Telecentric lens depth of field calculation method

Depth of field is a very important parameter in the camera, and its size determines the clear image range. In telecentric optical imaging, depth of field is also a parameter often mentioned, and its size depends on the lens magnification, aperture number, wavelength, pixel size, and sensitivity of the edge extraction algorithm used by the customer. For most telecentric lenses, the stated depth of field is the overall depth of field at an aperture number of 8. Depth of field can be used for measurement applications. It is usually larger than the depth of field for defect detection. The contrast of the image must be as high as possible.

A simple rule, the quick way to calculate the depth of field is as follows:

Depth of field = (number of working apertures * pixel size * application specific parameters) / (magnification * M magnification)

           M = magnification

          WFN = working aperture

          P = pixel size (microns)

          K = application-specific parameters

    Application-specific parameters depend on the type of application. For a telecentric measurement application, a reasonable application-specific parameter value is 0.015, while the defect detection application-specific parameter should be set to approximately 0.008. For a certain magnification and working aperture, the depth of field of our lens is better because of the double-focus telecentricity

Below we take the calculation of the depth of field of the bi-telecentric lens 2364 as an example to illustrate the calculation formula of the depth of field of the telecentric lens:

The following is the catalog data of bi-telecentric lens 2364:

          M = Magnification = 0.38

           P = pixel size = 4.4um (depending on your camera)

           K = 0.015 (application-specific parameters)

          F / N = number of apertures = 8

           WFN = Number of working apertures == (1 + magnification) * Focal ratio = (1+ 0.138) * 8 = 9.104

Depth of field = (number of working apertures * pixel size * application specific parameters) / (magnification * magnification) = (9.104 * 4, 4 * 0, 015) / (0.138 * 0.138) = 31.55 mm

However, the depth of field data in the bi-telecentric lens catalog is 35mm.

To measure the depth of field of a lens:

         1) Adjust the working distance between your lens and the measured object to the correct position;

         2) Once your picture is in focus, use software to measure your object;

         3) Now move the object closer to the lens and away from the lens, and see the result of your software measurement;

         4) You can see that your imaging image will not change within the allowable range. This range is what we call the depth of field range.