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2023
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Machine Vision Optical Lens Selection
There are several variables that identify lenses, and you need to make decisions about all of these for your vision system. Two of the most fundamental of these variables are focal length and maximum aperture. The focal length will determine the magnification of the image projected onto the image plane, while the aperture will determine the amount of light passing through the sensor. The focal length will also determine the angle of view, with shorter focal lengths allowing a wider field of view and longer focal lengths allowing a narrower field of view. Ultimately, the relationship between the focal length of the lens and the size of the sensor will determine the angle of view of the vision system. With respect to a definite lens, the larger the sensor size of the camera, the wider the field of view. With respect to a definite sensor size, there will be normal, wide-angle, and telephoto (e.g., telephoto) lenses. Once you know your sensor size and desired angle of view, you will be able to use that information to calculate the focal length of your ideal lens. The aperture of the lens - a wider aperture has a smaller f-number than a narrower aperture - is also related to the camera's shutter speed. The faster the shutter speed, the shorter the exposure time and therefore the lower the f-number needed to capture a good image (the wider the aperture).
Before you know which lens to choose, you need to answer a few questions. Whatever your industry, whether automotive, industrial, packaging or food and beverage consumption, you need to apply the following questions to your program application:
What is the field of view (FoV) in millimeters (mm)?
What is your working distance (WD) in millimeters (mm)?
What is the sensor size of your camera in millimeters (mm)?
What is your desired wavelength in nanometers (nm)?
What is the pixel size of your sensor, in microns (μm)?
These are the initial points you need to understand in order to calculate the type of lens you need. The success or failure of your project will likely depend on the accuracy of these key elements, so be prepared - you will reap the rewards when your lenses provide you with crisp, high-resolution images.
Most lenses offer optimal pixel size and wavelength bandwidth. Typically, lenses operate in the visible spectrum, unless specified for near infrared (NIR) or short-wave infrared (SWIR). Most importantly, the resolution of your lens is meaningful with respect to the level of detail required for your application. It is also important to utilize a sensor with the proper resolution and pixel size to resolve the detail required for your application.
The three most common types of lens thread interfaces are C-interface, S-interface, and CS-interface.
C-interface lenses: The most common type of lens mount in machine vision. With an inner diameter of 25.4 mm, a pitch of 0.794 mm and a flange focal length of 17.526 mm, they benefit from the most common accessory options and compatibility.
CS-Mount: A less common lens mount type, but still frequently utilized in machine vision. The main difference here is that the flange focal length is shorter, so you may need an adapter if you are using a camera with a C-mount lens. The measurements are as follows: inner diameter 25.4mm, pitch 0.794mm, flange focal length 12.5mm.
S-Mount: This is a rare type of lens mount for very small lens configurations, often utilized with compact cameras for small size vision systems such as board level cameras. These are completely incompatible with C and CS mounts.
Keywords: intelligent lighting
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