Several technical indicators of the lens
The lens is an extremely important component in visual inspection.Let's take a look at its technical specifications below.
1.Focal length
Focal length is the distance from the main plane of the image to the focal point of the image,such as 16mm or 25mm.The size of the focal length determines the size of the field of view angle.The smaller the focal length value,the larger the field of view angle,and the larger the observed range.Due to the one-to-one correspondence between focal length and field of view angle,a determined focal length means a determined field of view angle.Therefore,when selecting a lens focal length,it is important to fully consider whether the observation details are important or the observation range is important.
2.Aperture index
The aperture index is expressed as F and measured by the ratio of the lens focal length F to the aperture diameter D.Each lens is labeled with a maximum F value,for example,6MM/f1.4 represents a focal length of 6mm,and the aperture index F is 1.4,which can calculate a maximum aperture of 4.29 millimeters.
The luminous flux of the lens is inversely proportional to the square of the F-value,with the smaller the F-value,the greater the luminous flux.The scale values of the aperture index sequence on the lens are 1.4,2.8,4,5.6,8,11,16,22,etc.The pattern is that the exposure amount at the previous scale value is exactly twice the exposure amount corresponding to the latter scale value.That is to say,the aperture of the lens is 1/1.4,1/2,1/2.8,1/4,1/5.6,1/8,1/11,1/16,1/22,respectively.The previous value is√2 times the latter value.Therefore,the smaller the aperture index,the larger the aperture,and the greater the illumination on the imaging target surface.
3.Zoom lens
There are two types of zoom lenses:manual and electric.Manual zoom lenses require manual adjustment of the lens magnification.The automatic zoom lens is a control system that automatically controls the movement of the lens group inside the lens and adjusts the magnification of the lens.
4.Auto focus
The automatic focusing function is to use the computer to analyze the image itself to determine the distance between the lens and the measured workpiece.The visual inspection system achieves focus by moving the Z-axis up and down and adjusting the height of the lens from the workpiece.If the workpiece is not focused,adjacent pixels on the image will have very similar intensities.Adjust the lens height to obtain the image again,determine whether the intensity difference between adjacent pixels increases or decreases,and then determine the direction of Z-axis movement until the maximum value of intensity difference between adjacent pixels is found.The automatic focus function works by utilizing the contrast strength of the image,so there need to be some details that can form contrast in the captured image.
