Telecentric lens technical parameters

1) High image resolution

The image resolution is generally measured by the CTF (Contrast Transfer Function) which quantifies the existing spatial frequency contrast of the image sensor. The unit is lp / mm (coupling number per millimeter). Most machine vision integrators often only gather a large number of cheap low-pixel, low-resolution lenses, and can only produce blurred images in the end. With AFT telecentric lenses, even with small pixel image sensors (such as 5.5 megapixels, 2/3 "), high-resolution images can be generated.

2) Nearly zero distortion

The distortion coefficient is the percentage difference between the physical size and the image sensor image size. Ordinary machine lenses usually have distortions greater than 1-2%, which may seriously affect the accuracy level when measuring. In contrast, the telecentric lens of AFT Optoelectronics passed strict processing and quality inspection, and this error was strictly controlled below 0.1%.

3) No perspective error

When making precise linear measurements in metrology applications, it is often necessary to observe from the standard front of the object (excluding the sides at all). In addition, many mechanical parts cannot be accurately placed, and the measurement time interval is constantly changing. Software engineers need images that accurately reflect the real thing. A telecentric lens can perfectly solve the above confusion: because the entrance pupil can be located at infinity, only the principal rays parallel to the optical axis will be received during imaging.

4) Telecentric design and ultra-wide depth of field

The AFT bi-telecentric lens produced by Shenzhen Dehong Technology Co., Ltd. not only can use the aperture and magnification to enhance the natural depth of field, but also has unparalleled optical effects of non-telecentric lenses: the image does not change when moving objects within a certain object distance range , That is, the magnification is unchanged.

how to choose

In recent years, machine vision has developed rapidly in China. Everyone has a certain understanding of the selection of ordinary lenses in system integration. However, the selection of telecentric lenses is often confused. The lens, in the process of using it, I still do not know what problems to pay attention to. In view of this problem, the matching selection principle of telecentric lenses and cameras is the same as that of ordinary industrial lenses, as long as the size of the target surface is greater than or equal to the target surface of the camera. Please pay attention during use. The area below the objective lens of the telecentric lens is all telecentric imaging, and the area beyond this range is not strictly telecentric imaging. This must be used in actual use. Be careful, otherwise unnecessary deviations will occur.

When choosing a telecentric lens, customers should first understand when to choose a telecentric lens. According to the principle and unique advantages of the telecentric lens, it is best to use a telecentric lens when the inspection object encounters the following 6 conditions:

1) When it is necessary to detect objects with thickness (thickness> 1/10 FOV diameter);

2) When you need to detect objects that are not on the same plane;

3) When it is not clear what the distance from the object to the lens is;

4) When it is necessary to detect a three-dimensional object with an aperture;

5) When low distortion is required and the brightness of the image effect is almost identical;

6) When defects can only be detected under parallel illumination in the same direction.

When choosing a telecentric lens, you should first understand the corresponding conditions of the telecentric lens related indicators:

1) Object-side size ------ shooting range.

2) Image side size ------ the target surface size of the CCD used.

3) Working distance ------ the distance between the front surface of the object lens and the subject.

4) Resolution --------- CCD pixel size used.

5) Depth of field ------------ The range in which the lens can make a clear image. The larger the image / object ratio, the smaller the depth of field.

6) Interface ------------ Camera interface, mostly C, T and other interfaces.

According to the use situation (object size and required resolution), select the object-side lens and CCD or CMOS camera with the appropriate object-side size, and obtain the image-side size at the same time. . The selection process should also pay attention to the effect of the depth of field index, because the larger the image / object ratio, the smaller the depth of field. In order to obtain a suitable depth of field, you may need to re-select the lens.