The closer the target object of the ordinary industrial lens is to the lens (the shorter the working distance), the larger the image formed. When using an ordinary lens for size measurement, there will be the following problems:

　　1. Because the measured object is not in the same measurement plane, the magnification is different;

　　2, lens distortion is large;

　　3, parallax, that is, when the object distance increases, the magnification of the object is also Change;

　　4. The resolution of the lens is not high;

　　5. It is caused by the geometric characteristics of the visual light source The uncertainty of the edge position of the image.

　　Telecentric lens imaging

　　Telecentric lens can effectively solve the above problems of ordinary lenses, and there is no such nature Interpretation error, so it can be used in high-precision measurement, metrology, etc. Telecentric lens is a high-end machine vision lens, usually with superior image quality, especially suitable for size measurement applications.

　　 No matter where, at a specific working distance, the magnification will be the same after refocusing, because the maximum field of view of the telecentric lens is directly related to the lens diaphragm The proximity is related, the larger the lens size, the larger the field of view required. The telecentric measurement lens can provide superior image quality, and the distortion is smaller than that of the traditional fixed lens design focal lens. This optical design makes the image surface more symmetrical and can be used with software for precise measurement.

　　The advantages of ordinary lenses: low cost; practical; wide range of uses.

　　 Disadvantages: the magnification will change; there is parallax.

　　 Application: imaging of large objects.

　　The advantages of a telecentric lens: the magnification is constant and does not change with the depth of field; there is no parallax.

　　 Disadvantages: high cost; large size; heavy weight.

　　 Application: Metrology; CCD-based measurement; Microcrystalline.

　　 The single-lens reflex viewfinder basically means professional positioning, which must also determine the professional path of digital SLR cameras, even if it is for ordinary users and enthusiasts. Has a lot of excitement. Focal length and aperture are the two most important parameters of digital SLR (also known as SLR digital camera or DSLR lens for short.

　　1) wide-angle lens. A wide-angle lens in the traditional sense refers to a lens with a focal length below 35mm, such as a 28mm, 24mm or even 16mm lens. Generally speaking, lenses below 24mm are called ultra-wide-angle lenses. However, because most digital SLRs on the market are not full-frame digital SLRs, the focal length of the lens must be multiplied by 1.5 or 1.6. Therefore, for this type of SLR, 16mm can be considered as an ultra-wide-angle lens.

　　2) Standard lens. Generally speaking, the focal length is 50mm or 85mm. The angle of view of the 50mm lens is closest to that of the human eye, so it is called the 'header'. But it can only be because of this, it is difficult to use a good header, because it is not like an ultra-wide-angle or macro lens, which can take pictures that the human eye cannot perceive. The 85mm lens is generally a portrait lens.

　　3) Medium telephoto lens, generally 100mm or 135mm. The 100mm lens is generally a macro lens, and the 135mm lens is also a portrait lens, but focuses on half-length portraits, while 85mm focuses more on full-body portraits.

　　The focal length of 200mm or more is what we call a telephoto lens. In fact, the lens at this focal length is very useful. It can shoot landscapes, portraits, or ecological photography (such as shooting birds, etc., especially lenses of 300mm or even 400mm or more). However, this type of lens is usually large and heavy, and lacks the help of anti-shake, and there are still many restrictions on its use, so in fact, there are not many opportunities to use it.

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