aperture lens is selected (it is necessary to equip it with an 

industrial camera with an automatic aperture lens socket), which can achieve automatic scheduling of image brightness. The control signals for automatic aperture lenses can be 

divided into two types: DC and Video control, namely DC voltage control and video signal control. When selecting the type of automatic aperture lens, the connection method for the 

socket of the industrial camera automatic aperture lens, and the driving method switch for selecting the automatic aperture lens, the three can be carefully coordinated and coordinated.

4、 Camera specifications

           The lens specifications are generally divided into 1/3 ", 1/2", 2/3 ", and so on. Under certain circumstances, the relationship between lens focal length and lens field of view is: the longer the lens focal length, the smaller the lens field of view; The relationship between lens specifications and lens field of view is that the larger the lens specification, the larger the lens field of view. Under the condition of a fixed lens object distance, as the focal length of the lens increases, the image size becomes smaller, but the details of the image become clearer; As the camera specifications increase, the image size also increases, but the details of the image become increasingly blurry.